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Dispelling D' Confusion

Debate, controversy and much media attention have left many unsure of the recommendations of a new national report on vitamin D. and calcium

By Steven K. Clinton, MD, PhD,
director of the Prostate and Genitourinary Oncology Clinic, leader of the OSUCCC – James Molecular Carcinogenesis and Chemoprevention Program, and a member of the Committee to Review Dietary Reference Intakes for Vitamin D and Calcium

In December 2010 the Institute of Medicine/National Academy of Sciences announced new dietary reference intakes (DRIs) for vitamin D and calcium. It was the first revision in these recommendations since they were first proposed in 1997. As expected, the new DRIs stimulated debate and controversy and attracted much media attention, leaving many in the public and even some physicians unsure of the report's recommendations.

First, it is worth recalling that DRIs are public-health guidelines designed to meet the needs of generally healthy Americans—97.5 percent of the population—targeting various age groups from birth through the elderly. They help health officials assess the nutritional status of the U.S. population, and they help physicians counsel patients. They provide information used for nutrition labels and ensure that school-lunch, nursing-home and other institutional food programs are composed to provide adequate nutrients for good health.

I was honored to serve on the committee of 14 academic leaders that spent two years examining the literature, holding public forums and writing the new DRIs. We found that there has been tremendous growth in the scientific literature related to vitamin D and calcium, and we reviewed intriguing data concerning the influence of vitamin D, in particular, on health outcomes involving cancer risk, frailty during aging, immune function and neurodegenerative diseases such as multiple sclerosis.

But there were too few high-quality studies, particularly randomized controlled trials over a range of doses, to determine the quantity of vitamin D needed to achieve certain health outcomes—except in one instance. There are sufficient data from a wealth of studies to show that vitamin D and calcium play key roles in bone health, and to define DRIs. This was the committee's most important finding.

Based on bone health, recom-mended dietary allowances (RDAs) for calcium range between 700 and 1300 mg per day for healthy individuals, depending upon age and gender. RDAs for vitamin D are 600 international units (IU) for ages 1 to 70 years, and 800 IU for those age 71 and older.

Since vitamin D can also be synthesized in the skin in response to sunlight, the DRIs were established to provide adequate intake in the absence of sun exposure. Blood concentrations of 20 ng/ml of 25-hydroxy vitamin D, a serum marker of vitamin D status, is a reasonable target in healthy individuals. Indeed, no clear evidence of additional improvements in bone health or other outcomes was noted for 25-hydroxy vitamin at higher concentrations. This remains one of the controversial points in the report. Other findings include the following:
• The majority of Americans and Canadians, with few exceptions, receive adequate amounts of both vitamin D and calcium through their current diet and sun exposure. Exceptions include those with poor nutrition, those living at northerly latitudes or in institutions, or those with dark skin pigmentation.
• 4,000 IUs was defined as the recommended upper level for usual dietary intake, which is double the previous amount. The new upper level recognizes the safety of vitamin D intake over a wide range, yet provides a margin of safety necessary for public health. Intakes beyond the upper level leading to very high serum concentrations of vitamin D can cause toxicity, such as hypercalcemia, and recent studies suggest that too much vitamin D may be linked to greater mortality particularly from certain cancers, or other health issues.
• The committee recommended that national standards for vitamin D serum assays be established. Modern assays with uniform methods should be adopted. In addition, the definition of normal ranges based upon the latest scientific evidence needs to be
agreed upon. Frequently, laboratory results reported to physicians and patients indicate that values between 20 and 30 ng/ml are deficient, which is not the case in otherwise healthy individuals.
• The report recognizes that individual patients monitored by physicians may need personalized recommendations for vitamin D and calcium intake to prevent or treat certain diseases. For example, physicians treating patients with osteoporosis can provide pharmacologic preparations of vitamin D and monitor the blood levels to ensure safety and optimal health outcomes.
• The committee identified crucial areas for future research. These include the potential role of vitamin D in various disease processes such as specific cancers, frailty, immune function and autoimmune diseases, cognition and cardiovascular disease. Well-designed human clinical trials with vitamin D over a range of intake levels will be necessary to establish DRIs in these areas.

For a good summary of the 2011 report on dietary requirements for vitamin D and calcium, see "The 2011 Report on Dietary Reference Intakes for Calcium and Vitamin D from the Institute of Medicine: What Clinicians Need to Know." Ross AC, Manson JE, Abrams SA, et al. J. Clin. Endocrinol. Metab. 2011 Jan; 96(1):53-8. Also, Manson JE, Mayne ST, and Clinton SK. Vitamin D and Prevention of Cancer—Ready for Prime Time? N. Engl. J. Med. 2011 {Epub ahead of print}.

 
6-Jun-11
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