by Jack Norris, RD, LD
- Introduction to the Omega-3 Fatty Acids
- Essential Fatty Acids: ALA and LA
- Long-chain Omega-3 Fatty Acid Blood Levels of Vegetarians
- Conversion of ALA to EPA and DHA
- ALA Supplementation Results in Little Increase in Blood DHA
- EPA and DHA Correlate between Plasma and the Heart but not the Brain
- Tissues Contain Enzymes that Convert Omega-3s
- Dietary DHA Reduces ALA Conversion
- Lower Omega-6 Intake is Associated with Higher Serum EPA and DHA
- DHA Supplementation in Vegetarians
- Omega-3 Recommendations for Vegans
- Vegetarian Pregnancy and Children
- Omega-3s and Chronic Disease
Introduction to the Omega-3 Fatty Acids
There are two questions regarding vegetarians and omega-3s: Do vegetarians have negative health consequences from not eating fish and should vegetarians supplement with omega-3s?
For our purposes, there are three important omega-3 fatty acids:
- alpha-linolenic acid (ALA) – short-chain (18 carbon) omega-3 fatty acid. Found in small amounts in animal flesh, in very small amounts in a variety of plant products, and in relatively large amounts in soy, walnuts, canola oil, flaxseeds and their oil, hempseed oil, camelina oil, and chia seeds. The human body cannot make its own ALA; it must be obtained through the diet.
- eicosapentaenoic acid (EPA) – long-chain (20 carbon) omega-3 fatty acid. Found mostly in fatty fish, in small amounts in eggs, and in very small amounts in seaweed that can be concentrated into supplements. Some EPA is converted into series 3 eicosanoids which can reduce blood clotting, inflammation, blood pressure, and cholesterol. The human body can produce EPA from ALA and possibly from DHA.
- docosahexaenoic acid (DHA) – long-chain (22 carbon) omega-3 fatty acid. Found mostly in fatty fish, in small amounts in eggs, and in very small amounts in seaweed that can be concentrated into supplements. DHA is a major component of the gray matter of the brain, and also found in the heart, retina, testis, sperm, and cell membranes. The body can convert EPA into DHA.
A chart showing the conversion pathways for the omega-3 fatty acids can be found in The Fatty Acids.
See the video below for an excellent overview of omega-3 fatty acids from omega-3 researcher Dr. Richard Bazinet of the University of Toronto (2021).
Essential Fatty Acids: ALA and LA
The Institute of Medicine considers there to be a dietary requirement for two fatty acids for people age 1 year and older:
- alpha-linolenic acid (ALA) – the short-chain omega-3 (described above) which can be low in some vegan diets.
- linoleic acid (LA) – the short-chain (18-carbon) omega-6, which is prevalent in most vegan diets due to being abundant in vegetable oils.
Because they’re essential fatty acids, there’s a daily dietary reference intake (DRI) for both ALA and LA:
- ALA: 1.6 g (males age 14+), 1.1 g (females age 14+)
- LA: 17 g (men age 19-50), 12 g (women age 19-50)
Essential Fatty Acid Intakes of Vegans
The table below shows the weighted averages of studies measuring vegan ALA intakes. Calculations and citations are in our ALA Intakes spreadsheet.
The World Health Organization and Food and Agriculture Organization (2010) recommend an LA intake between 2.5-9% of calories, saying that the lower number prevents deficiency and the higher end of the range reduces the risk for heart disease.
Although vegans who don’t ensure sources of ALA tend to have a high ratio of omega-6 to omega-3 fats, their percentage of calories as LA has been shown to be 5.1% (Pinto, 2017, United Kingdom), 7.3% (Allès, 2017, France), 8.5% (Kornsteiner, 2008, Austria), and 9.3% (Rizzo, 2013, USA), well within the range recommended by the WHO. Because of this, we’re hesitant to recommend that vegans avoid LA.
Long-chain Omega-3 Fatty Acid Blood Levels of Vegetarians
Summary: The differences in long-chain omega-3 blood levels between vegans, lacto-ovo-vegetarians, and omnivores aren’t obviously physiologically significant, especially with regard to omnivores who don’t regularly eat fish. Red blood cell DHA of vegetarians and vegans is roughly 72-75% of that of omnivores, but it’s not clear if this has clinical significance.
There is no standardized method for measuring omega-3 fatty acids: no one knows what levels of fatty acids in any given medium represent a deficient, healthy, or optimal level. It could even be that blood levels of fatty acids have little bearing on omega-3 fatty acid status. The purpose of this section is to determine whether vegans do indeed have lower blood levels of long-chain omega-3 fatty acids than omnivores. Early studies found that vegans have lower EPA and DHA blood levels, but these studies were conducted on very few people; more recent studies haven’t shown nearly the difference.
As of early 2022, we’ve tracked 27 studies measuring the blood levels of omega-3 fatty acids in vegetarians. We list these studies and their measurements in the Cross-sectional tab of our spreadsheet, Omega-3s Part 2: Research.
The way omega-3s are measured among these studies varies considerably.
