Omega-3s Part 2—Research

Last updated April 2018

More Information on Omega-3s

Introduction to the Omega-3 Fatty Acids

For our purposes, there are three important omega-3 fatty acids:

  • ALA is a short chain (18 carbon) omega-3 fatty acid. It is 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 seed oil. The human body cannot make its own ALA – it must be obtained through the diet.
  • EPA is a long chain (20 carbon) omega-3 fatty acid. It is 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 out of ALA and out of DHA.
  • DHA is a long chain (22 carbon) omega-3 fatty acid. It is found mostly in fatty fish, in small amounts in eggs, and in very small amounts in seaweed that can be concentrated into supplements. It is a major component of the gray matter of the brain, and also found in the retina, testis, sperm, and cell membranes. The body can convert EPA into DHA.

All three of these omega-3 fatty acids may prevent heart arrhythmias, though ALA has been studied the least in clinical trials.

A chart showing the conversion pathways for the omega-3 and omega-6 fatty acids can be found in The Fatty Acids.

Heart Disease

As of May 2012, 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 (31) 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).”

Whether fish or fish oil substantially reduces the risk of cardiovascular disease is somewhat controversial and a topic beyond the scope of this article. The Linus Pauling Institute at Oregon State University provides a good review of the literature in their article, Essential Fatty Acids. Vegetarians already have about a 24% lower risk of heart disease (5), and it is not clear that more EPA or DHA could further benefit them to any significant degree. The main concern is with the possibility of cognitive problems in vegetarians due to long-term DHA deficiency.

Omega-3s and Depression

A 2007 meta-analysis from Taiwan (8) and a 2006 review from Canada (9) found that supplementation with EPA and DHA improved depression, but a 2006 review from the UK (10) found that it did not. There’s some evidence that EPA may be more effective than DHA in treating depression (42).

Omega-3s and Cognition

One cross-sectional study found that higher omega-3 status was associated with some aspects of better cognition. Low omega-3 status was associated with lower brain mass equivalent to approximately two years of brain aging (40).

Another cross-sectional study on women 65 years and older found no difference in cognition between the those in the upper one-third compared to those in the lowest one-third of EPA-plus-DHA percentage of fatty acids in red blood cells (43). However, the lowest one-third had an average EPA plus DHA percentage of 3.8 which is quite a bit higher than average vegan percentages tend to be, so it’s not clear if this finding would apply to vegans who aren’t making an effort to increase their omega-3 intake.

Omega-3 Intakes of Vegetarians

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. Vegans who are not supplementing have an intake of essentially no EPA and DHA.

Three studies have listed the amount of ALA intake for vegetarians (who were presumably not purposefully adding rich sources of ALA to their diets). See Table 3.

Table 3. ALA Intake of Vegetarians
Study Population Intake (g/day)
Australia, 1999 (15) 17 vegetarian men, ~26-42 yrs 1.9
UK, 1984 (25) 10 vegan men 1.8
UK, 1984 (25) 10 vegan women 1.2
UK, 2010 (28) 5 vegan men 1.0
UK, 2010 (28) 5 vegan women .9

It appears that vegetarians meet about 50–60% of the daily ALA recommendations without special diet planning.

Vegans and vegetarians have been shown in many studies to have lower levels of long chain omega-3 fatty acids (EPA and DHA) than meat eaters. Table 4 shows the results of some of these studies. The general trend is that lacto-ovo vegetarians and vegans have lower levels of EPA and DHA in their blood.

