Dietary reference intakes for vitamin D – the evidence is strongest for bone recommendations
BY STEVEN K. CLINTON, MD, PhD, director of the Prostate and Genitourinary Oncology Clinic and 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 Dec. 2010, the Institute of Medicine announced new dietary reference intakes for vitamin D and calcium. It was the first change in these recommendations since they were first proposed in 1997. Unfortunately, confusion and misinformation has emerged with the new RDIs, leaving many in the public and evena some physicians unsure of the report’s actual recommendations.
First, it is worth recalling that Dispelling D’ Confusion RDIs are public-health guidelines designed to meet the needs of generally healthy Americans—97.5 percent of the population—from birth through old age. They help health officials assess the nutritional status of the U.S. population and physicians counsel patients. They provide information for nutrition labels, and they ensure that school-lunch, nursing-home and other institutional food programs are sufficiently fortified for good health.
I was one of a committee of 14 people that spent two years examining the literature, holding public forums and gathering information. We found that there has been great growth in the scientific literature related to vitamin D and calcium, and we reviewed a lot of intriguing data about 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 clinical studies, particularly over a range of doses, to determine the quantity of vitamin D needed to achieve a certain outcome—except in one instance. There is sufficient clinical trials data to show that vitamin D and calcium play key roles in bone health, and to define the vitamin D DRI. This was the committee’s most important finding.
Based on bone health, recommended dietary allowances (RDAs) for calcium range from 700 to 1300 mg per day for healthy individuals age one year and older. RDAs for vitamin D range from 600 international units (IUs) for ages 1 to 70 years, and 800 IUs for those age 71 and older. This corresponds to blood levels of 20 ng/ml of 25-hydroxy vitamin D, a serum marker of vitamin D status. 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 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 is an adequate upper limit for dietary of intake, which is double the previous amount. Higher levels can lead to health problems. Since the main function of vitamin is helping the body absorb calcium, the principle risk of high-dose vitamin D intake is hypercalcemia.
- Some human observational studies suggest that use of high-dose vitamin D over months or years is associated with higher mortality or other negative outcomes, such as an increased risk of pancreatic cancer at the highest levels.
- There was no evidence of benefit associated with high-dose vitamin D.
With no evidence of benefit, and with trends toward potential risk, the committee chose against recommendinghigher limits of vitamin D beyond the RDI.
Physicians treating patients withosteoporosis can continue prescribing pharmacologic preparations of 50,000 IUs per week for a number of weeks and then recheck the blood levels. This will help people who are truly deficient. But ingesting those levels every week for life might increase the risk of a negative outcome.
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.