Vitamin D helps all of us to maintain normal blood levels of calcium and phosphorus. By promoting calcium absorption, vitamin D helps to form and maintain strong bones. When we take enough Vitamin D, we prevent the skeletal diseases that weaken bones, rickets in children and its adult equivalent, osteomalacia. Vitamin D also probably helps us maintain a healthy immune system. It also seems to help regulate cell growth and differentiation. The U.S. government credits vitamin D with these uses and more.
Recent research also suggests vitamin D might help protect us from osteoporosis, hypertension, cancer, and several autoimmune diseases, according to another U.S. government. Too little vitamin D is also linked to diabetes, multiple sclerosis, rheumatoid arthritis, and breast and prostate cancer, according to the February 2006 issue of “The Johns Hopkins Medical Letter.” Not enough vitamin D also affects our mood and how well we think, according to a December 2006 research report in the American Journal of Geriatric Psychiatry.
But how much vitamin D should we be getting? Until I read a review of it in the January issue of The American Journal of Clinical Nutrition I had no idea. This was the question that kept me from writing this article until now.
The Dietary Guidelines for Americans 2005endorse up to 1,000 IU of Vitamin D for some people. These include “older adults, people with dark skin, and people exposed to insufficient…sunlight.” They need to “consume extra vitamin D from vitamin D-fortified foods and/or supplements.”
But how much is too much? The government’s answer to this question is what it calls the “upper limit” or UL. The government sets it at “25 micrograms (1,000 IU) for infants up to 12 months of age and 50 micrograms (2,000 IU) for children, adults, pregnant, and lactating women.” This is, the U.S. Institute of Medicine of the National Academy of Sciences says, “due to toxicities that can occur when taken in higher doses.”
That’s the limit of what we should take? But many doctors I know prescribe much larger doses. What gives?
The U.S. government may well now give way in the face of evidence showing the absence of toxicity in trials of much higher doses. John Hathcock of the Council for Responsible Nutrition in Washington, D.C., and three of his colleagues marshalled the evidence in the The American Journal of Clinical Nutrition article I mentioned above. This journal rarely makes free full text versions of its current articles available online, but its editors must have thought that this article was of sufficient import to make it available here.
Dr. Hathcock and his colleagues make an excellent case that a daily vitamin D dose of 250 micrograms or 10,000 IU is safe – except for people whose health is compromised, especially by renal insufficiency (kidney failure). Specifically, they reviewed the safety of the primary form of dietary vitamin D, cholecalciferol (vitamin D3) in the “well-conducted human intervention trials” that they reviewed.
We get our vitamin D from four sources, they conclude:
1. Exposure to the sun. In North America and Europe our long-term vitamin D production from the sun is unlikely to be more than 125 micrograms or 5,000 IU per day.
2. Unfortified foods. Most of us get an insignificant amount of vitamin D from these foods, about 2.5 micrograms or 100 IU per day.
3. Fortified foods. Milk seems to be the main source here. This amount of vitamin D can go as high as 10 micrograms or 400 IU.
5. Dietary supplements. Most multivitamin and mineral supplements provide about 5 to 10 micrograms or 200 to 400 IU, the article says. The recommended dose of the supplement that I prefer, Nature’s Way Alive, provides 12.5 micrograms or 400 IU of vitamin D. However, it is the ergocalciferol (vitamin D2) form, which is probably less potent.
This leaves a huge gap. We can fill it with a vitamin D supplement. Fortunately, this turns out to be inexpensive.
Personally, I just increased the amount of vitamin D that I take from 2,000 to 9,000 IU, since I am not getting out much this winter in the freezing and snowy weather in Colorado, where I live. I can’t wait for summer, when I can soak up more of the sun’s rays. And take fewer pills.