Table 4. EPA and DHA Levels in Vegans
Number EPA DHA
1981 UK17 %PCPG %PCPG
Vegans 4 0.3 1.3
Non-Veg 5 1.4 4.1
Vegans 4 0.3 0.9
Non-Veg 5 0.8 2.8
1992 UK16 %PTPG %PTPG
Vegans 20 0.2 0.8
Non-Veg 20 0.9 2.1
1999 Chile18 %PFA %PFA
Vegetarians 26 0.35 1.56
Non-Veg 26 0.79 2.58
2002 Australia33 %PPL %PPL
Vegan 18 1.5 0.9
Lacto-Ovo 43 1.9 1.2
Moderate Meat 60 1.9 1.6
High Meat 18 1.9 1.5
2005 UK19 mg/l mg/l
Vegan 232 .34 .70
Lacto-Ovo 231 .52 1.16
Non-Veg 196 .72 1.69
2010 UK28 µmol/l µmol/l
Men Vegan 5 65 195
Lacto-Ovo 25 56 222
Meat Eaters (no fish) 359 47 215
Fish Eaters 2,257 58 240
Women Vegan 5 50 286
Lacto-Ovo 51 55 224
Meat Eaters (no fish) 309 57 241
Fish Eaters 1,891 65 271
2014 USA39 %RBC %RBC
Vegan 40 .56 2.28
Meat Eaters
(low fish)
78 .40 2.61
2017 UK41 %PFA %PFA
Vegan 23 .47 .91
Meat Eaters 24 1.03 2.23
Vegan 23 .67 2.07
Meat Eaters 24 1.26 4.19
%PCPG—percentage of plasma choline phosphoglycerides • %PG—percentage of plasma phosphoglycerides • %PFA—percentage of plasma fatty acids • %PTPG—percentage of platelet phosphoglycerides • %PPL—percentage of platelet phospholipids • %RBC—percentage of red blood cell fatty acids

One exception is the 2010 UK study in which vegan women had, on average, higher DHA levels than even the fish-eaters. There were only 5 vegan women making the finding unlikely to be statistically significant; the average DHA level was 286 µmol/l with a standard deviation of 211 µmol/l. That means that one or two of the vegan women had very high levels of DHA but some had very low. The researchers didn’t assess how long the vegans had been following their diet.

Lower blood levels of EPA and, especially, DHA in vegetarians doesn’t necessarily mean that they have lower levels of EPA or DHA in other tissues, but it is something to be careful about until more is known.

Effects of Low EPA and DHA on Vegetarians

One of the main things that long chain omega-3 fatty acids do, particularly EPA, is reduce blood clotting which protects against heart attacks. There have been some differences noted in blood clotting between vegetarians and meat-eaters.

A 1999 Chile study (18) 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 2000 Chile study (4), vegetarians were given 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 did change, but bleeding time remained higher at 5 1/2 minutes.

In a 1992 UK study (16), only one of eight platelet aggregation parameters in the men (but not the women) was different from the non-vegetarians. Bleeding times were similar.

Thus, of two studies that looked at these factors, vegetarians were doing worse than meat-eaters in one, but were basically the same in the other.

In terms of depression and cognition, there has been no research on omega-3s and vegetarians, but Joel Fuhrman, MD, has a private practice seeing many long-term vegans and has observed some older vegan men with very low DHA levels and cognitive problems, so there is reason to be prudent regarding DHA in older vegans, especially men (link).

To bolster this theory, here is an excerpt from a paper on DHA and Alzheimer’s Disease:

Docosahexaenoic acid (DHA), a dietary essential omega-3 fatty acid concentrated in membrane phospholipids at synapses and in retinal photoreceptors is decreased in [the Alzheimer disease] brain. This deficiency may be due to enhanced free radical–mediated lipid peroxidation, decreased dietary intake, and/or impaired liver DHA shuttling to the brain. Decreased DHA serum content correlates with cognitive impairment. Moreover, epidemiologic studies suggest neuroprotective consequences of diets enriched in omega-3 fatty acids (37).

A 2017 study from the UK compared heart rate variability between a group of 23 adult vegans and 24 omnivores
(41). Low heart rate variability reflects a reduced capacity for the heart to respond to the body’s physiological demands and is linked to 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. It’s not clear if this is an overall better or worse heart variability for vegans.

