Cardiovascular Health is Close to My Heart

Heart disease is one of our three biggest killers (along with cancer and stroke).  One of the better prospective studies done on vitamin D and heart disease followed subjects over time, measuring vitamin D levels and following them to see who developed a first incidence of heart attack.  They found that those with low vitamin D levels who also had high blood pressure (a well-recognized risk factor for heart disease) were more likely to develop a first heart attack than hypertensive patients with higher vitamin D levels.

These data are intriguing, but because low vitamin D levels and heart disease are both very common, and because this was not an interventional study, it is difficult to draw firm conclusions, other than more research is probably warranted.

Other studies of the effects of low vitamin D are more problematic. Vitamin D has been convincingly correlated with all-cause mortality, with certain cancers, and with multiple sclerosis.  But causation is very difficult to attribute in these cases.  Vitamin D deficiency is common in people with poor diets (including obese people) and in people who are relatively inactive.  These are independent risk factors for mortality, heart disease, and some cancers.  And while some cellular mechanisms have been discovered that may lend plausibility to a vitamin D hypothesis, there are as of yet no convincing data that allow us to draw conclusions about vitamin D and these diseases.

Low vitamin D levels are quite common, and it is nearly impossible to attain adequate levels with diet alone.  We know that vitamin D is necessary to prevent rickets, and that, combined with calcium, it is needed to prevent osteoporosis.  We do know that sun exposure will ensure an adequate level of vitamin D and because of a clever regulatory mechanism, will never result in excess vitamin D.  But we do not know what a “safe” level of sun exposure is.  We know that the relationship between sun exposure, photoaging of the skin, and skin cancers is dose-dependent, but we don’t know where to place the fulcrum in balancing the need for vitamin D and the risk of cancer.

Supplementation is effective in raising vitamin D levels, but we do not yet know what an “optimum” level of vitamin D is, and we don’t know what the long-term effects of supplementation may be.  Other fat soluble vitamins have been found to actually increase the risk of cancer if supplemented too aggressively.

The vitamin D story is fascinating, and despite over a century of study, it is still playing out.  While we can draw some pretty safe conclusions about the prevention and treatment of some common bone diseases, it is too early to form any useful conclusions about other diseases such as cancer, influenza, or multiple sclerosis.  Given our limited knowledge, recommendations on screening and treatment for vitamin D deficiency in reasonably healthy people are neither clear nor final.  We have a set of plausible and interesting hypotheses to work with, and now we need some randomized controlled trials to give us data we can really use.

PalMD is an internal medicine physician who blogs at White Coat Underground.