How Much Vitamin D Is Enough?

Research suggests a multitude of benefits of vitamin D, but it’s reasonable to boost intake cautiously.

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I've been hearing a lot about vitamin D lately. My multivitamin has 400 IU, but I've heard reports that the recommended daily allowance is not actually high enough. What do you think?

Our bodies make vitamin D3 when we're exposed to sunlight. (This substance is more appropriately considered a hormone because it's synthesized in one location for use in other parts of the body.)

We know that vitamin D increases absorption of calcium from the intestinal tract. It also stimulates osteoblasts that remodel bone, making good healthy bone. Newer evidence suggests that vitamin D plays a regulatory role in controlling panels of genes that affect our immune systems. Higher vitamin D levels are associated with a lower risk of adult onset type 2 diabetes and autoimmune inflammatory responses against one's own thyroid gland, resulting in an underactive thyroid. D3 deficiency may be related to a number of other autoimmune disorders in which we attack a number of our own cells and glands. Vitamin D may play some role in preventing infection and in warding off cancer.

The data linking high levels of vitamin D with lower levels of cardiovascular disease may be confounded by the fact that healthy individuals who are out in the sun running, golfing, playing tennis, and swimming are deriving their cardiovascular benefits through exercise rather than through the vitamin D that they are receiving in their skin, so I would like to see more information about that. The last speaker at a Harvard/Johns Hopkins Primary Care Medicine symposium in December stated that one should consider 4,000 units of vitamin D3 to be our optimal daily intake, and he mentioned that he has almost never seen anyone taking less than 10,000 units a day develop vitamin D toxicity (which would be measured by elevated calcium levels). These generalizations do not apply to people with underlying kidney disease or certain other health situations such as sarcoidosis that might predispose them to being extra sensitive to the effects of vitamin D. Many patients quite reasonably prefer to start with a 1,000 unit capsule of vitamin D3 every day. After three to six months, we recheck the levels of vitamin D and calcium. We could raise them to 2,000, 3,000, or 4,000. Some doctors recommend giving 10,000 units every week or 50,000 units a week for several weeks, but I don't think this is as physiologic as getting a steady dose. I have seen patients become confused by their instructions and take the very high dose vitamin D tablets on a daily basis, and they have gotten into trouble.

Good studies have suggested that there is little to be gained by ingesting extra beta-carotene, vitamin C, vitamin E, folic acid, etc., but I think the data on vitamin D will hold up and we should all continue to follow the new information with great interest. I have seen many patients with chronic fatigue syndrome and fibromyalgia improve dramatically as they have begun taking 4,000 units of vitamin D3.

[Related: Why you might not need a vitamin D test. And how much time in the sun is needed to make vitamin D?]

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