Key Findings:
This review provides research that there is clear evidence that humans can convert ALA to DHA. When people do not consume oily fish, the proportion of DHA in plasma lipids does increase. The level of DHA in blood lipids are greatly augmented by dietary DHA. Questions remain as to whether ALA and long-chain n–3 PUFAs have comparable effects on cardiovascular risk factors and whether ALA and long-chain n–3 PUFAs differ with regard to risk using clinical endpoints. The authors note that DHA and EPA have pharmacologic effects only seen at high intakes (.3 g/d), well above the amounts likely to be consumed in most human diets (typically ,0.5 g/d). Despite the lack of EPA and DHA in their diets, vegetarians are at lower risk of CVD compared with omnivores.
ABSTRACT:
Plants provide a-linolenic acid [ALA; 18:3n–3 (18:3v-3)], which can be converted via eicosapentaenoic acid (EPA; 20:5n–3) to docosahexaenoic acid (DHA; 22:6n–3), which is required for normal visual and cognitive function. Dietary ALA is provided mainly b vegetable oils, especially soybean and rapeseed oils, but is destroyed by partial hydrogenation; it is also present in high amounts in walnuts and flaxseed. Dietary EPA and DHA are provided mainly by fish and so are absent from vegan diets and only present in trace amounts in vegetarian diets. Vegetarians and vegans have lower proportions of DHA in blood and tissue lipids compared with omnivores. High intakes of EPA and DHA (typically in the range of 3–5 g/d) but not ALA have favorable effects on several cardiovascular disease (CVD) risk factors and have been postulated to delay arterial aging and cardiovascular mortality, but these intakes are beyond the range of normal dietary intake. Arterial stiffness, which is a measure of arterial aging, appears to be lower in vegans than in omnivores; and risk of CVD in vegetarians and vegans is approximately one-third that in omnivores. Prospective cohort studies showed higher intakes of EPA+DHA, and less consistently ALA, to be associated with a lower risk of CVD, especially fatal coronary heart disease, but meta-analyses of randomized controlled trials of supplementation of EPA+DHA or ALA in secondary prevention of CVD showed no clear benefit. Current evidence is insufficient to warrant advising vegans and vegetarians to supplement their diets with EPA or DHA for CVD prevention. (Authors abstract)