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 is 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 (32).

A 1994 study measured the DHA levels in umbilical cords of 32 infants born to vegetarian mothers compared to omnivores (30) 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.

In a study comparing breast milk, cow’s milk formula with DHA, soy formula with DHA, and soy formula without DHA, infants who ate soy formula without DHA had indications of slower parasympathetic development, though still within the normal range (87).

Many children have been raised vegan without supplementing with DHA, or even extra ALA, and appear to develop well (see Real Vegan Children). Despite this, breastfeeding mothers of vegetarian or vegan children should make sure they’re meeting omega-3 recommendations (see Daily Recommendations) and non-breastfeeding infants should receive an infant formula with 500 mg of omega-3 fats per day.

Traditional Remedy: Take more ALA, Reduce LA

The traditional way that vegetarians were encouraged to raise EPA and DHA levels was by increasing ALA and decreasing linoleic acid (LA), a short chain omega-6 fatty acid. The body can convert ALA into EPA and DHA. The enzymes that do this conversion also convert LA into longer chain omega-6s, and can be saturated with omega-6s if there is a lot in the diet. If they are saturated with omega-6s, they are not able to convert omega-3s.

Most vegetable oils are high in omega-6s and vegetarians tend to get plenty in their diets. A 1981 UK study (17) showed that the dietary ratio of omega-6 to omega-3 fats was 16 for vegans and 6 for meat-eaters. A 1992 UK study (16) showed a ratio of 15.8 for vegan men vs. 10.2 for meat-eating men, and 18.3 for vegan women vs. 8.2 for meat-eating women. An ideal ratio is thought be about 3 or 4.

To deal with this problem, in the late 90s and 00s, vegetarian health professionals recommended increasing ALA intake and decreasing LA intake. Unfortunately, there are no long-term studies looking at vegetarians’ blood EPA and DHA after following these recommendations. But we do have some related studies.

A 1999 study (Table 5) of 17 vegetarian men in Australia (15), aged about 26 to 42 years old, showed that four weeks of 3.7 g of ALA per day (the equivalent of about 1.5 teaspoons of flaxseed oil) did not significantly increase the percentages of EPA or DHA in the blood. The same study showed that four weeks of 15.4 g of ALA (the equivalent of about 6.5 teaspoons of flaxseed oil) did increase EPA levels, but still did not increase DHA levels. There was no change in clotting factors (bleeding time was not reported).

Table 5. Effects of ALA Supplementation: 1999 Australian Study
Baseline After 4 wks of 3.7 g ALA per day After 4 wks of 15.4 g ALA per day
ALA 0.1 0.1 0.3
EPA 0.3 0.3 0.5
DHA 1.1 1 0.9^
ALA 0.3 0.4 1.4^
EPA 0.8 0.9 1.4^
DHA 2 2.1 1.9
ALA 1.2 2.5^ 7.4^
EPA 0.2 0.3 .4^
DHA 0.2 0.2 0.2
%PTPL – percentage of platelet phospholipids
%PPL – percentage of plasma phospholipids
%PTG – percentage of plasma triglycerides
^Statistically significant result compared to baseline

A 2000 study from The Netherlands (20) showed no change in EPA or DHA after 4 weeks of 2.0 g of ALA per day in 9 vegans aged 20 to 60 years old. By adding that much ALA, the ratio of dietary LA:ALA went from 13.7 to 6.7.

A 2014 study from the USA (38) put the same group of lacto-ovo vegetarians on three different daily regimens for 8 weeks each: 1 oz of walnuts (3.0 g of ALA), 1 regular egg (110 mg DHA), and 1 fortified egg (~500 mg DHA, 40 mg EPA, 1 g ALA). The ratio of n-6:n-3 was 6:1 in the walnut phase and DHA levels did not increase.

In a 1981 UK study (17), 4 vegans aged 26 to 37 years took 6.5 g of ALA per day for 2 weeks. They had some increase in EPA and DHA levels. See Table 6.

