SciTech

Controversy stirs over Vitamin D

Credit: Alexander Moser/Art Staff Credit: Alexander Moser/Art Staff

The Institute of Medicine (IOM) released recommended dietary intake values for vitamin D and calcium last November based on already-published research and evidence. While the IOM’s report does not substantially change the recommended intake of calcium, it does elevate the recommended intake values for vitamin D. The report now suggests that the average adult consume about 1,000 and 600 milligrams per day of calcium and vitamin D, respectively. This updated vitamin D intake is an increase of 50 percent from the 1997 recommendations.

Both vitamin D and calcium have been strongly connected to the promotion of healthy bone growth and maintenance. Too little calcium and vitamin D have also been shown to result in poor maintenance of bone health, which provided the evidence justifying the increased recommendations for both nutrients. According to the IOM’s report, “The current evidence, however, does not support other benefits for vitamin D or calcium intake.” Nevertheless, the report notes that too much calcium has been associated with a number of complications, the most common of which is kidney stones. The report did not suggest a similar complication associated with excessive consumption of vitamin D.

Thus far, the suggested calcium intake levels have not caused much controversy due to the substantial amount of evidence for health problems when calcium consumption falls short or is in excess. However, there is some debate around the report’s discussion and conclusions on vitamin D. Authors Ian R. Reid and Alison Avenell, researchers from the University of Auckland in New Zealand, state that they are for the most part in agreement with most of the report’s intake values and conclusions in their article “Evidence-Based Policy on Dietary Calcium and Vitamin D.” They do, however, clarify that what most people know as vitamin D — and what is treated as vitamin D in the report — is not the active component responsible for bone health. Vitamin D is actually converted to the hormone 25-hydroxyvitamin D, also known as 25(OH)D, which is responsible for influencing bone growth and health.

Reid and Avenell also take issue with the report’s recommendation to avoid sun exposure. They emphasize in their article that “sunlight exposure is a normal part of people’s life, and that the implication that it should be universally avoided is without an evidence base.” Indeed, vitamin D is derived from UV exposure in addition to diet. Reid and Avenell see a complication in releasing a recommended intake value for vitamin D when its primary source is variable depending on the amount of sun exposure a person receives.

Reid and Avenell’s contentions with the report, however, are minor when compared to the opinions released by Creighton University researchers Robert Heaney and Michael Holick in their article, “Why the IOM Recommendations for Vitamin D are Deficient.” Heaney and Holick accuse the IOM of misinterpreting and neglecting several crucial trials in evaluating the necessary 25(OH)D hormone levels. They argue that a higher concentration of this hormone, and therefore a higher dosage of dietary vitamin D, is crucial for bone health.

Heaney and Holick cite several studies indicating that a sustained increased level of 25(OH)D reduced the number of fractures people received. In one study, there was a 33 percent reduction in fractures at higher 25(OH)D levels. “The fact that other trials, with less good compliance, failed to reproduce that effect does not negate the evidence of a well-conducted trial,” Heaney and Holick wrote.

The authors also argue that the recommended dietary intake value should be based on the intake that “prevailed during the evolution of human physiology.” They suggest that given our likely sun exposure, humans would have likely received two to three times the IOM’s suggested value. Their opinion is that these values should “be given the presumption of correctness, and the burden of proof must be placed on those who propose that lower intakes … are without risk of preventable dysfunction or disease.”

The IOM has not released any additional information addressing the concerns relating to its treatment, discussions, and conclusions of vitamin D.