Calcium and Vitamin D

By Marcus M. Reidenberg, MD, FACP
Weill Cornell CERT
Summary by Kathleen Mazor, EdD
HMO Research Network CERT

The press coverage of the National Institute of Medicine report on calcium and vitamin D focused on the conclusion that “with few exceptions, all North Americans are receiving enough calcium and vitamin D.” The report states that this is from diet with sunlight on exposed skin adding to the vitamin D in the body (1). This conclusion is certainly different from much written lately and oversimplifies what is in the lengthy report.

There are several terms used in the report that need definition. For example, the estimated average requirement, as stated in the report, is the amount of nutrient that meets the needs of only 50% of the people. It is not enough for the other 50%. The recommended daily allowance (RDA) is enough for 97% of the people. For adults, the RDA for calcium is 1000-1200 mg and for vitamin D it is 600-800 international units.

Calcium is mainly present in dairy products with vegetables and other foods contributing a small amount. The IOM report summary stated North Americans are receiving enough calcium. The report itself stated that this was because so many of us were consuming calcium supplements, not that it was all from food. Interpreting the summary of the report to mean that supplements can be stopped would lead to daily calcium intake well below the amount needed for good health.

Summary Points
  • The recommended daily allowance (RDA) for calcium is 1,000-1,200 mg.
  • Calcium in the diet comes from dairy products and a small amount from other foods. Many people, especially those who limit milk, take supplements to consume the needed amount.
  • The RDA for vitamin D is 600-800 international units.
  • Vitamin D is in fortified milk products and fatty fish like salmon or mackerel. Bare skin makes vitamin D when exposed to sunlight. People who stay inside a lot, who limit dairy products or eat very little fat get little vitamin D.
  • Many studies show that many people are vitamin D deficient.
  • Dr. Reidenberg recommends a daily supplement of 400-600 mg of calcium and 400-600 international units of vitamin D in addition to a nutritious diet.

Vitamin D is present in fatty fish such as salmon, mackerel, and tuna but one would have to consume ½ lb or more in order to have 600 i.u. Fortified milk is supposed to have 400 i.u. per quart but studies show that some mil does not have this much in it. Because vitamin D is a fat, it needs to be taken with other foods for it to be well absorbed by the body. The reason is that it must mix with the digested fats for the processes that absorb it to work. Thus, a really low fat diet impairs the absorption of Vitamin D.

Vitamin D is also made by the action of sunlight on bare skin. In northern areas, the decrease in time of sunlight on bare skin in winter causes vitamin D levels in blood to be lower toward the end of the winter from that at the end of summer. Housebound people get no direct sun on bare skin at all. Sun blockers on skin also decrease the amount of vitamin D the skin makes.

The IOM report states that a Vitamin D level in blood of 20 units is adequate. Many scientists think this is too low for optimum benefit but even if we accept this level, inadequate vitamin D is common. Most striking was a study in Italy of Vitamin D levels in 104 people over 100 years of age. Vitamin D was undetectable in 99 and was less than 8 units in the other five. 92% of these people showed biochemical effects of vitamin D deficiency (2).

A recent study at the Hospital of Special Surgery included 723 consecutive patients admitted for all sorts of orthopedic surgery. The average age was 60 and 26% were under 50. Only some were elderly with broken hips. In fact, 86 were being treated for a sports injury. 110 of these 723 people had vitamin D levels below 20, which is clearly deficient, and 81 others had levels of 20-24 (3). Another study also published in 2010 found that 70% of the general medical patients at the Univ. of Tennessee Health Science Center were deficient in vitamin D (had blood levels below 20 i.u.) (4).

Many studies show that a portion of our population, especially older people, have vitamin D levels that are too low (5,6). One problem with using the concentrations of one type of vitamin D as the measure of vitamin D adequacy is that the level is set as much by genetic factors (7) as by dietary intake. This may contribute to the arguments about what level shows adequate intake.

The IOM report generalizes from the studies about the variable and inconsistent effects of vitamin D on things other than bone that “the current evidence , however, does not support other benefits for vitamin D”. The problem with this generalization is that most of the subjects in the very large studies were not deficient in vitamin D to start. The studies really showed that people getting enough vitamin D are not helped by consuming still more vitamin D.

Conclusion

My personal view is that most of us do not get enough calcium and vitamin D in our diets for optimum health. Even the IOM report stated that the reason North Americans are receiving enough calcium is because we add a supplement to our dietary intake. A daily supplement of 400-600 mg calcium (as carbonate, citrate, etc.) when added to the dietary intake may be enough. It is not enough to produce an increase in kidney stones.

The data on vitamin D also shows that many of us, especially those of us who limit our milk, limit our sun exposure, or are a bit older, have inadequate vitamin D intake. A daily supplement of 400-600 international units along with dietary intake should prevent true deficiency in most of us and is low enough to avoid toxicity or very high serum calcium concentrations. Whether more is definitely better for all of us or just for selected individuals is not clear at this time. But what does seem clear to me at this time, using mostly data from the IOM report itself, is of that most of us eat less than the desirable amount of calcium and vitamin D in our food every day.

References:

  1. Institute of Medicine. Dietary reference intakes for calcium and vitamin D. Report Brief accesses Nov 30, 2010, available from http://www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D.aspx
  2. Passeri G, Pini G, Troiano L, Vescovini R, Sansoni P, Passeri M, Gueresi P, Delsignore R, Pedrazzoni M, Franceschi C. Low vitamin D status, high bone turnover, and bone fractures in centenarians. J Clin Endocrinol Metab. 2003 Nov;88(11):5109-15.
  3. Bogunovic L, Kim AD, Beamer BS, Nguyen J, Lane JM. Hypovitaminosis D in patients scheduled to undergo orthopaedic surgery: a single-center analysis. J Bone Joint Surg Am. 2010 Oct 6;92(13):2300-4.
  4. Long AN, Ray MM, Nandikanti D, Bowman B, et al. Prevalence of 25-hydroxyvitamin D deficiency in an urban general internal medicine practice. Tenn Med 2010; 103: 51-2.
  5. Holick MF. Vitamin D deficiency.N Engl J Med. 2007 Jul 19;357(3):266-81.
  6. Chu MP, Alagiakrishnan K, Sadowski C. The cure of ageing: vitamin D—magic or myth? Postgrad Med J. 2010 Oct;86(1020):608-16.
  7. Bu FX, Armas L, Lappe J, Zhou Y, Gao G, Wang HW, Recker R, Zhao LJ. Comprehensive association analysis of nine candidate genes with serum 25-hydroxy vitamin D levels among healthy Caucasian subjects. Hum Genet. 2010 Nov;128(5):549-56.

Posted 12/9/2010

This note can be found online at http://www.weill.cornell.edu/cert/patients/calcium_vitamin_D.html

Health information for everyone from the Weill Cornell/HSS CERT http://www.weill.cornell.edu/cert/patients/

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