Fatty acids can be measured in various components of plasma such as phospholipids, triglycerides, or cholesterol esters. Fatty acids may also be measured in the adipose tissue, platelets, or red blood cells. Because red blood cells have a lifespan of 120 days, red blood cell fatty acids might be a more accurate long-term representation of omega-3 status.
In the plasma, omega-3s are usually measured as a percentage of total fatty acids, but Welch et al. (2010) measured omega-3s as a concentration in plasma and Rosell et al. (2005) provided the data to calculate a concentration. Concentrations might be a more accurate reflection of the body’s omega-3 stores since they represent an absolute rather than a relative amount.
DPA is a long-chain omega-3 fatty acid that is an intermediary between EPA and DHA. We emphasize studies that included DPA in their measurements because DPA represents a significant fraction of long-chain omega-3s that vegans have converted from ALA and which can potentially be converted to DHA.
The graph below plots all measurements that compared total long-chain omega-3 levels (EPA+DPA+DHA) of vegetarians or vegans to omnivores. It includes measurements of percentages and concentrations for each medium. While there’s considerable overlap between diet groups, individual studies generally find that omnivores have higher levels of long-chain omega-3s than vegans with the differences being statistically significant.
The graphs below compare only the EPA or DHA levels of vegans and vegetarians in all studies that measured EPA or DHA.
Arguably the most important metric is red blood cell omega-3s, shown in the graph below.
It’s hard to conclude much regarding vegan long-chain omega-3 levels from these studies given that the measurements aren’t standardized, aren’t well understood, and contain significant overlap. Arguably a more accurate way to assess this data is to weight the comparisons of vegetarians both proportional to the omnivores in the same studies and proportional to how many people were in each diet group while limiting the measurements to one per population studied.
In order to get the most accurate picture of how long-chain omega-3 blood levels of vegans compare to those of omnivores, we decided to calibrate the measurements by creating a ratio of the levels of vegans to those of omnivores rather than using an absolute amount. We did this by simply dividing the vegan level by the omnivore level.
For example, the study by Kornsteiner et al. found an EPA+DPA+DHA percentage of total fatty acids in red blood cells of 1.96% for vegans and 3.34% for omnivores. The study by Li et al. found an EPA+DPA+DHA percentage of total fatty acids in plasma of 3.6% for vegans and 5.5% for omnivores. We don’t know if we can compare the percentage of fatty acids in red blood cells to the fatty acids in plasma, but we can compare the ratio of vegan to omnivore long-chain omega-3s in both studies, which was .59 in Kornsteiner et al. and .65 in Li et al. We can then multiply these two ratios by the number of vegans in their respective study, divide by the total number of vegans in both studies, and get a weighted average of the ratio of vegan to omnivore long-chain omega-3s across both studies. By weighting all of the studies in this way, we can obtain the most accurate picture of how blood levels of long-chain omega-3 fatty acids compare for vegans and omnivores.
Most studies measured omega-3s as a percentage of total fatty acids; to be as consistent as possible, we weighted the percentage of total fatty acids rather than the concentration for studies that measured both. For studies with multiple measurements, we chose in this order: red blood cells, plasma, platelets, and adipose tissue.
The table below shows the weighted proportions of omega-3s for vegetarians and vegans compared to omnivores for all studies and for red blood cell (RBC) measurements only. Calculations and citations are in the Cross-sectional tab of our spreadsheet, Omega-3s Part 2: Research.
Based on the table above, vegans generally have lower blood levels of long-chain omega-3s than omnivores. Since plasma levels of omega-3s are at least in part a representation of dietary fatty acids, as distinct from representing only the body’s ability to convert dietary short-chain to long-chain omega-3s, it’s not surprising that people who have an intake of long-chain omega-3s have higher blood levels.
Vegetarians vs. Fish-Eaters
Among people who don’t supplement with long-chain omega-3s, regular fish-eaters will be the only dietary group with a significant source of long-chain omega-3s. According to the USDA nutrient database, a medium egg contains about 2 mg of EPA and 16 mg of DHA. That provides lacto-ovo-vegetarians with very small amounts of dietary EPA and DHA.
There are two studies that measured omega-3 levels among fish-eaters (Welch, 2010; Miles, 2019), but neither measured it in red blood cells. We analyze these studies in the Fish-eaters tab of our spreadsheet Omega-3s Part 2: Research and summarize the results in the three charts below. Participants in the studies didn’t use long-chain omega-3 supplements.
Welch et al. (2010) measured omega-3 plasma concentrations and separated omnivores into groups who did and did not eat fish. There were only 10 vegans.
We combined the male and female long-chain omega-3 plasma concentrations to determine how vegans compared to both fish-eating and non-fish-eating omnivores. Because there were so few vegans, we also combined the lacto-ovo-vegetarians (LOV) with the vegans for a “vegetarian” category. The table below shows that lacto-ovo-vegetarians, vegans, or the combined group had levels slightly below fish-eaters and either similar or higher levels than non-fish-eaters.
