How Much Vitamin D Is Too Much
By Joel Fuhrman, M.D. www.drfuhrman.com
The Food And Nutrition Board Recommends That You Take No More Than 2000 IUs Of Vitamin D Daily.
With many vitamin D experts advocating 4000-5000 IUs of vitamin D a day, I still think it wise to be more cautious at the present time. My advice is in direct contrast to that of the Vitamin D Council. This nonprofit organization is headed by John Cannell,M.D., a paid consultant of the Diasorin company that makes a vitamin D blood test, and funded by BioTech Pharmacol, a drug company that manufactures vitamin D.
The Vitamin D Council recommends 5000 IUs of vitamin D daily, and they claim that dosages up to 10,000 IUs are safe. They also contend that ideal blood levels are between 50 and 80 ng/mL, not the 35–50 ng/mL range that I recommend.
There have not yet been enough studies performed to guarantee that taking a daily dose of 3000–10,000 IUs from vitamin D supplements long-term is safe and more effective at enhancing life span than taking lower dosages. The small number of studies looking at these dosages are not adequate to rule out the possibility of harmful effects. I think the information from the Vitamin D Council is biased, and I caution people not to listen to their advice. At this point in the history of vitamin D science, supplementation should be given in the 1000–2000 range or something near to it, not the 5000–10,000 range. Additional vitamin D can be given if blood tests warrant it.
The Food and Nutrition Board of the Institute of Medicine recommends that you avoid supplementation greater than 2000 IUs of vitamin D daily. It is uncommon for a person to need more than 2000 IUs of vitamin D to reach adequate levels on their blood tests, but some individuals may.
Increasing supplemental intake above 2000 IUs a day should be done only with blood test monitoring and care so as not to push blood levels too high. High levels of vitamin D may exacerbate kidney stones and other calcifications in the soft tissues of the body. There is some evidence to suggest that an excessive amount of vitamin D and calcium can promote calcifications in the aging brain.6 Vitamin D toxicity induces abnormally high serum calcium levels (hypercalcemia), kidney stones, and calcification of organs such as the heart and kidneys if untreated over a long period of time. When the Food and Nutrition Board established the tolerable upper intake level (UL) for vitamin D, published studies that adequately documented the lowest intake levels of vitamin D that induced hypercalcemia were very limited, but because the consequences of hypercalcemia are severe, the Food and Nutrition Board established the previously mentioned UL recommendation of 2000 IU/day (50 mcg/day) for children and adults.
I agree with this recommendation. It makes sense to be cautious until more studies are done. While there is evidence that 2000–10,000 IUs of vitamin D daily is safe for most people, it seems prudent to keep the recommendations for most people under 2000, especially since blood tests indicate that this is sufficient for most individuals. Taking more than 2000 is certainly indicated and safe if the retested blood levels are still insufficient at this dose.
Certain medical conditions can increase the risk of hypercalcemia in response to vitamin D, including primary hyperparathyroidism, sarcoidosis, tuberculosis, and lymphoma. People with these conditions may develop hypercalcemia in response to any increase in vitamin D and should consult a qualified health care provider regarding any increase in vitamin D intake.
While there may be room for some debate when it comes to how much vitamin D is too much, there little or no debate when it comes to vitamin A. I have been telling people to avoid vitamin A supplements for more than ten years. During that time, more and more evidence has accumulated about the dangers of vitamin A. Now we know that ingesting vitamin A from supplements or cod liver oil not only can cause calcium loss, it also can block vitamin D activity in the body and exacerbate vitamin D deficiency. The benefits of vitamin D in a multivitamin can be offset if the multivitamin contains vitamin A. We know that vitamin A supplements can cause osteoporosis, but recent research illustrates an even more ominous issue—with the exception of people who are vitamin A deficient because they are starving (in a poor third world country, for example), vitamin A supplements are toxic, increasing the likelihood of dying younger by about 16 percent.7
1. Payne ME, Anderson JB, Sefens DC. Calcium and vitamin D intakes are positively associated with brain lesion in depressed and non-depressed elders. The FASEB Journal 2007:21(877):20.
2. Bjelakovic G, Nikolava D, Gluud LL, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2008;16 (2):CD00776.