Should you skip C (calcium) and D?
You are likely aware that a committee of the Institute of Medicine has just issued recommendations for calcium and vitamin D intake. The big news is that the committee is recommending not as much more of both nutrients as enthusiasts might have hoped, and sounds a precautionary note about excess dosing.
Are the supplement enthusiasts right, and IOM wrong- or vice versa? Is the IOM report a reliable basis for your own decisions?
Let's start with the strong points -- of both the IOM in general, and this particular report. The Dietary Reference Intakes --of which the new report is a small part, and home to the RDAs -- are evidence-based. As a scientist and physician, I consider that a good thing. But it comes with caveats nonetheless.
An evidence review is only as good as the available evidence. While the IOM committee report on calcium and vitamin D refers to "1000 papers reviewed," it says nothing (at least not before accessing the fine print) about the quality of those papers. But since I know this literature fairly well, I can tell you: not great.
We simply do not have large-scale, long-term intervention trials with all the bells and whistles -- randomization, double-blinding, placebo-control -- to tell us what dose of calcium or vitamin D is truly optimal for health. The science we do have, no matter how many papers are cited, has major gaps in it which must be filled with judgment.
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The judgment of the IOM panel is sound, as are there cautious conclusions which, fundamentally, suggest that we stick close to the calcium intake previously recommended about a decade ago and not go higher, and roughly double our intake of vitamin D daily (to between 400 and 600 IU), but not more.
These cautious conclusions are based on studies that fail to show clear benefits of higher doses, and studies that suggest (but do not prove) the possibility of harm. They are also based on the prime directive of biomedicine -- "first do no harm," and its cousin, the precautionary principle. The precautionary principle basically says to take the path of least risk when in doubt -- and that is what the IOM committee appears quite reasonably to have done.
Bottom line: Haphazard fortification with the nutrients du jour-whatever they may be- is a bad idea, and always was. When this is done, there is no predicting what dose or unbalanced combinations of nutrients you may consume over the course of a day. Some judicious fortification makes sense, but when every processed food contains calcium, or vitamin D, you are indeed at risk of inappropriate doses. The IOM report rightly sounds an alarm about these prevalent and misleading practices.
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Calcium supplementation by adolescent girls and adult women may make sense, although calcium from foods including low and non-fat dairy is likely preferable. There are other therapeutic roles for calcium as well, such as treating PMS. It would be very appropriate for individualized decision making, ideally based on a discussion between each woman and her gynecologist or primary care physician.
I am less convinced by the IOM's cautious interpretation of the vitamin D literature, however. I find that many of my patients, when tested, do, indeed, have very low blood levels. Sun exposure is limited in much of the U.S. during much of the year. And while definitive evidence to support high dose vitamin D supplementation is lacking, there are hints of benefit in many studies with dosing above the IOM recommendation of 400 IU daily.
My advice about vitamin D, therefore, remains much as it was: get outdoor activity whenever possible, and let sunlight work its magic. If you can't get a good 20 minutes a day of sun exposure, dietary vitamin D is essential. It can come from fortified food, but a supplement is a very reasonable insurance policy. A supplement of 400IU daily ensures you will get the recommended dose, at least. Higher doses may be warranted, but should be discussed with your physician. You are unlikely to suffer any harm from doses up to 2000IU per day, but I hasten to add that we don't have long-term intervention trials to prove harmlessness any more than we do to prove benefit.
Calcium and vitamin D are important nutrients. As with all nutrients, enough is good- too little or too much is bad. The IOM invokes the precautionary principle to offer recommendations that are reasonable, and willfully conservative. But a relative absence of evidence means that guidance is as much about judgment as science.
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