Miles et al. (2019) compared the percentage of omega-3 fatty acids in the adipose tissue of pescatarians to other dietary groups, as shown in the table below. Vegetarians and vegans had lower levels than omnivores and even somewhat lower levels than fish-eaters. Although vegans had substantially lower levels than fish-eaters in this study, it’s not clear what the percentages of fatty acids in adipose tissue represent; possibly nothing of clinical significance.
Fatty Acid Levels of Older vs. Younger Vegans
It’s normally thought that people have a harder time converting ALA to EPA and DHA as they age. Sarter et al. (2015) found that 69 vegans aged 60 to 85 had EPA+DHA levels of about 4.0% compared to about 3.6% for 97 vegans aged 20 to 59 (p for trend = 0.009).
Impacts of Lower EPA and DHA on Vegetarians
A possible benefit of long-chain omega-3 fatty acids, especially EPA, is to reduce blood clotting which protects against heart attacks. There have been some differences noted in blood clotting between vegetarians and omnivores.
Mezzano et al. (1999, Chile), found that vegetarians had significantly more platelets (242,000 per ul) than non-vegetarians (211,000 per ul) and a shorter bleeding time (4.5 vs. 7.3 min). In a follow-up study, Mezzano et al. (2000, Chile) gave vegetarians 700 mg EPA and 700 mg DHA for 8 weeks. EPA went from .2 to 1.8% and DHA went from 1.1 to 3.0%. Some clotting factors changed, but bleeding time remained lower at 5-1/2 minutes.
Sanders and Roshani (1992, United Kingdom) found that only one of eight platelet aggregation parameters in vegan men, but not women, was different from the non-vegetarians. Bleeding times were similar.
Pinto et al. (2017, United Kingdom) compared heart rate variability between a group of 23 adult vegans and 24 omnivores. Low heart rate variability reflects a reduced capacity for the heart to respond to the body’s physiological demands and is linked to an increased risk for heart disease. As expected, the vegans had lower concentrations of DHA and EPA in both red blood cells and plasma. While vegans had a higher heart rate variability over a 24-hour period, their daytime heart rate variability was lower, and their heart rate was greater. The clinical significance of these findings aren’t clear.
Thus, of three studies that looked at clotting factors, the results are mixed.
In terms of cognition, in their study of British mortality, Appleby et al. (2002) found vegetarians to have a barely statistically significant, higher risk of death from mental and neurological diseases (DRR 2.21, CI 1.02–4.78). In contrast, a more recent report from EPIC-Oxford (Appleby, 2016) found that vegetarian deaths from mental and behavioral disorders were not statistically different from non-vegetarians (HR 1.22, CI 0.78–1.91). And a report from the Adventist Health Study-2 (Orlich, 2013, USA) found no difference in mortality from neurologic diseases between vegetarians and non-vegetarians (HR 0.93, CI 0.67-1.29); pescatarians and semi-vegetarians were included in their vegetarian category so the results can’t be extrapolated to vegetarians who don’t eat fish.
Conversion of ALA to EPA and DHA
Measurements of the percentage of total fatty acids as EPA and DHA in the blood are generally considered a marker of omega-3 status. This assumes that higher percentages of total fatty acids in the blood reflect higher and more optimal amounts in the tissues that utilize omega-3s. It also assumes that when blood percentages change due to changes in dietary intake, levels in tissues respond similarly.
In this section, we examine these assumptions. Evidence of omega-3 conversion enzymes in tissues and down-regulation of omega-3 conversion in response to dietary omega-3s suggest that the body can regulate the conversion of omega-3 fatty acids in tissues independent of the percentage in the blood.
There’s evidence that high intakes of EPA and DHA will increase their percentages in both blood and tissues, but it’s not clear if higher percentages are necessary for optimal health. We assess the evidence in our sections Impacts of Lower EPA and DHA on Vegetarians and Omega-3s and Chronic Disease.
ALA Supplementation Results in Little Increase in Blood DHA
Our ALA Trials spreadsheet lists a handful of clinical trials, including all of the trials with vegetarians of which we’re aware, investigating whether increasing dietary ALA subsequently increases the percentage of long-chain omega-3s in the blood. The changes in total fatty acids as long-chain omega-3s show a wide variation with no clear pattern; some even found a decrease in DHA. On average, EPA+DPA+DHA increased by 43.5% while DHA only increased by 4.6%.
It’s safe to say that supplementing with ALA is unlikely to substantially increase the blood percentage of fatty acids as DHA in most adults.
EPA and DHA Correlate between Plasma and the Heart but not the Brain
Summary: Based on limited, mostly cross-sectional data, there appears to be a robust correlation between the blood and tissue percentages of EPA+DHA in the human heart but not the brain or sperm.
Studies of ALA supplementation result in very little increase of DHA in the blood, but how much evidence is there to suggest that this reflects the body’s inability to convert ALA to DHA for tissue utilization?
A basic question is, without any dietary changes, how much do blood levels of omega-3 fatty acids typically correlate with tissue levels? It’s difficult to study the omega-3 content of tissues in living humans. In our spreadsheet, Tissue Correlations, we list the correlations between blood and tissue percentages of omega-3s in both humans and animals. A summary of the results follows.