Table 6. Effects of ALA Supplementation: 1981 UK Study
Baseline 2 weeks of 6.5 g ALA per day
EPA 0.3 1.4^
DHA 1.3 1.3
EPA 0.3 0.3
DHA 0.9 1.2^
%PCP – percentage of plasma choline phosphoglycerides
%PTPG – percentage of platelet phosphoglycerides
^Statistically significant result compared to baseline

A 1992 study from India (21), in which 5 vegetarians aged 25 to 40 years old were given 3.7 g of ALA per day, showed an increase in EPA and DHA, and a reduction in LDL cholesterol and blood aggregation. See Table 7.

Table 7. Effects of ALA Supplementation: 1992 India Study
Baseline After 6 weeks of 3.7 g ALA per day
PPL (umoles/dl) PPL (umoles/dl)
EPA 0.6 2.7^
DHA 2.1 3.0^
EPA TR .4^
DHA 1.5 2.2^
LDL Cholesterol (mg/dl) 106 71^
Blood aggregation (%) 72.2 38.8^
PPL – plasma phospholipids
%PTPL – percentage of platelet phospholipids
TR – trace amount
^Statistically significant result compared to baseline

In summary, it appears that 3.7 grams of ALA per day is needed for vegetarians to see an effect in blood DHA percentages in the short-term. But, there isn’t any research in which participants were asked to cut their LA intake at the same time that they increased ALA intake. So we don’t really know if doing that would boost DHA levels in the blood or other tissues.

Non-vegetarian Conversion Rates

In order to figure out what the ALA to EPA/DHA conversion rates are for vegetarians, it may be particularly important to stick with studies that use actual vegetarians rather than meat-eaters who might have a dietary source of EPA and DHA. But because there is a lack of long-term studies on vegetarians, we should look at some of the research on meat-eaters.

There have been many studies on meat-eaters’ conversion rates, and for the most part, they have shown good conversion rates of ALA to EPA, but very little to DHA. Because small amounts or short terms do not appear to be promising, I will limit my review to two studies that used larger amounts and longer time periods.

A 2008 study on meat-eaters from Canada (22) who took 1.2, 2.4, and 3.6 g ALA per day for 12 weeks resulted in an increase in the percentage of EPA in red blood cell fatty acids for the 2.4 and 3.6 ALA groups, but no increases in DHA. This study used an intention to treat method, which means that subjects who did not comply with the regimen were still included in the results. I’d like to know the results only for the people who stuck with the regimen, but there was little information given on the level of compliance.

A 1999 study on Japanese (23) elderly subjects gave them 3 g ALA per day and reduced the omega-6 to omega-3 ratio to 1:1. After 3 months, there was no difference in EPA and DHA levels, but after 10 months, EPA levels had risen from 2.5 to 3.6% of serum lipids, and DHA levels rose from 5.4 to 6.4% (both findings statistically significant).

Welch et al. (24) reported that non-fish eaters (both vegetarians and meat-eaters) convert ALA to long chained omega-3s at a slightly greater rate than do meat-eaters, so conversion rates of vegetarians might be greater than these studies on meat-eaters show.

In summary, it appears that 3 g (the equivalent of about 1-1/2 teaspoons of flaxseed oil) per day of ALA cannot increase blood percentages of DHA in three months time, but can increase blood percentages in 10 months time, assuming intake of omega-6 is low.

Low Omega-6 to Omega-3 Ratio Foods

Table 8 lists foods with the lowest omega-6 to omega-3 ratios.

Table 8. Foods with Lowest Omega-6 to Omega-3 Ratios
Food n-6:n-3 ratio ALA
flaxseeds 1:4 1.6 g / tablespoon
flaxseed oil 1:4 2.5 g / teaspoon
chia seeds 1:3 5 g / oz
camelina oil 1:2
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.

