You may have heard a lot about vitamin D in the news lately. What's all the fuss about? Researchers have known for many years that this vitamin is essential for bone health, since it assists with calcium absorption. But recent studies have shown that vitamin D acts in many other tissues of the body as well, and deficiency of this vitamin is now thought to be linked to many health problems including cancer, autoimmune diseases, diabetes and cardiovascular disease. Vitamin D deficiency is now thought to be widespread among the general population, so it is an important issue for everyone (not just vegans).
Sources of Vitamin DSunlightVitamin D is unique, in that the traditional source of this vitamin is not diet, but sunshine; your skin can synthesize this vitamin when it is exposed to UV rays. Some vitamin D can be stored by the body to allow for intermittent exposure. In this modern world, however, most of us don't spend as much time outside as we used to. And if you live above 42 degrees North latitude (a line approximately between the northern border of California and Boston), the sun’s rays are too weak in the winter to produce vitamin D. Even in the summer, many of us may not be making enough D; since sunscreen blocks UV rays, applying sunscreen before you go outside prevents vitamin D synthesis. (But, there is certainly a place for sunscreen, as it is important for preventing sunburn and reducing risk for skin cancer.)
(Photo credit: NOAA.gov)The best source of vitamin D is sunlight.
Dietary SourcesThere are also dietary sources of vitamin D. Most natural sources (fish, beef liver, egg yolks) are not vegan, but mushrooms sometimes contain D, depending on how they are grown. Their vitamin D content can vary widely, so they aren't a reliable source. Many foods are fortified with vitamin D, including cow's milk, enriched nondairy milks, cereals, and even some brands of orange juice. Compared to the amount of vitamin D that can be made when your skin is exposed to the sun for about 20 minutes (~20,000 international units or IU), the amounts found even in fortified foods are relatively small (usually around 100 IU per serving). So, despite what the Dairy Council would have you believe, milk is NOT
liquid sunshine; you would have to drink more than 12
gallons of milk (or soymilk, for that matter) to equal the amount of D your skin makes (for free!) in a mere 20 minutes.
How much Vitamin D do we need?The optimal amount of vitamin D needed is still not known. Recent research indicates, however, that the recommended daily intake of 200-400 IU is adequate for preventing overt deficiency (i.e. rickets), but is much too low for guarding against D-related chronic diseases. (As an aside, when these recommendations were made years ago, the physiological requirement for D was not known, so it was based on the amount of vitamin D in a teaspoon of cod liver oil, one of the richest dietary sources.) Because of this new evidence, the American Academy of Pediatrics recently increased their vitamin D recommendations for children from 200 to 400 IU per day. Many experts in the field believe that daily intake of 800-4000 IU in adults is best. One way to find out if you are getting enough D is to request a blood test from your primary care provider to find out if your 25-OH-vitamin D is within normal limits (>30 ng/mL or >75 nmol/L).
It is difficult to reach these amounts through diet alone, and even multivitamins only contain 200-400 IU. Most people will need a separate supplement at least during the winter months (November through February) in conjunction with sensible sun exposure during the summer. (That is, 15-20 minutes of sun on your face and hands before putting on sunscreen, 2-3 times per week.) I should note that the American Association of Dermatologists suggests that skin protection should be used every time one is exposed to sunlight to guard against skin cancer. If you are at high risk of skin cancer, supplements are the best way to get your D. But since sunlight is undoubtedly the best natural source of D (and certainly the most economical one), the benefits of
sensible sun exposure likely outweigh the risks for most people.
Vitamin D SupplementsShopping for vitamin D supplements can be a bit tricky for vegans. Two different forms of D are used for making supplements, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D2 is derived from yeast (vegan-friendly) but most D3 is derived from
lanolin (not so vegan-friendly). Though several older studies indicate that D3 may be up to three times more effective than D2 in raising and maintaining blood vitamin D levels, a
newer study shows that D2 is equally effective. Still, the best way to tell if you are supplementing at the right level is to get your blood tested (ideally during the winter) to see if your levels are in the normal range.
How Much is Too Much Vitamin D?While the current upper limit of safety for vitamin D intake is set at 2000 IU, many experts believe this is far too low. Indeed, toxicity has only been demonstrated at excessive doses (i.e. extended supplementation of 50,000 IU per day). Based on the research I have seen, I would suggest taking no more than 5000 IU of vitamin D2 during the winter months only, and getting out in the sun a few times a week in the summer.
Vitamin D During Pregnancy and Breastfeeding Vitamin D is needed for fetal growth and bone development during pregnancy. One
recent study also showed that women deficient in vitamin D were almost 4 times more likely to have a Cesarean section than those whose blood levels were adequate. It is best to supplement with
at least 1000 IU daily and to get your blood levels checked if possible. Breastmilk only contains a small amount of vitamin D (its concentration is affected by maternal levels, but is unlikely to contain enough D even if the mother's levels are adequate), so exclusively breastfed infants should take a supplement.
Vitamin D During Infancy and ChildhoodVitamin D is very important during the early years of a child's life for proper bone mineralization. A
recent review also showed a significant decrease in the risk for developing type 1 diabetes among children who received vitamin D supplements. The
American Academy of Pediatrics recently doubled their recommendations for children from 200 to 400 IU. However, even 400 IU may not be enough to maintain adequate blood levels; doses of 1000-2000 IU per day are considered safe in children. Because babies have such delicate skin, it is best not to rely on the sun for vitamin D in infants under one year old, so supplementation is the advised method. Vitamin D drops are available for babies, but the only ones I have seen are vitamin D3-based. Because this vitamin is so important, I would argue that it is still best to supplement. Look for drops that contain only vitamin D, as these are likely from lanolin (derived from wool), whereas drops that contain vitamins A, C and D may be derived from fish oil. (If anyone knows where to find vegan D2 drops for infants, please let me know!)
My Recommendations- Practice sensible sun exposure during the summer months. This means exposing the face and hands to sunlight for 20-30 minutes, before putting on sunscreen, two to three times per week.
- Take a separate vitamin D supplement during the winter, containing 1000-4000 IU of vitamin D2.
- If you can, get your 25-OH-vitamin D levels tested during the winter to see if you are supplementing enough.
- Pregnant and breastfeeding women should be sure to get enough D (1000-4000 IU of D2 daily).
- Breastfed infants should begin vitamin D supplementation of 400-1000 IU daily within the first few weeks of life. Unprotected sun exposure isn't recommended for infants under one year.
- Children and adolescents need at least 400-1000 IU's daily from a mixture of sun exposure and supplements.
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