Myth: Our Needs for Vitamin D Can Be Met By Sunlight
Though not really a vegetarian myth per se, it is widely believed that one's vitamin D needs can be met simply by exposing one's skin to the sun's rays for 15-20 minutes a few times a week. Concerns about vitamin D deficiencies in vegetarians and vegans always exist as this nutrient, in its full-complex form, is only found in animal fats which vegans do not consume and more moderate vegetarians only consume in limited quantities due to their meatless diets.
It is true that a limited number of plant foods such as alfalfa, sunflower seeds, and avocado, contain the plant form of vitamin D (ergocalciferol, or vitamin D2). Although D2 can be used to prevent and treat the vitamin D deficiency disease, rickets, in humans, it is questionable, though, whether this form is as effective as animal-derived vitamin D3 (cholecalciferol). Some studies have shown that D2 is not utilized as well as D3 in animals and clinicians have reported disappointing results using vitamin D2 to treat vitamin D-related conditions.
Although vitamin D can be created by our bodies by the action of sunlight on our skin, it is very difficult to obtain an optimal amount of vitamin D by a brief foray into the sun. There are three ultraviolet bands of radiation that come from sunlight named A, B, and C. Only the "B" form is capable of catalyzing the conversion of cholesterol to vitamin D in our bodies and UV-B rays are only present at certain times of day, at certain latitudes, and at certain times of the year. Furthermore, depending on one's skin color, obtaining 200-400 IUs of vitamin D from the sun can take as long as two full hours of continual sunning. A dark-skinned vegan, therefore, will find it impossible to obtain optimal vitamin D intake by sunning himself for 20 minutes a few times a week, even if sunning occurs during those limited times of the day and year when UV-B rays are available.
The current RDA for vitamin D is 400 IUs, but Dr. Weston Price's seminal research into healthy native adult people's diets showed that their daily intake of vitamin D (from animal foods) was about 10 times that amount, or 4,000 IUs. Accordingly, Dr. Price placed a great emphasis on vitamin D in the diet. Without vitamin D, for example, it is impossible to utilize minerals like calcium, phosphorous, and magnesium. Recent research has confirmed Dr. Price's higher recommendations for vitamin D for adults.
Since rickets and/or low vitamin D levels has been well-documented in many vegetarians and vegans, since animal fats are either lacking or deficient in vegetarian diets (as well as those of the general Western public who routinely try to cut their animal fat intake), since sunlight is only a source of vitamin D at certain times and at certain latitudes, and since current dietary recommendations for vitamin D are too low, this emphasizes the need to have reliable and abundant sources of this nutrient in our daily diets. Good sources include cod liver oil, lard from pigs that were exposed to sunlight, shrimp, wild salmon, sardines, butter, full-fat dairy products, and eggs from properly fed chickens.