More information on omega-3 sources can be found in the articles The Fatty Acids and Omega-3s Part 3—Plant Sources.

Whole Foods Market has a helpful summary, Cooking Oils.

DHA Supplementation in Vegetarians

A 2014 study from the USA (39) gave 46 vegans, selected on the basis of having low omega-3 status, a daily dose of 172 mg DHA and 82 mg EPA for 4 months. Percent of total red blood cell fatty acids went from about .6% to .8% for EPA and from about 2.3% to 3.25% for DHA.

In a 2009 review paper (29), Sanders describes a placebo-controlled, randomized trial from the UK in which 39 vegan men supplemented with 200 mg of DHA per day for 3 months and increased the proportion of DHA in plasma by 50% (from about .8 to 1.3% of plasma lipids).

A 2006 double-blinded, placebo-controlled, trial from Germany (35) gave 87 female and 27 male vegetarians 940 mg of DHA per day for 8 weeks. Plasma phospholipids went from 2.8% yo 7.3% DHA.

A 2006 single-blinded, randomized, placebo-controlled trial from Taiwan (36) gave 27 postmenopausal vegetarian women 2,140 mg of DHA per day for 6 weeks. LDL fatty acid composition went from 1.4% to 3.7% DHA.

A 2000 trial from Chile (4) gave vegetarians 700 mg EPA and 700 mg DHA for 8 weeks. Plasma fatty acids went from 1.1 to 3.0% DHA.

A 1996 double-blinded trial from Canada (2) gave 1,620 mg of DHA to 12 male and 12 female vegetarians per day for 6 weeks. Serum phospholipids went from 2.4% to 8.3% DHA, and platelet phospholipids increased from 1.2% to 3.9%. A 1997 study from the same researchers (1), and same dose and length, increased serum phospholipids from 2.1% to 7.1% DHA, and increased serum platelet phospholipids from 1.1% to 3.4% in vegetarians.

These studies measured DHA as a percentage of lipids, rather than absolute amounts. Table 4 shows a DHA lipid percentage amount of 4.1% plasma choline phosphoglycerides, 2.8% plasma phosphoglycerides, 2.1% platelet phosphoglycerides, 2.6% plasma fatty acids, and 1.55% platelet phospholipids.

What levels of percentage of fatty acids should vegans aim for? If you average the percentages in the paragraph above (multiplied by the number of participants), you get an average of 2.0%. And if you average the vegans’ DHA levels, you get 1.1%.

200 mg per day raised vegan DHA levels .6%. 300 mg can then be expected to raise vegans’ DHA levels .9%, taking them from an average of 1.1% to 2.0%. It thus seems reasonable to recommend 300 mg per day for the average vegan to match the same level as the average omnivores. But since it is not clear that vegans need DHA levels equal to omnivores, taking 200-300 mg every 2 to 3 days could be adequate insurance while not costing nearly as much.

Anecdotal reports have found some older vegans to have very low DHA levels, so supplementing with 200 – 300 mg per day is prudent for people over 60.

A 60 year old, male, long time vegan forwarded his fatty acid lab reports to me. In August 2012 his EPA levels were .3% and DHA was 1.0% (of fatty acids in blood). He had been using “a lot of” canola oil but it apparently wasn’t increasing his EPA and DHA levels. After six months of daily supplementation of 320 mg DHA plus 130 mg of EPA (one capsule of Ovega-3 vegan supplement), his EPA levels went to 1.0% (about average for omnivores) and DHA to 4.8% (towards the higher average range for omnivores). It appears that this regimen was adequate.

Retroconversion of DHA to EPA

A 1996 Canadian study (2) showed an 11 – 12% conversion rate of DHA to EPA after 6 weeks of 1,620 mg of DHA in vegetarians. See Table 9 for more details showing that EPA levels increased.