Harris et al. (2004) measured the correlation between the percentage of EPA+DHA in red blood cells and the percentage of EPA+DHA in the hearts of 20 heart transplantation patients having routine heart biopsies, 13 of whom were considered to be high consumers of EPA and DHA; they found a statistically significant, strong correlation (R = 0.82, P ≤ 0.0001).
Harris et al. (2004) also performed an intervention: Heart transplantation patients (n=25) with low EPA+DHA intakes were provided 1,000 mg of EPA+DHA for 6 months. These patients had weaker correlations between red blood cell and heart EPA+DHA at baseline (R = 0.47, P = 0.031). Post-intervention measurements showed that EPA+DHA percentages increased in plasma, red blood cells, heart, and cheek tissue; the correlation between red blood cell and heart EPA+DHA remained the same (R = 0.47, P = 0.06).
Metcalf et al. (2007) placed a series of patients on ALA (5.8 g per day) or EPA+DHA (6.3 g, ~50% each) for a number of weeks based on their heart surgery schedule. While they didn’t test for a correlation between red blood cell and heart omega-3 fatty acid percentages, the percentages between the two mediums were fairly similar and differed from the control group in similar amounts post-treatment (see our spreadsheet ALA Trials).
Cunnane et al. (2012) performed autopsies on cognitively normal people and found a correlation between percentages of DHA in plasma phosphatidylethanolamine and the angular gyrus region of the brain DHA (R = 0.77, P ≤ 0.005). However, they failed to find correlations between DHA and other regions or in cognitively impaired people stating, “No significant correlations were observed for DHA (% or mg/g) or any other fatty acids in the other brain regions or in the [Alzheimer’s disease] and [mildly cognitively impaired] groups (data not shown).”
Carver et al. (2001) performed autopsies on 58 people and found a negative correlation between the DHA percentage in red blood cells and the cerebral cortex of people aged >18 years; it’s likely this correlation doesn’t achieve statistical significance after a Bonferroni correction for the large number of correlations tested.
Chamorro et al. (2020) measured the fatty acid percentages of young men, comparing vegans (n=34) and omnivores (n=33). They didn’t test for a correlation between the percentage of omega-3s in plasma or red blood cells and sperm. The ratio of the percentage of EPA in sperm to that in plasma and red blood cells was similar at 0.54 for each, but the ratios for DPA and DHA were not. See the table below.
There’s much more data from animals than humans. Our spreadsheet, Tissue Correlations, lists 24 correlations between blood and tissue percentages of EPA+DHA among rats, pigs, and mice. The strength of the correlations varies considerably with some being negative.
There’s one other study on animals worth mentioning. Talahalli et al. (2010) fed two groups of rats a reasonable amount of ALA (2.5% and 5.0% of calories). After 60 days, the percentage of fatty acids as DHA in the brain of the rats fed 2.5% and 5.0% ALA was, respectively, 9.4% and 10.4% compared to 8.3% in the control group (see the table, Talahalli 2010). This suggests that ALA supplementation increased the amount of DHA in their brains.
One significant caveat for comparing the conversion of omega-3s in rats, pigs, and mice to humans is that rats, pigs, and mice normally don’t have a dietary source of EPA or DHA and, therefore, would normally rely entirely on the conversion from ALA for any EPA or DHA.
Tissues Contain Enzymes that Convert Omega-3s
Two critical enzymes, delta-5 desaturase and delta-6 desaturase, convert short-chain omega-3 and omega-6 fatty acids into long-chain versions.
Previously, the liver was considered the primary site of EPA and DHA production for peripheral tissue utilization, but studies by Cho et al. (1999a and 1999b) found substantial amounts of mRNA for the delta-5 and delta-6 desaturase enzymes in many tissues of human cadavers.
Cho et al. (1999a) found that delta-5 desaturase mRNA was greatest in the human liver, but that the heart, brain, and lung also contained substantial amounts. They found low but detectable levels in the placenta, skeletal muscle, kidney, and pancreas. Cho et al. (1999b) found that the amount of delta-6 desaturase mRNA in the human liver was comparable to that found in the human lung and heart, while the adult brain had a level several times greater than the liver.
Cho et al. (1999a) point out that the expression of these enzymes can vary greatly among individuals. The authors hypothesize that this might be due to age or, more likely in their view, regulation of the enzymes in response to the dietary intake of fatty acids.
Using cross-sectional data based on the percentage of plasma phospholipids, Welch et al. (2008, United Kingdom) estimated that non-fish-eaters (both vegetarians and meat-eaters) convert ALA to long-chain omega-3s at about a 22% higher rate than fish-eaters.
Dietary DHA Reduces ALA Conversion
In a series of three studies, researchers used a carbon tracer to track the conversion of a 700 mg dose of ALA to long-chain omega-3s in the blood of three different groups of people. The results are in the table below. Only females (all of whom were of reproductive age) showed a substantial conversion of ALA to DHA in the blood.
