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What would you recommend for vitamin D intake, and what is a safe upper limit to keep in mind?
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A good recommendation is 2,000 IU per day for adults.
Deficiency in vitamin D has been associated with a higher risk of CVD, a number of cancers, and autoimmune disorders like multiple sclerosis and type 1 diabetes. Most of these come from observational studies, however, not controlled scientific studies. So there is only this association between these lower levels of circulating active vitamin D and these disorders.
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It’s a large leap to say that if we supplement the population that it’s going change things. Its certainly not going to be the magic bullet that’s going to cure any of these, but it will lower the risk. Therefore, I’m a believer in a higher dose. For adults, I would recommend 2,000 IU per day. I myself take 2,000 IU per day. Given that it is going to depend on latitude and other things, a good recommendation is 2,000 U.
For children, it is at 200 IU now, but it should be higher. Some of those studies show that if children obtain a higher level of vitamin D, they have a lower risk of diseases like type 1 diabetes. I would probably increase that to 400 IU daily and possibly higher. But I’m going to be a little conservative and say 400 IU for now.
With regard to the 2,000 IU for adults recommendation, that is so far from the toxic level that it will be safe. It is probably more than we need, but it is safe. Beyond that, there isn’t going to be any benefit. It’s not going to raise your plasma 25(OH)D status that much more if I said 3,000 or 4,000 IU per day. You’re still going to get a nice high level of probably 60 ng/mL to 80 ng/mL.
As for the upper limit, it’s a gray area. Ten thousand IU a day is the clinical toxic amount, but patients who are toxic with vitamin D have levels in the 100 to 300 ng/mL range. In order to get to that, you have to go up to over 100,000 U a day. You could probably slip by on 50,000 IU a day of vitamin D, but the government is going to be a bit more conservative, and the recommendations out of Washington will probably be in the range of 10,000 IU for toxicity. So at 2,000 IU a day, we’re well away from it.
Mark R. Haussler, PhD, is the Regents Professor and department head of Basic Medical Sciences at The University of Arizona College of Medicine, Phoenix.
Recommendation varies depending on blood levels.
The intake of vitamin is not as important as the blood level, because we get vitamin D not only from supplements and foods but from sunlight as well. Different people will get different amounts of sunlight, and skin color will determine how efficient one is at manufacturing vitamin D.
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The minimum blood level should be at least 32 ng/mL. Increasingly, that level is being placed between 40 and 60 ng/mL. The typical post-menopausal woman coming into a doctor’s office will have a value somewhere between 15 ng/mL and 25 ng/mL, so she is deficient by any reasonable standard and probably substantially so. If she was at 25 ng/mL, to raise her level to, say, 35 ng/mL would take about 1,000 IU per day in addition to all other inputs.
In terms of upper limits, there has never been a case of toxicity at levels below 200 ng/mL. It takes about 100 IU per day for every rise in blood levels of about 1 ng/mL, so to get all the way up to 200 ng/mL it would take 20,000 IU per day at a minimum, and probably more. Studies have been done using 100,000 IU as a single dose every three or four months, and they did not produce anything remotely like toxicity. Ten thousand IU is a very safe estimate for the tolerable upper intake level. Nobody ever needs to go that high, but it is nice to know that there is that kind of a margin of safety.
New recommendations may come soon, but the professional community is going to move ahead of the regulators. Most of the endocrinologists I’ve spoken to have bought into the fact that you need to achieve at least 30 ng/mL and probably 40 ng/mL, and they will use however much vitamin D is necessary in order to get you up there. As we gather more data, it may evolve that 30 ng/mL isn’t enough. But right now, that number will help a lot of the problem. If the vitamin D community were to say that levels have to be a minimum of 80 ng/mL, the pushback from the regulatory community would be so great that you would never make any progress at all. It is probably prudent to take a number that you’re liable to get a consensus on.
Robert P. Heaney, MD, is the John A. Creighton University Professor and a professor of medicine in the Department of Medicine at Creighton University, Omaha, NE.