May 29, 2012
Alison is a Registered Dietitian specializing in health and fitness nutrition. She has
nearly twelve years of experience helping clients reach their nutrition and weight
loss goals. Do you have a question for Alison? Email us at firstname.lastname@example.org.
Q. Could you discuss the difference between supplements vitamin D2 and D3 and their effects? Some sources belittle vitamin D2 as if it were totally useless. How much D2 supplementation is adequate for vegans during the low sun months of the year in the Portland climate?
A. Vitamin D functions as a hormone in our body and is responsible for regulating over 200 genes. Low levels of vitamin D have been associated with cancer, heart disease, diabetes, and osteoporosis. Vitamin D is commonly referred to as the “sunshine vitamin,” as it is synthesized naturally in the body from sunlight exposure, which is the best source (more on this in question #2).
In supplements and in fortified foods, there are two types of vitamin D. Vitamin D3 is derived from lanolin (sheepskin and wool) or from oily fish and vitamin D2 is derived from fungi or plants. In their book, Vegan for Life, Registered Dietitians Jack Norris and Virginia Messina note, “The evidence suggests that the two types are absorbed equally well, but that blood levels of D2 decline more quickly when mega-doses are consumed.” At the smaller dose, they recommend 1000 IU per day; vitamin D2 appears to be as efficient as D3.
Many plant-based milks are fortified with vitamin D2, making them the preferred choice for vegans. However, the daily value on the nutrition label is based on 400 IU per day, so one cup of soy milk would actually contain 120 IU of vitamin D. This is where supplementation may become necessary to meet the 1000 IU per day that many health experts recommend.
Q. Some question the use of sunscreen because it prevents us from absorbing natural vitamin D. Others feel that we should wear sunscreen every time we leave the house. What are your thoughts? What type/strength sunscreen do you prefer?
A. This is a great question, especially as we enter the sunshine season here in the Pacific Northwest. Sunlight exposure is the best source for vitamin D synthesis (UVB rays). That being said, you need adequate, not excessive, sun exposure. Some sun exposure is protective against cancer, but don’t burn your skin. Adequate exposure is dependent on two conditions: skin-type and UV index.
Let’s first define what is considered adequate exposure. It is: 50-75% of your skin exposed (tank top, shorts, or swimsuit) between 10:30am-2:00pm, 3-4 times per week when your local UV index is 3 or higher.
Vitamin D synthesis can be achieved in about ten to forty minutes, depending on your skin type. If you have skin that easily burns and never tans, then you need around 10-15 minutes of exposure. If you have skin that rarely burns and rapidly tans, then you need around 30-40 minutes of exposure. If you’re somewhere in between (occasional burn and slow tan), then 20-30 minutes should be adequate. To find out your UV index, enter your zip code into this web address: http://www.epa.gov/sunwise/uvindex.html.
Regarding sunscreen, a minimum SPF 15 can block 99% of vitamin D synthesis by the skin. It’s best to get your recommended exposure time, and then lather on the sunscreen if you’re going to remain in the sun. When purchasing a sunscreen, look for one labeled “broad-spectrum”, indicating that it protects against both UVA and UVB rays. Tanning bed lamps generally contain UVA bulbs, which will not promote vitamin D synthesis.