In addition to the baseline measurements listed in the table above, Burdge et al. (2003) included an 8-week intervention on three groups of older men: a control group (n=5), a group whose daily ALA was increased from their normal intake of 1.7 g to 10 g (n=4), and a group whose daily EPA+DHA was increased from their normal intake of 264 mg to 1.6 g (n=5). After 8 weeks, they fed each person 700 mg of ALA with a carbon tracer and found that the ALA supplemented group’s conversion of ALA to long-chain omega-3s hadn’t increased whereas the EPA+DHA supplemented group’s conversion had decreased.
Vermunt et al. (2000) fed carbon-labeled ALA to humans and found that the conversion of ALA to EPA, DPA, and DHA was much greater after 9 weeks of a diet high in oleic acid compared to after a diet high in ALA or EPA+DHA.
The two trials mentioned above by Burdge et al. (2003) and Vermunt et al. (2000) suggest that there’s a down-regulation of ALA conversion to long-chain omega-3s in humans who have a regular supply of ALA or EPA and DHA. The simplest explanation for this down-regulation is that their tissues had sufficient long-chain omega-3 levels.
Further evidence for enzymatic regulation due to dietary intake is a study by Metherel et al. (2019) who conducted a randomized controlled trial using carbon-labeled DHA. While plasma levels of EPA increased, it wasn’t due to DHA being converted to EPA, suggesting that the dietary supply of DHA resulted in the down-regulation of the conversion of EPA to DHA.
Burdge and Wootton’s data (2002) showed an uneven distribution of omega-3 fatty acids among the different components of plasma lipids (cholesterol esters, phosphatidylcholine, triglycerides, and non-esterified fatty acids). They surmised that plasma cholesterol esters act as a long-term source of ALA within circulation that may provide tissues containing active desaturation and elongation pathways (brain, heart, and skeletal muscles) a steady source of ALA for conversion to EPA, DPA, and DHA while tissues with low expressions of these enzymes, such as the kidney and pancreas, may be dependent upon the supply of pre-formed EPA, DPA, and DHA.
Lower Omega-6 Intake is Associated with Higher Serum EPA and DHA
The traditional way vegetarians have been encouraged to raise blood EPA and DHA levels is by increasing ALA and decreasing the omega-6 fatty acid, linoleic acid (LA). This is because the enzymes that convert ALA into EPA and DHA also convert the omega-6 fatty acids and there is competition for these enzymes. Some evidence for this theory is from a clinical trial by Liou et al. (2007, Canada) who found increasing LA intake resulted in a lower percentage of EPA in plasma phospholipids
Most vegetable oils are high in omega-6s and vegetarians tend to get plenty in their diets. Sanders and Younger (1981, United Kingdom) found a dietary ratio of omega-6s to omega-3s of 16 for vegans and 6 for meat-eaters. Sanders and Roshanai (1992, United Kingdom) found a dietary ratio of 15.8 for vegan men, 10.2 for meat-eating men, 18.3 for vegan women, and 8.2 for meat-eating women.
There are no clinical trials that increase the ALA intake of vegetarians while also decreasing their LA intake, to see what impact this has on blood levels of EPA and DHA.
Salvador et al. (2019, Spain) studied 55 vegans and 49 lacto-ovo-vegetarians and found that those with a serum omega-6 to omega-3 ratio of ≤ 10 had a higher percentage of serum EPA and DHA than those with a ratio between 10 and 20 or >20 (EPA: 0.60%, 0.27%, and 0.23%; DHA: 2.90%, 1.91%, and 1.19% respectively). Flaxseed intakes of once per day and, especially, 2 or more times per day were associated with a much higher percentage of serum ALA (~0.5% vs. ~0.7% and 1.5%, respectively), but not with higher EPA or DHA percentages.
Based on limited research, lowering LA intake could increase blood levels of long-chain omega-3s, but it’s not known if doing so impacts tissues or provides health benefits.
Low Omega-6 to Omega-3 Ratio Foods
At this time, the research indicates that vegetarians with lower dietary omega-6 to omega-3 ratios tend to have higher blood levels of EPA and DHA. For that reason, it’s prudent, when adding ALA to the diet, to choose foods that don’t also substantially increase omega-6 intake, listed in the table below.
|Foods with Lowest Omega-6 to Omega-3 Ratios|
|flaxseeds||1:4||1.6 g / tablespoon|
|flaxseed oil||1:4||2.5 g / teaspoon|
|chia seeds||1:3||5 g / oz|
|canola oil||2:1||1.3 g / tablespoon|
|English walnutsa||4:1 – 5:1||2.6 g / oz (14 halves)|
|walnut oil||5:1||1.4 g / tablespoon|
|soybean oil||7.5:1||.9 g / tablespoon|
|black walnuts||10:1||.9 g / oz|
|aEnglish are the typical walnuts found in most grocery stores.|
DHA Supplementation in Vegetarians
Studies consistently show that supplementing vegetarians and vegans with DHA from algal sources increases their blood percentage of DHA (Sanders, 2009; Geppert, 2006; Wu, 2006; Conquer, 1996; Conquer, 1997). Studies also show that supplementing with both EPA and DHA increases vegetarians EPA and DHA percentages (Sarter, 2015; Mezzano, 2000).
