Scitech  The vitamin D-bacle

To D or not to D. That is the question.

As a vegetarian, I am aware that there are several important nutrients that may be lacking from my diet: one of these is vitamin D. Vitamin D has long been known to be crucial for bone health. In addition to dietary sources of vitamin D, such as fatty fish and eggs, vitamin D can be synthesized in the skin upon contact with sunlight.

For the past several years, I have not given this any thought, believing, as many do, that the sun exposure I get is enough to fulfill my daily requirements. But seeds of doubt were planted within me when I left the doctor’s office with a note that had “2000 IU (International Unit) vitamin D” scrawled across it. It turns out that, according to many researchers and health practitioners, most of the population is actually vitamin D deficient. Behind this simple vitamin lays a contentious and convoluted debate that has split many scientists, doctors, and lay people into several warring factions.

The spurt of interest in vitamin D in recent years has shown vitamin D’s promise as a way to prevent or fight cardiovascular disease, prostate cancer, diabetes, multiple sclerosis, and a host of other maladies. Many physicians and other health practitioners have begun to recommend vitamin D supplements to ill and healthy people alike. In light of this, the governments of Canada and the U.S. have asked the Institute of Medicine (IOM) to assess current data and update the Dietary Reference Intakes, a nutrition guide. These values are used to – among other things – determine the percentages of vitamins and nutrients that appear on the back of a bag of chips or on a box of oatmeal. After amassing over 1000 studies concerning the effects of vitamin D and calcium on health, the ad-hoc panel will be able to resolve the problem.

Many numbers are thrown around in the massive 1132 page report. The brief states that a blood level of 20 nanograms per millilitre is the “level that is needed for good bone health for practically all individuals.” In order to achieve these levels, the IOM recommended a daily vitamin D intake of 600 IU, or 800 IU for the elderly.

Since the amount of sun exposure varies greatly from person to person and individuals are discouraged from excessive sun exposure due to the risk of skin cancer, the IOM created these guidelines assuming minimal sun exposure. However, this is often not the case, and the IOM found that sun exposure is, in fact, a substantial source of vitamin D for most North Americans.

The most important take-away message from all of these numbers is that, according to the IOM, most people are not vitamin D deficient. According to the IOM, in lieu of a standardized system for determining sufficiency or deficiency, many labs could have used inflated values, thus exaggerating the number of people who are actually vitamin D deficient. Finally, to top it all off, the IOM stated that excessive levels of vitamin D are not only superfluous, they are actually harmful to bone health.

Since the report, the IOM’s methodology has come under heavy fire from all quarters. They looked at each study and ranked thembased on reliability. Any studies that involved too small a trial group were excluded as this increases the chances of random errors, which could exaggerate misleading findings. They also excluded any studies that did not pertain directly to bone health, as the results were varied, inconclusive, and could not prove causation. Studies that were randomized and placebo-controlled trials received the highest rating.

While their reasoning is sound, there are several problems with their methods. Firstly, by focusing on only large, randomized, placebo studies, the IOM reduced their sample size from over 1000 studies to roughly 70. Second, the policy of eliminating any and all smaller experiments was opposed by many of the original researchers who felt that although the studies were small, they were valid. Finally, the IOM ignored all ecological and case-controlled studies. Ecological studies use populations as a unit of analysis while case-controlled studies compare subjects that are similar, with the exception of the condition in question. Studies like these cannot always prove causation, and, in the case of ecological studies, are often subject to an ecological fallacy: it assumes that individuals of a population have the same attributes as the population itself. However, history teaches us that the importance of these “lower grade” studies cannot be ignored; it was a case-controlled study that first suggested the link between smoking tobacco and lung cancer.

In addition to criticisms against their general methods, the IOM received criticism regarding specific calculations and studies. There are disputes over the way they calculated their ideal levels, their inclusion of a non-double-blinded study, and the use of a study involving 500000 IU of vitamin D – an outrageously high number. All of these undermine the validity of not only the IOM’s findings, but the integrity of the panel and organization at large.

Many people who disagree with the IOM are turning to the Endocrine Society, which submitted a guideline just a few months after the IOM. They state that people should aim for vitamin D blood levels of 30-60 ng/mL, levels the IOM would deem harmful.
The IOM and other organizations and experts continue to remain cautious of overly high recommendations of vitamin D. While the study involving 500000 IU of vitamin D was excessively high, it did show that the chances of falling increased even at blood levels of 40 ng/mL, which can be achieved with less than 4000 IU – the IOM’s recommended upper limit. While the Endocrine Society also recommends an upper limit of 4000 IU for daily maintenance, it suggests up to 10000 IU to correct deficiency.

The history of science gives many examples of the dangers of acting based on initial observations. In the late 50’s, thalidomide was sold as a cure for morning sickness in a number of countries around the world. It was not known at the time that thalidomide causes extreme birth defects and often even death. In the United States, Frances Oldham Kelsey of the Food and Drug Administration denied Richardson-Merell’s application, demanding further studies to be done. Even though thalidomide was already being sold in over 20 countries, including Canada, Germany, and Australia Kelsey still refused to allow thalidomide to be sold in the U.S. Six years later when the drug was finally taken off the markets Kelsey received the President’s Award and was widely regarded as a hero.

Although these kinds of incidents are rare, they can leave lasting scars.  After all, a treatment performing exactly what it promised in clinical trials is hardly newsworthy. But a treatment going surprisingly and terribly awry captivates the attention of many, especially those who make the guidelines and give permission.  When Kelsey managed to save countless lives, what lasts in the minds of policy makers is the thought that a rigidly dogmatic attitude can avert disaster.

But how can one tell how much of the IOM’s claims are playing it safe and how much of it is too definitive? Are the IOM’s calls for further studies really fueled by a better-safe-than-sorry mentality, or is it a cop-out? Is there enough evidence, even without large placebo-controlled trials that require decades, to give advice to the general public? With each day that passes, new information emerges and current Dietary Reference Intakes become more and more obsolete. The studies the IOM demands could take anywhere from three years to three decades, making it extremely difficult to arrive at a decisive result. Either way, almost all parties agree that the discussion is not over. In the meantime, I am going to try to walk a fine line – that is, the line between sunlight and shade. At least that way half of my body will be right in the end.