If a person has adequate exposure to sunlight and normal liver function, the body can produce 25-hydroxyvitamin D. However, for many people, especially those in urban environments and during the winter months, dietary supplementation may be important because they do not receive adequate exposure to sunlight. This is especially the case if living in high latitudes where there is less opportunity for sunlight exposure. Major dietary sources of vitamin D are limited to animal food. Vegans and those consuming very restrictive vegetarian diets are therefore at risk of deficiency. There have been reports of a high prevalence of rickets in children reared on macrobiotic diets . Alternative dietary sources include fortified soy milks and cheeses and vegan margarines. In some cases, a vitamin D supplement may be required, particularly in children under 2 years and lactating mothers with inadequate vitamin D intake.
n-3 Fatty Acids
Vegetarian diets can be lower in n-3 fatty acids, in particular the marine fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and higher in n-6 fatty acids (linoleic acid). a-Linolenic acid, the n-3 fatty acid found in plant foods, can be converted to EPA and DHA, but the rate of conversion is very low and can be further inhibited by a high intake of linoleic acid. These long-chain fatty acids are thought to be important for immune, cognitive, and cardiac function. Most studies show lower serum levels of EPA and DHA in vegans . Good vegan sources of n-3 fatty acids include flaxseed and flaxseed oil, canola oil, walnuts, and/or vegan DHA supplements. For adults, intake of n-3 fatty acids should be 0.5-2% of total energy intake .