Fish contains about twice as much DHA as EPA (Kris-Etherton, 2009), so it’s not unusual for fish-eaters to eat more DHA than EPA. Conquer and Holub (1996, Canada) showed an 11–12% increase in EPA after 6 weeks of 1,620 mg of DHA in vegetarians.
Upon DHA supplementation, EPA levels also increase by a small percentage. Using a carbon tracer, Brossard et al. (1996, France) found a 1.4% conversion of DHA to EPA in three people given one dose of 123 mg of DHA over the course of 20 hours. In contrast, Metherel et al. (2019, Canada) conducted a randomized controlled trial using DHA containing labeled carbon and didn’t find any to be converted to EPA. They conclude that “the increase in plasma EPA following DHA supplementation in humans does not occur via retroconversion, but instead from a slowed metabolism and/or accumulation of plasma EPA.”
Omega-3 Recommendations for Vegans
To sum up the rationale behind our recommendations, it appears that if a vegan is meeting the Dietary Reference Intake for ALA, their EPA status should be adequate. To be cautious we recommend either increasing ALA intake or adding a DHA supplement. Please see our article, Daily Needs, for specific recommendations and how to meet them.
There are many vegan DHA and EPA supplements available via the Internet. We aren’t able to assess whether any given company is better than another.
Vegetarian Pregnancy and Children
DHA may be important for developing fetuses and infants, and pregnant women more efficiently convert ALA to DHA. Fetuses and infants are able to receive DHA that’s released from the mother’s fat tissues and provided through the umbilical cord or breast milk.
Anthropologist John H. Langdon argues that DHA is not an essential nutrient for the brain development of infants because in cases of very low maternal levels of DHA, infants can utilize other fatty acids for brain tissue which can later be replaced by DHA (Langdon, 2006).
Reddy and Sanders (1994, United Kingdom) measured the DHA levels in umbilical cords of 32 infants born to vegetarian mothers compared to omnivores and found no relationship between the proportions of DHA in plasma or cord artery phospholipids and the birth weight or head circumference of the infants.
Many children have been raised vegan without supplementing with DHA, or even extra ALA, and appear to develop well. Even so, it’s prudent for breastfeeding mothers of vegetarian or vegan children to ensure they’re meeting omega-3 recommendations (see Daily Recommendations) and non-breastfeeding infants should receive infant formula with 500 mg of EPA+DHA per day.
Omega-3s and Chronic Disease
Most of the concern with regard to low plasma levels of EPA and DHA among vegetarians is due to studies that have found an association between low EPA and DHA blood levels and an increased risk of chronic diseases such as cardiovascular, cognitive decline, and depression. These associations have generally been consistent but weak. There have also been some associations between omega-3 blood levels and an increase in some chronic diseases. In this section we review the evidence.
Omega-3s and Cardiovascular Disease
Research on omega-3s and cardiovascular disease has examined the associations with fish consumption, blood levels of omega-3s, and omega-3 supplementation.
Fish Consumption and Cardiovascular Disease
As of February 2021, the American Heart Association was still basing its omega-3 fatty acid recommendations on its 2002 position paper, Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease (Kris-Etherton, 2002) which recommends that adults “Eat a variety of (preferably oily) fish at least twice a week. Include oils and foods rich in alpha-linolenic acid (flaxseed, canola, and soybean oils; flaxseed and walnuts).”
Some recent reports include:
- A 2020 meta-analysis of six cohort studies found no correlation between eating fish and a reduced risk of cardiovascular disease or mortality (Zhong, 2020).
- A 2020 Cochrane review determined that there wasn’t enough evidence to assess the impact of eating fish on cardiovascular health (Abdelhamid, 2020).
- A 2016 meta-analysis of 12 prospective studies found a reduced risk of mortality with increasing fish intake (Zhao, 2016).
Omega-3 Supplementation and Cardiovascular Disease
In what they called “the most extensive systematic assessment of effects of omega‐3 fats on cardiovascular health to date,” a 2020 Cochrane Review analyzed 86 randomized controlled trials of 12 to 88 months duration using omega-3 capsules, omega-3-enriched food, or dietary advice to eat more omega-3s (Abdelhamid, 2020). The review found little to no effect of increasing omega-3s on all-cause or cardiovascular mortality, cardiovascular events, stroke, or arrhythmias. Increased omega-3 intake showed a trend with reduced coronary heart disease mortality (RR 0.90, CI 0.81-1.00) and there was a reduced rate of coronary heart disease events (RR 0.91, CI 0.85-0.97). Increasing long-chain omega-3s reduced triglycerides by ~15% in a dose‐dependent way. Overall, the authors stated that 334 people would need to increase their long-chain omega-3 intake to prevent one person from having a coronary heart disease event and they believed this wasn’t enough of an impact to recommend supplementation.
