Vitamin D

by Reed Mangels, PhD, RD
From Simply Vegan 5th Edition

Summary: Vitamin D is not found naturally in the vegan diet but can be made by humans following exposure to sunlight. At least 10 to 15 minutes of summer sun on hands and face two or three times a week is recommended for adults so that vitamin D production can occur. Food sources of vitamin D include vitamin D fortified soy milk and rice milk, and mushrooms that have been exposed to ultraviolet light.

Vitamin D is essential for calcium absorption. Failure to obtain enough vitamin D is associated with bone disease in both adults and children. The vegan has no natural, reliable source of vitamin D in the diet. However, this should not be used to argue that we were meant to eat meat. Meat does not contain vitamin D either. In fact, the only significant naturally occurring sources of vitamin D are egg yolks and fatty fish. Mushrooms also contain limited amounts of vitamin D. The vitamin D content of mushrooms can be increased by commercial exposure to ultraviolet light. Vitamin D is added to cow’s milk and butter in the USA.

Vitamin D is unique among the vitamins because we can get it in other ways besides through diet. Vitamin D is first activated in the skin upon exposure to sunlight. It goes on to the liver and then to the kidneys where it is converted into the form of vitamin D that regulates bone formation.

Adequate exposure to sunlight, 10 to 15 minutes of summer sun on hands and face two to three times a week, is recommended for adults to obtain adequate vitamin D (1). This recommendation is estimated from studies in infants. Those with darker skin and the elderly (2,3) seem to require longer exposure to sunlight. In the winter months, above latitude 40 degrees N and below 40 degrees S, our skin does not activate vitamin D (4). Sunscreens (5) and air pollution also reduce the amount of vitamin D produced.

Food sources of vitamin D for vegans include some vitamin D fortified breakfast cereals, and vitamin D fortified soy milk and other non-dairy milks. Ergocalciferol, or vitamin D-2, is made on a commercial scale from yeast (6) and is used to fortify some foods. A vegan vitamin D-3 has been recently developed. If you cannot spend time outside routinely and your diet does not include some of these vitamin D sources regularly, a vitamin D supplement is needed. Current recommendations for vitamin D are 15 micrograms (600 IU) for adults 19 through 70 years and 20 micrograms (800 IU) for those 71 and older (7).

References

1. Specker BL, Valanis B, Hertzberg V, et al. Sunshine exposure and serum 25-hydroxyvitamin D concentrations in exclusively breast-fed infants. J Pediatr 1985;107:372-376.

2. Clemens TL, Henderson SL, Adams JS, Holick MF. Increased skin pigment reduces capacity of skin to synthesize vitamin D3. Lancet 1982;1:74-76.

3. Holick MF. McCollum Award Lecture, 1994: vitamin D: new horizons for the 21st century. Am J Clin Nutr 1994;60:619-30.

4. Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: Exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab 1988;67:373-378.

5. Matsuoka LY, Ide L, Wortsman J, et al. Sunscreen suppresses cutaneous vitamin D synthesis. J Clin Endocrinol Metab 1987;64:1165-1168.

6. Bartas J-M. Vegetarian Journal’s Guide to Food Ingredients. Baltimore, MD: The Vegetarian Resource Group, 1997.

7. IOM (Institute of Medicine). Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academies Press, 2011.

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