Table 9. Conversion of DHA to EPA: 1996 Canadian Study
Baseline 6 weeks of 1.62 g DHA per day
EPA 0.57 1.3
DHA 2.4 8.3
EPA 0.21 0.58
DHA 1.2 3.9
Thrombogenic risk factors No differences
%SPL – percentage of serum phospholipids
%PTP – percentage of platelet phospholipids
^statistically significant from baselines

A 1997 Canadian study (1) of vegetarians and meat-eaters showed a conversion rate of 9.4% of DHA to EPA from a dose of 1,620 mg DHA per day for 6 weeks, with no differences between groups.

A 2000 trial from Chile (4) gave vegetarians 700 mg EPA and 700 mg DHA for 8 weeks. DHA went from 1.1 to 3.0%. EPA went from .2 to 1.8%

A 1996 French study (3) fed three people 123 mg of DHA one time and found a conversion rate to EPA of 1.4%.

I could not find any other studies looking at DHA amounts less than 700 mg per day.

Health Benefits and Concerns of ALA

There have been numerous studies that have shown benefits of a high ALA intake and a few that have shown potential problems. Here is a quick review of those areas.

Heart Disease

A meta-analysis of five prospective studies of ALA intake published in 2004 (7) suggested that high ALA intake was associated with reduced risk of fatal heart disease (relative risk 0.79, .60-1.04). This finding was not quite statistically significant. The average highest level of intake was 2.0 g per day versus the lowest of .8 g per day.

Prostate Cancer

In contrast to the findings on heart disease which have been fairly consistent in favor of a modest benefit, higher ALA intake and blood levels have been associated with a higher risk of prostate cancer in a number of studies, and not associated in a number of other studies.

A 2004 review concluded, “More research is needed in this area before it can be concluded that there is an association between alpha-linolenic acid and prostate cancer.” (26)

A 2009 systematic review and meta-analysis (11) said:

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 (34).

Are Trans Fats the Culprit?

A 2018 study provides an interesting explanation for the contradictory results seen in earlier studies (44).

This study, part of the Health Professionals Follow-Up Study from Harvard School of Public Health, followed close to 50,000 men from 1986 to 2010 and asked them about their diet and the occurrence of prostate cancer over that time.

During the study period, trans-fat was removed from the list of food additives “generally recognized as safe,” resulting in a large decrease in the food industry’s use of trans-alpha-linolenic acid. Also during the study period, widespread screening for PSA began. This test allows for earlier detection and treatment of prostate cancer.

In the early years of the study, alpha-linolenic acid was associated with an increased risk of advanced prostate cancer. Later, after trans-alpha-linolenic acid was no longer being added to foods and PSA screening was common, a higher intake of alpha-linolenic acid was no longer associated with a higher risk of advanced prostate cancer. Perhaps, only trans-alpha-linolenic acid increases risk of advanced prostate cancer.

Another possibility is that PSA screening is identifying prostate cancer earlier before it becomes advanced. The authors say, “If ALA only increases risk of a subset of lethal prostate cancers that is curable by treatment, the onset of widespread PSA screening could have largely removed the subset of lethal cancers through curative treatment, leaving only those incurable lethal cancers unrelated to ALA.”

Based on this study’s results, it doesn’t appear necessary for men to limit their intake of alpha-linolenic acid from foods. The study did not examine high doses of alpha-linolenic acid like those found in dietary supplements.


There have been four studies looking at age-related eye damage and ALA. For age-related macular degeneration, the study using a better marker of ALA status showed it to be protective. For cataracts-related markers, the studies show that a higher intake of ALA is associated with an increased risk.