In contrast, a 2019 meta-analysis of omega-3 supplementation found a benefit from omega-3 supplementation in the combined results from 13 randomized controlled trials using about 800 to 1,800 mg of omega-3 fatty acids per day (Hu et al.). At baseline, the participants had a mixed risk for cardiovascular disease: 40% had diabetes and 73% were using cholesterol-lowering medication. In one set of results, that excluded the REDUCE-IT trial described below, they found a reduced risk of heart attack (RR 0.92, CI 0.86-0.99) and cardiovascular death (RR 0.93, CI 0.88-0.99). The omega-3 supplementation in this set of results is arguably higher than the AHA recommendations of at least 2 servings of fish per week, but not implausible. For the omega-3 content of fish, see Omega-3 Fatty Acids: Fact Sheet for Health Professionals.
The Reduction of Cardiovascular Events with Icosapent Ethyl-Intervention Trial (REDUCE-IT) was excluded from Hu et al.’s results above because it used a much higher dose of omega-3s: 4,000 mg/day of a purified form of EPA. It showed markedly better success for heart attack (RR 0.69, CI 0.58-0.81) and cardiovascular death (RR 0.80, CI 0.66-0.98). Participants also had a lower risk of stroke (RR .72, CI 0.55-0.93), but their death from all causes wasn’t significantly lower (RR .87, CI 0.74-1.02) than the placebo (Bhatt, 2019). The extremely high amount of EPA used in REDUCE-IT is a pharmacological dose and not relevant to dietary omega-3 intake.
Omega-3s and Cognition
A 2012 cross-sectional report from the Framingham Study examined 1,575 people (54% women) with an average age of 67 (SD 9) years with respect to omega-3 blood levels and numerous cognitive-related parameters (Tan, 2012). They compared the EPA+DHA red blood cell membrane fatty acids in the lowest quartile (≤4.4%) to those in the upper three quartiles (75th percentile was 6.5%). They found that those in the lowest quartile had a significantly lower cerebral brain volume (equivalent to approximately two years of brain aging), but a similar white matter hyperintensity volume, temporal horn volume, and rate of silent stroke. Low blood EPA+DHA was associated with a poorer score on some tests of cognition.
As part of the Women’s Health Initiative Study of Cognitive Aging, Ammann et al. (2013, USA) conducted a cross-sectional analysis of 2,302 women 65 years and older and found no difference in cognition between those in the upper one-third compared to those in the lowest one-third of EPA+DHA percentage of fatty acids in red blood cells. However, the lowest one-third had an average EPA-plus-DHA of 3.8% which is quite a bit higher than vegans tend to have, so this finding doesn’t necessarily reassure us about the omega-3 status of vegans. A 2017 study by Ammann et al. (described below), followed a much larger group of participants over time and provides more insight into whether higher EPA and DHA percentages are important in preventing cognitive impairment and dementia, especially in older women.
Zhang et al. (2016) conducted a meta-analysis of 21 case-control and prospective studies and found that increases of 1-serving/wk increments of fish were associated with a reduced risk of dementia (RR 0.95, CI 0.90-0.99) and Alzheimer’s disease (RR 0.93, CI: 0.90-0.95). DHA intake was also inversely associated with risks of dementia (RR 0.86, CI 0.76-0.96) and Alzheimer’s disease (RR 0.63, CI 0.51-0.76). However, blood levels of omega-3 fatty acids were not associated with a reduced risk of these or other cognitive diseases. In a letter to the editor, Koch and Jensen point out that in the six studies looking at the association between fish intake and dementia and Alzheimer’s disease, one study was a 2-year follow-up of another study with a longer follow-up. Koch and Jensen argue that “Appropriate exclusion of the report from Kalmijn et al. would render the meta-analysis of fish intake in relation to dementia risk insignificant (RR: 0.96; 95% CI: 0.91, 1.01; no heterogeneity) and change the RR estimate for AD risk to 0.87 (95% CI: 0.77, 0.98) in a random-effects meta-analysis with significant between-study heterogeneity still present.” Zhang and Jiao responded that it was appropriate to include both reports. It’s perplexing that omega-3 intakes but not blood levels would be associated with a reduced risk of dementia if there is a true effect, though it might suggest that blood levels of EPA and DHA aren’t an accurate representation of omega-3 status.
Amman et al. (2017, USA) conducted the largest prospective study to assess the risk of dementia with omega-3 fatty acid status. The study was part of the Women’s Health Initiative Memory Study testing the impact of the hormones estrogen and progestin on the memory of women ≥65 years old. Although the hormone part of the study was concluded early, the researchers continued to follow 6,706 women for an average of 9.8 years to see if baseline EPA and DHA levels were associated with a diagnosis of probable dementia (PD) or mild cognitive impairment (MCI). The study compared the risk of PD and MCI among those with EPA/DHA within one standard deviation above the mean (5.3-6.8% EPA+DHA) to those within one standard deviation below the mean (3.8-5.3% EPA+DHA). In one of their models, the researchers found a statistically significant reduction in PD (HR 0.91, CI .83-.99), but most models found no significant association including one that adjusted for the APOE genotype associated with Alzheimer’s Disease (HR 0.92, CI 0.83-1.01). The researchers calculated that the increased risk of PD represented a 2% reduced risk (12% vs. 14%) of PD incidence over a 15-year period. There were no significant associations between EPA+DHA and MCI. Examining EPA and DHA separately produced no significant findings.
