To D or Not to D
Vitamin D has become the new superstar of the vitamin world. It was not so long ago that vitamin D was associated only with bone health and the prevention of rickets and osteoporosis. Over the past decade, the evidence that vitamin D plays a far greater role in health, has escalated. Research suggests that vitamin D may protect against numerous forms of cancer, heart disease, diabetes, multiple sclerosis, rheumatoid arthritis and gum disease.
Vitamin D is unique relative to all other vitamins. It is a hormone which has receptors in cells throughout the body. We are just beginning to understand the critical roles this special nutrient plays in health and disease. It impacts body cells, bones, muscles, and other hormones, and it affects the nervous system and immune system. Vitamin D can be made by exposure to warm sunshine or other sources of UV light (UV lamps). Unfortunately, for many people, exposure to sunlight has dwindled to such an extent that our vitamin D production has been seriously compromised. For people who have limited sun exposure, fortified foods and fish are the primary sources of vitamin D. In North America, cow’s milk and margarine have served as our primary vehicles for vitamin D fortification. Vegan dietary sources of vitamin D include fortified foods such as non-dairy beverages, breakfast cereals, bars and smoothie infusions, and mushrooms exposed to UV light. Unfortunately, food intakes are seldom sufficient to meet recommended intakes. In 2011, a report of EPIC-Oxford showed that vegans had lower vitamin D status than other dietary categories, although they were not deficient. The Adventist Health Study did not find a difference in vitamin D status in those with different dietary patterns.
So what is a vegan to do? Is a vitamin D supplement required? If so, is vitamin D2 a reliable source?
The first step in determining vitamin D needs is to ask yourself if you get sufficient sunshine. If you live in Los Angeles or Atlanta (around 33-35 degrees north), your vitamin D production may be inadequate from late November through early February. If you live in New York City or Boulder (around 40 degrees north), the “vitamin D winter” (period when you can’t make enough vitamin D from sunshine) extends from early November until early March. Going further north to Edmonton Canada (53 degrees north), it is likely that you are “D-fecient” from October to mid or late March. While it is true that you store vitamin D with adequate sun exposure in the summer months, there is little guarantee that it will carry you through an entire winter. Of course there are concerns about getting too much sun – wrinkles, age spots and even skin cancer. Sun exposure is a bit of a balancing act.
Most light-skinned people can make enough vitamin D with 15 minutes of warm sunshine to the face and arms or an equivalent surface area of skin each day. For people with darker skin, the time required increases to a half hour, or more. As people age, vitamin D production wanes, and by 70 years, our ability to produce vitamin D is only about 30% of what it was as a young adult. Other factors that negatively affect vitamin D production from sunshine include sunscreen, clothing coverage, overweight and air pollution.
People with limited exposure to warm summer sun are well advised to include a good source of vitamin D in their diet. For vegans, this could come from two places: dietary supplements and fortified foods.
There are two types of vitamin D commonly found in fortified foods and supplements: vitamin D2 and vitamin D3. Vitamin D2 is the form of the vitamin that is derived from plants, while vitamin D3 is derived from animal sources or lichen. It appears that taken at nutritional doses (up to 100 mcg (4000 IU) ) vitamins D2 and D3 are essentially equivalent. However, vitamin D2 is much less effective when used in extremely large boluses (e.g. 1250 mcg (50,000 IU)). Lichen-derived vitamin D3 is now widely available, so vegans can opt for this form of the vitamin if they prefer.
The recommended intake or Dietary Reference Intake (DRI) for vitamin D is 10 mcg (400 IU) for infants 0-12 months, 15 mcg (600 IU) for children and adults up to age 70 years, and 20 mcg (800 IU) for adults over 70 years. Many experts now think that these recommendations are insufficient, and suggest daily intakes of 25-50 mcg (1000-2000 IU) to minimize the risk of vitamin D-related disorders. Vitamin D can be toxic when taken in very large doses. The upper limit (UL) for vitamin D is 50 mcg (2000 IU), although many experts suggest that up to 250 mcg (10,000 IU) is safe for adults.
It makes good sense for vegans to aim for 25-50 mcg (1000-2000 IU) per day during the months that they do not get sufficient sun exposure. Some individuals may require more to achieve recommended vitamin D levels. The National Institutes of Health (NIH) considers 50 nmol/L adequate for health; some experts suggest 75 nmol/L as optimal. The NIH advises against levels above 125 nmol/L.
Few multivitamins contain sufficient vitamin D, however for those eating significant amounts in fortified foods, a multivitamin may provide enought to meet the RDA. Otherwise a single nutrient Vitamin D supplement can be used.
Food and Nutrition Board of the Institute of Medicine. Dietary Reference Intakes (for macronutrients, minerals, vitamins) Available online at: http://www.nap.edu/topics.php?topic=380.
National Institutes of Health. Office of Dietary Supplements. Vitamin D Fact Sheet for Health Professionals. Available online at: http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional
Chan J, Jaceldo-Siegl K, Fraser GE. Serum 25-hydroxyvitamin D status of vegetarians, partial vegetarians, and nonvegetarians: the Adventist Health Study-2. Am J Clin Nutr. 2009;89(5):1686S-1692S.
Crowe FL et al. Plasma concentrations of 25-hydroxyvitamin D in meat eaters, fish eaters, vegetarians and vegans: results from the EPIC-Oxford study. Public Health Nutr. 2011;14(2)340-346
Biancuzzo RM, et al. Fortification of orange juice with vitamin D(2) or vitamin D(3) is as effective as an oral supplement in maintaining vitamin D status in adults. Am J Clin Nutr. 2010 Jun;91(6):1621-6
Glendenning P, et al. Serum 25-hydroxyvitamin D levels in vitamin D-insufficient hip fracture patients after supplementation with ergocalciferol and cholecalciferol. Bone. 2009;45(5):870-5
Wacker M, Holick MF. Sunlight and Vitamin D: A global perspective for health. Dermatoendocrinol. 2013;5(1):51-108.
This is an updated version of an article written by Brenda Davis, R.D. and printed in Vegetarian Voice, a publication of the North American Vegetarian Society. Visit their website at http://navs-online.org/