Vitamin D is good for your bones. That much we know. But how much do you need?
In recent years, health professionals have been recommending more and more of it, citing vitamin D deficiency as the source of a variety of medical conditions. Studies have been contradictory and evidence confusing.
A new report released last week by the Institute of Medicine (IOM) has heightened the debate. While the review committee raised the recommended daily allowance (RDA) of vitamin D for adults and children, it also concluded that, with a few exceptions, everyone in the U.S. and Canada is already getting enough.
The IOM tripled its RDA for adults to 600 international units (IUs) and doubled the upper limits to 4,000 IUs. (See the recommendations here.)
Public health advocates who believe that receiving vitamin D at higher levels is a preventative way to fight diseases, such as cancer, diabetes and multiple sclerosis, have mixed feelings about the report’s conclusion that most Americans are receiving enough of the nutrient. Dr. Cedric Garland, an adjunct professor in the Cancer Prevention & Control Program at University of California, San Diego, said that he thinks the most exciting takeaway from the IOM’s report is the increase in acceptable upper limits of vitamin D. “As a cancer expert, finally we have a means at our disposal that could eliminate certain diseases by 40 percent,” said Dr. Garland. “We always felt we could not recommend over 2,000, but now we can recommend up to 4,000 because the IOM have determined that there is no harmful side effects up to that amount.”
To find out what people need to know about vitamin D, we spoke with members of the review committee, Dr. Christopher Gallagher, professor of medicine at Creighton University in Omaha, Neb., and Dr. Christopher Kovacs, professor of medicine in the Endocrinology, Health Sciences Centre at Memorial University of Newfoundland in Canada.
Here’s what they had to say:
1. People get vitamin D from sunlight; certain foods like fatty fish, milk, mushrooms, eggs and meat; and vitamin supplements.
Dr. Gallagher: Even brief sunlight 15 to 30 minutes a day between May and September can give 5,000 IUs a day. But dermatologists do not like this recommendation. Food provides only 200 IUs per day. However, 2 to 3 cups of milk each day will give another 100 IUs. In the winter months, I recommend 400 to 600 IUs per day.
Dr. Kovacs: The recommendations are to obtain vitamin D from food, and if that cannot be accomplished, then to use supplements. Because sunlight exposure is associated with certain risks (cancer), the IOM committee could not in good conscience “prescribe” a certain amount of sunlight exposure to obtain the necessary amount of vitamin D. But realistically many people will continue to meet all their vitamin D needs through sunlight exposure.
2. The majority of Americans and Canadians receive adequate amounts of vitamin D, the committee concluded.
According to the report, national surveys show that average blood levels of vitamin D are above the level needed for good bone health. That level, the committee said, is 20 nanograms (ng) per milliliter of blood, or 2,000 IUs per day. The exceptions might be older people living in institutions without regular sunlight or those with darker skin tones.
3. There are no proven benefits of vitamin D other than bone health, according to the report.
While low levels of the vitamin have been associated with health problems, including heart disease and some cancers, and cause symptoms like muscle aches, weakness, fatigue, bone pain, and fractures, the committee found little evidence that increasing intake of vitamin D will protect against those problems.
Dr. Kovacs: [Some associational studies, or those based on existing records of people with certain conditions] suggest that vitamin D and calcium may prevent certain diseases, [others] suggest that [levels of] vitamin D and calcium [higher than the RDA] will increase the risk of some of these same diseases. Also, in some associational studies, higher levels of vitamin D have been found to increase mortality, heart disease and certain nasty cancers such as pancreatic. In the end, the associational studies are not definitive. This is why the IOM committee concluded that the non-bone benefits are unproven and [that] ultimately large randomized studies [or those that are scientifically controlled with a random selection of patients] will be needed to determine what the true non-bone benefits and risks are of consuming higher amounts of calcium and vitamin D.
4. We are not currently experiencing an epidemic of vitamin D deficiency, and there is no evidence for the idea that we should all have the highest recommended level of vitamin D.
Dr. Gallagher: The idea was proposed by a small but vocal lobby that we had to reach a blood level for vitamin D of 30 ng, and people bought into it. This committee could find no evidence for that figure, but there was bone efficacy evidence for 20 ng [the IOM’s current recommended blood level for vitamin D]. Vitamin D at 400 IUs per day will generally get you to [a blood level of] 20 ng but it would take 2,000 IUs daily to get you to 30 ng [and would require that many people take vitamin D supplements, especially during winter months].
Dr. Kovacs: This [idea of a recommended blood level of 30 ng] caused 50 to 75 percent of people to register low on the blood test and created the impression that there is an epidemic of vitamin D deficiency. It is an artificial epidemic … [To add to this,] a number of researchers have promoted the results of their associational studies that suggest that higher levels of vitamin D lead to certain health benefits. They have erroneously or misleadingly concluded that their associational studies indicate cause and effect; i.e. that consuming more vitamin D will lead to the stated health benefit. The general public does not understand what associational studies are and that you can’t use a correlation between X and Y to conclude that X caused Y… suddenly there was a huge demand for the blood test.
5. If you are currently taking a vitamin D supplement, that’s OK.
The IOM recommends that, in practically all individuals, the average blood levels of vitamin D be at least 20 mg per milliliter for good bone health. According to Dr. Kovaks, people who have a problem absorbing the vitamin may need to take 2,000 IUs a day to achieve the recommended blood levels.
But can you take too much? According to the IOM report, very high levels of vitamin D (above 10,000 IUs per day) are known to cause kidney and tissue damage, and there is some evidence that lower levels have risks. But anything below 4,000 IUs per day is considered safe.
The bottom line: every person is different, and you should talk to your doctor about the need for a supplement.