In summary, studies of omega-3 fatty acids conducted on populations of omnivores consistently find some significant associations with better cognition, though they tend to be weak. That dietary intakes are more strongly associated with better cognition, than are blood levels, raises a question about whether omega-3s are responsible for the beneficial association rather than other variables paired with omega-3 intake.
Omega-3s and Depression
Our interest in omega-3s and depression is mostly related to whether vegetarians are at an increased risk of depression due to lower EPA or DHA levels.
Risk of Depression
Deane et al. (2019) conducted a meta-analysis and systematic review of 32 randomized controlled trials and found no effect of increasing EPA and DHA on the risk of depressive symptoms (RR 1.01, CI 0.92-1.10). Studies had a median duration of 12 months with a median dose of 0.95 grams per day (ranging from 0.4 to 3.4 grams per day). One study addressed omega-3s and anxiety and found little to no effect. The researchers recommend against taking omega-3 supplements for reducing depression and anxiety risk.
Treatment for Depression
Whether EPA or DHA can be used to treat people with depression is only loosely related to the omega-3 status of vegetarians, but it’s where most of the research has focused and so we review it here.
Early research on treating depressive symptoms with supplementation of EPA and DHA was mixed. In a 2006 review, Sontrop and Campbell found that supplementation improved depression but it wasn’t clear whether it was effective for depressed patients in general or only those with abnormally low concentrations of EPA and DHA. In another 2006 review, Appleton et al. found “little support” based on the small number of trials with significant variation. In a 2007 meta-analysis Lin and Sue found a positive effect of supplementation but with significant publication bias. In a 2009 meta-analysis, Martins found evidence that EPA is more effective than DHA.
Grosso et al. (2014) conducted a meta-analysis of 11 trials of patients with a DSM-defined diagnosis of a major depressive disorder (MDD) and 8 trials of patients with depressive symptomatology but no diagnosis. They found supplementation to have a beneficial effect for the patients diagnosed with MDD and also for those with bipolar disorder. They considered EPA to be more effective, with many trials using pharmacological doses. Hallahan, et al. (2016) found similar results in their meta-analysis.
In their meta-analysis, Luo et al. (2020) found a benefit from high-dose (≥2 g/day) but not low-dose (<2 g/day), EPA/DHA supplementation in the early therapy period for MDD.
Omega-3s and Increased Risk of Disease
Some studies have associated higher ALA intakes with an increased risk of disease.
A 2009 systematic review and meta-analysis (Simon, 2009) of ALA intake and prostate cancer found:
When examined by study type (i.e., retrospective compared with prospective or dietary ALA compared with tissue concentration) or by decade of publication, only the 6 studies examining blood or tissue ALA concentrations revealed a statistically significant association. With the exception of these studies, there was significant heterogeneity and evidence of publication bias. After adjustment for publication bias, there was no association between ALA and prostate cancer (RR: 0.96; 95% CI: 0.79, 1.17).
A 2010 meta-analysis found that subjects who consumed more than 1.5 g/day of ALA had a significantly decreased risk of prostate cancer (0.95, 0.91-0.99) compared to those who ate less (Carayol, 2010).
A 2018 paper from Harvard School of Public Health suggested that past associations between ALA and prostate cancer might have been due to trans-ALA which has been largely removed from the food supply (Wu, 2018).
A 2013 study suggested that DHA supplementation might cause prostate cancer. This concern is probably unwarranted, though if you are at a high risk for prostate cancer you might want to moderate any supplementation. More details can be read in the article, DHA Supplements and Prostate Cancer.
A 2001 analysis from the Nurses Health Study found an almost statistically significant increase in age-related macular degeneration for those with the highest ALA intake (Cho, 2001, USA).
In contrast, a 2013 study found that higher ALA levels in the blood were associated with a lower risk of late age-related macular degeneration (Merle, 2013, France). And a 2017 follow-up from the Nurses Health Study found that a high intake of ALA was associated with an increased risk of intermediate age-related macular degeneration before 2002, but not afterward when less trans fats were found in participants’ blood (Wu, 2017, USA).
A 2005 analysis from the Nurses Health Study found that both the highest intakes of ALA and LA were associated with an increase in lens opacity, which can lead to cataracts (Lu, 2005, USA). For ALA, the risk ratio was 2.2 (1.2, 4.5) for about 1.26 g compared to .86 g per day. A 2007 analysis of the same group found that the highest category of ALA intake (about 1.26 g per day) was linked to a 16% increase in eye lens nuclear density compared to the lowest category (about .84 g per day) over five years. As of 2018, no follow-up studies appear to have been conducted on ALA and cataracts (Lu, 2007, USA).
Without more definitive research we don’t believe concerns about eyesight is any reason to avoid plant-based ALA due to the small differences in ALA intake in these studies, the fact that much ALA in meat-based diets comes from animal products, that trans ALA is no longer added to the food supply, and the large number and inconsistencies of associations between different fatty acids and various conditions.
Last updated May 2022
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