Age-Related Macular Degeneration

A 2001 analysis (14) of men and women in the Nurse’s Health Study over age 50 found that those in the highest fifth of ALA intake (about 1.5 g per day) had an increased risk of age-related macular degeneration (AMD) compared to the lowest intake (about .77 g per day; 1.41, 1.00-1.98). Total fat, saturated, monounsaturated, and trans fat were all associated with an increase in AMD. In contrast, the highest intakes of DHA tended to be protective. The fourth quintile of animal fat was also associated with a statistically significant increase in AMD (1.36, 1.03 – 1.79). The authors state:

To evaluate further the association with linolenic acid, the major food sources of this fatty acid were examined (Table 5). These foods provided 38% of linolenic acid intake in women and 46% in men at baseline. Of the food sources of linolenic acid, intake of beef, pork, or lamb as a main dish appeared strongly positively related to AMD. More than 1 serving/wk of beef, pork, or lamb as a main dish was associated with a 35% increased risk of AMD compared with <3 servings/mo (pooled RR: 1.35; 95% CI: 1.07, 1.69). A high intake of margarine was also significantly related to an increased risk of AMD. Because these food items were also major contributors of trans unsaturated fat, we adjusted further for quintiles of trans unsaturated and other fats in models with linolenic acid; the relation with linolenic acid was slightly attenuated but remained significant (Table 4). Other high-fat foods were not associated with risk of AMD (data not shown).

In contrast, a 2013 study from France (6) found that higher ALA levels in the blood were associated with a lower risk of late AMD (.62, .43-.88 per 1 standard deviation increase in plasma ALA). The results were adjusted for age, gender, smoking, educational level, physical activity, HDL, trigylcerides, CFH Y402H, ApoE4, and ARMS2 A69S polymorphisms, and follow-up time.

I would consider plasma levels in the blood a more accurate measure of ALA status than intakes, because intakes are much harder to measure independently of other fatty acids. Given that this study found that higher levels of ALA were associated with a decreased risk of late AMD, it provides some confidence that the finding from the Nurse’s Health Study was a matter of confounding.

Although the study from France used a better marker for ALA status, it was conducted by people who have received compensation from a variety of pharmaceutical companies, was smaller in number and shorter in duration than the Nurse’s Health Study, and measured only late-AMD. It would be nice to see a few more studies before drawing any strong conclusions.


A 2005 analysis (12) of a group of women from the Nurse’s 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. Interestingly, neither total fat, animal fat, vegetable fat, saturated fat, nor trans fats were associated with an increase in lens opacity. 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 (13) 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. In this case, no other fat category was associated with an increase, including total, animal, vegetable, saturated, monounsaturated, polyunsaturated, trans, LA, arachidonic acid, or long chain omega-3s.

ALA and Eyesight: Conclusion

In the case of age-related macular degeneration, it seems unlikely that raw ALA from plant foods can cause a problem. Unfortunately, the analyses of lens opacity and nuclear density did not show any correlation with animal fat and so it is hard to dismiss all of these findings as simply confounding. Until more research is performed, it might be prudent not to consume large amounts of ALA.

The studies finding ALA to be linked with eye problems were all done on only one population by one group of researchers, measuring intakes rather than blood levels. I consider it likely that further studies will show inconsistencies and until plant and/or uncooked sources of ALA are examined, I am skeptical that uncooked, plant sources of ALA are harmful to the eye.

According to the Canola Council, canola oil should be safe for use in cooking. Based on the results of the above studies on eye lens damage, make sure you use low heat and limited cooking times when cooking with canola oil until more is known about ALA and eye damage.

DHA and Prostate Cancer

In July of 2013, a study surfaced suggesting the 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 err on the lower side of the recommendations here. More details can be read in the article, DHA Supplements and Prostate Cancer.

Summary of Omega-3 Benefits and Concerns

What we know about ALA is summarized in Table 11.

