Compiled by Ginny Messina, MPH, RD
Three omega-3 studies relevant to vegan nutrition have recently come to our attention. They’re summarized below and have been incorporated into Omega-3s Part 2—Research.
These studies didn’t change our recommendations for omega-3s, but they do underline the need for vegans to follow them—see Daily Needs.
Heart Rate Variability
The long chain omega-3 fatty acids DHA and EPA may impact heart rate variability. 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.
This study compared heart rate variability between a group of 23 adult vegans and 24 omnivores. As expected, the vegans had lower concentrations of DHA and EPA in both red blood cells and plasma.
While vegans had a higher overall heart rate variability over a 24 hour period, their daytime heart rate variability was lower and their heart rate was greater. The vegans also had lower levels of compounds associated with anti-inflammation activities in the body.
The researchers thought these effects might be part of the explanation for the inconsistencies seen in studies of cardiovascular disease among vegans and vegetarians. However, determining if the differences noted here were actually problematic for vegans or related to differences in omega-3 status isn’t clear from this study and would require a dietary intervention study to determine.
Brain Aging
Researchers compared DHA and EPA levels in red blood cells with risk for dementia in 1,575 adults who were part of the Framingham Study. The subjects had an average age of 67 years and were all free of dementia at the onset of the study.
Although previous research among the Framingham participants had found that plasma DHA levels were associated with lower risk for both Alzheimer’s Disease and all-cause dementia, this study looked at red blood cell levels since this measure reflects intake over a longer period of time—up to 120 days versus just a few days for plasma levels.
In this study, the lowest levels of DHA and EPA were comparable to what is typically found in vegans.
Based on MRI measures, total cerebral brain volume was lower among people with the lowest red blood cell levels of DHA and EPA compared to the highest. The researchers suggested that the difference was equivalent to approximately two years of brain aging. This was the only difference in MRI measures.
Higher red blood cell DHA and EPA levels were associated with performance in tests of visual memory, executive function, and abstract thinking but there was no relationship with verbal memory.
Depression
This was a meta-analysis of 28 randomized controlled trials looking at the effects of long chain polyunsaturated fatty acid (LC-PUFA) supplementation on reported symptoms of depression. It also looked at the effectiveness of EPA versus DHA.
In the meta-analysis, omega-3 LC-PUFA supplements were associated with reduced mean depression scores, but there were significant differences among the different studies included in the analysis.
Supplements were most effective in severe depression and bipolar disorders, and as clinical treatments for depression (as opposed to prevention). They were also effective in conjunction with other treatments such as antidepressants.
The primary finding, though, is that a higher ratio of EPA to DHA was more effective.
For example, studies using only DHA or using supplements that had more than 50% DHA were less likely to find benefits. This was more important than the total dose of omega-3s in the supplement.
But the researchers didn’t want to draw any real conclusions about this since no studies have directly compared DHA to EPA on depression.
