Vitamin D – The Sequel

By Marina Komarovsky

The sun is beginning to feel warm on your skin, the desire to do coursework seems to be on a downturn, and you keep hearing about the films that are coming out – some are new, and some are sequels, which of course won’t be as good as the originals. Every year, this is how summer arrives. But this summer there is a new spotlight on vitamin D. Although vitamin D didn’t make the Hollywood line-up, it did make the online home page of the New York Times last February and even scored an appearance on Oprah.

Summer is always the season when vitamin D status is highest – alongside dietary sources, vitamin D is made in the skin upon exposure to UV rays. But this summer, the spotlight is warranted because new research on the health benefits of vitamin D keeps coming in, and accordingly, the Institute of Medicine’s Food and Nutrition Board (FNB) is due to release new Dietary Reference Intakes (DRIs) for vitamin D by the end of the season. Surprisingly, the vitamin D sequel may even be better than the original.

The old plotline goes like this: Vitamin D was officially discovered in 1922 by E.V. McCollum. The vitamin really saved the day because at that time, many children were suffering from rickets, a deficiency disease of the bones. It was quickly decided that vitamin D should be added to milk to ensure that it gets into the diet in adequate quantities. As a result, rickets was essentially eliminated in the U.S. Acting to increase calcium absorption, vitamin D has a substantial effect on bone and scientists caught on that it can help prevent osteoporosis and resulting fractures as well as rickets. Everyone was happy, and the original film had a great ending.

Now, the sequel. Unlike most sequels, this isn’t just an artificial attempt to recreate the hype. Vitamin D has been implicated in the immune response – as Sarah Olliges explained in her February article “Vitamin D: Use it to Ward Off the Winter Blues and Flues” – by modulating T cell function, and emerging science shows links to reducing the incidence of cardiovascular disease, diabetes, and cancer as well as improving muscular strength.

But this is quite a large number of potential outcomes to consider, so as might be expected, the research is spread thin. Not only do studies address a plethora of outcomes, but predictors also vary. The idea that vitamin D may have a beneficial effect on diabetes risk, for instance, really came to fruition when higher dietary intake of vitamin D was associated with reduced rates of type II diabetes among white Americans in the epidemiological study conducted as part of the 2003-2006 National Health and Nutrition Examination Survey (NHANES). Now, scientists are looking to show causation by means of clinical trials. However, the experimental conditions vary across trials because there is argument about how much vitamin D needs to be given to study participants.

With such a range of research endeavors, it’s hard to predict where all of this will go. Regardless, some exciting conclusions may be in sight. “I think what will be learned,” expresses Dr. Susan Harris from the Bone Metabolism Lab of the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRC), “is that vitamin D has these effects on processes – like inflammation and cell differentiation – that play a role in the etiology of lots of different diseases.”

Harris is conducting a clinical trial in an attempt to understand at least a part of this complex picture. She and her team are looking at the effect of a large daily dose of vitamin D – 4,000 IU or ten times the current recommendation, to be exact – on markers of diabetes risk including insulin secretion, insulin sensitivity, and glucose control over a 12-week period. Her study focuses on adults ages forty and older and explores this association among African Americans in particular. Vitamin D is unique, Harris points out, in that diet is not the only environmental factor influencing status. Exposure to sunlight is another, and individuals with darker skin – those who are less prone to the deleterious effects of sunlight – are also less amenable to its benefits. Because darker skin does not absorb as much UV, smaller quantities of vitamin D are produced. Harris asks, can this lower baseline level – in a population that is at greater risk for type II diabetes – be sufficiently enhanced to prevent this condition?

The inconsistencies in status among different populations may certainly be stump the Institute of Medicine’s FNB as it struggles to wrap up the report. Typically, DRIs are listed for men and women of every age group, but here the factors of race as well as region of residence and – interestingly enough – BMI also come into play. The FNB aims to make recommendations for people in the U.S. and Canada, but the UV index in Florida strays far from that in northern Saskatchewan. To complicate matters further, it has been determined that obesity is a predictor of low vitamin D status. The high prevalence of this condition dictates that this information is another aspect of the issue that must be addressed.

Meanwhile, the pressure is on. After nearly two years of literature searches and discussions, the Food and Nutrition Board is due to release its report on vitamin D at the end of the summer.  The hope is that the new recommendations will lead to improvements in vitamin D status in the 50% of the U.S. population that is considered to have lower than ideal vitamin D levels; help the 10% of children who are categorized as clinically deficient; and curb the rates of heart disease, cancer, and type II diabetes. While dramatic changes may be wishful thinking, they have captured the imagination of the public – which is eager to start popping supplements, the minds of food manufacturers – who are already devising ways to incorporate vitamin D into every food imaginable, and the heads of supplement manufacturers – who feel bolstered by the 127% increase in U.S. supplement sales in 2007 and a subsequent 117% increase in just the first quarter of 2008. Everyone is in suspense, awaiting the FNB’s verdict.

“The excitement about … the health potential [of vitamin D supplements] is still far ahead of the science,” writes Tara Parker-Pope of the New York Times. Meanwhile among supplement manufacturers, “there is growing frustration that the governing rules,” or the recommendations and regulatory mechanisms, “are not keeping pace with the science,” confers Shane Starling of nutraingredients.com. This does create a film-worthy image: the manufacturers are chasing the policy makers and demanding some statements, the policy-makers are chasing the scientists begging for more concrete evidence, and the scientists are chasing after the public and yelling after them not to get so carried away quite yet. With a lot of drama and a number of potential positive health outcomes, the vitamin D sequel may be a good one.

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