Table 11. Omega-3 Recommendations
Grams per day
ISSSFAL recommendations 2.5 (F), 3.0 (M)
Vegetarian intakes 1.2 (F), 1.8 (M)
Additional amounts needed for conversion to DHA 3 – 3.7
Protective against heart disease 2
Possibly cause eye problems 1.25 – 1.5
Teaspoon of flaxseed oil 2.5
F – female, M – male

If it weren’t for the (small chance) for potential eye problems, I’d suggest either adding 3 g of ALA per day or taking DHA supplements. Because of the eye issues, that much ALA is not worth the risk when DHA supplements are available. I would still recommend adding about .5 g of ALA per day for its own benefits for heart disease and to help increase EPA levels. If using such small amounts of uncooked, plant sources of ALA the risk to the eyes should be minimal.

If you are getting the recommended ALA and DHA, EPA should not be a problem. Fish contain about twice as much DHA as EPA (27), so it’s not unusual to get more DHA than EPA in the diet. But it’s okay to get a supplement with EPA and DHA in it. If you get a DHA supplement with EPA in it, choose one with at least 200 mg of DHA per serving; I have no recommendations for how much EPA it should contain.

Recommendations to keep vegans about on par with fish eaters can be found at Daily Needs.

Vegan DHA and EPA Supplements

You can find a tremendous number of vegan DHA and EPA supplements by doing a Google search. I’m not able to assess whether any given company is better than another.


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44. Wu J, Wilson KM, Stampfer MJ, Willett WC, Giovannucci EL. A 24-year prospective study of dietary α-linolenic acid and lethal prostate cancer. Int J Cancer. 2018 Jan 8. [Epub ahead of print]

Also Reviewed

Chong EW, Kreis AJ, Wong TY, Simpson JA, Guymer RH. Dietary omega-3 fatty acid and fish intake in the primary prevention of age-related macular degeneration: a systematic review and meta-analysis. Arch Ophthalmol. 2008 Jun;126(6):826-33.

Craddock JC, Neale EP, Probst YC, Peoples GE. Algal supplementation of vegetarian eating patterns improves plasma and serum docosahexaenoic acid concentrations and omega-3 indices: a systematic literature review. J Hum Nutr Diet. 2017 Dec;30(6):693-699. The six studies included in this review are all summarized in DHA Supplementation in Vegans.

Hooper L, Thompson RL, Harrison RA, Summerbell CD, Ness AR, Moore HJ, Worthington HV, Durrington PN, Higgins JP, Capps NE, Riemersma RA, Ebrahim SB, Davey Smith G. Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review. BMJ. 2006 Apr 1;332(7544):752-60. Epub 2006 Mar 24.

Kornsteiner M, Singer I, Elmadfa I. Very low n-3 long-chain polyunsaturated fatty acid status in Austrian vegetarians and vegans. Ann Nutr Metab. 2008;52(1):37-47. Epub 2008 Feb 28. 10:1 n-6/n-3 for vegetarian diets and lower LC n-3 levels. (Abstract only.)

Kris-Etherton PM, Hill AM. N-3 fatty acids: food or supplements? J Am Diet Assoc. 2008 Jul;108(7):1125-30. (No abstract available.)

Mangat I. Do vegetarians have to eat fish for optimal cardiovascular protection? Am J Clin Nutr. 2009 May;89(5):1597S-1601S. Epub 2009 Mar 25.

Muskiet FA, Fokkema MR, Schaafsma A, Boersma ER, Crawford MA. Is docosahexaenoic acid (DHA) essential? Lessons from DHA status regulation, our ancient diet, epidemiology and randomized controlled trials. J Nutr. 2004 Jan;134(1):183-6.

Wang C, Harris WS, Chung M, Lichtenstein AH, Balk EM, Kupelnick B, Jordan HS, Lau J. n-3 Fatty acids from fish or fish-oil supplements, but not alpha-linolenic acid, benefit cardiovascular disease outcomes in primary- and secondary-prevention studies: a systematic review. Am J Clin Nutr. 2006 Jul;84(1):5-17.

Williams CM, Burdge G. Long-chain n-3 PUFA: plant v. marine sources. Proc Nutr Soc. 2006 Feb;65(1):42-50. Review.

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