Evidence links low vitamin D levels with increased risk of death

I have written more than once about the benefits of sunlight. There is, for instance, quite a body of evidence which links sun exposure and the heightened vitamin D levels in the body this tends to bring with a reduced risk of cancer. It’s one major reason why, although I avoid burning, I seek the sun whenever the opportunity arises.

There is mounting evidence that cancer is not the only condition that sunlight may protect against. In quite recent times evidence has been emerging which links vitamin D with cardiovascular conditions such as heart attacks and strokes too. Some research that may be relevant to this association has found that individuals with low vitamin D levels were much more likely to suffer from hypertension (high blood pressure) compared to individuals with high vitamin D levels in the body. One mechanism which may explain this concerns the fact that vitamin D suppresses the activity of the hormone ‘renin’ ” high levels of which can cause raised blood pressure.

Earlier this year, one of my blog posts reported on a study which found that low vitamin D levels were associated with a significantly increased risk of cardiovascular disease in people assessed over a 5-year period [2]. These associations were found even when other factors that at traditionally thought to affect cardiovascular risk (such as physical activity) were accounted for. See here for more on this study.

Very recently, other similar evidence has come to light. This research, published in the Archives of Internal Medicine, looked at the relationship between blood levels of two forms of vitamin D in the body (25-hydroxyvitamin D and 1,25-dihydroxyvitamin D) and overall risk of death and risk of death due to cardiovascular disease in more than 3000 men and women followed for almost 8 years.

Compared to those with the highest levels of 25-hydroxyvitamin D in their bodies, those with the lowest levels were found to be:

At more than twice the risk of death

At more than twice the risk of death due to cardiovascular disease

These associations were found even though certain ‘confounding’ factors such as pre-existing cardiovascular disease and levels of physical activity had been taken into account.

Now, so-called epidemiological studies of this nature cannot be used to show for sure that vitamin D (and sunlight exposure) reduced the risk of death from cardiovascular disease. One study that would help to determine the true relationship between vitamin D and risk of death would be to give compare death rates in vitamin D supplemented individuals with those in individuals taking placebo over (preferably) long periods of time. The authors of this study have suggested such studies should be done.

Interestingly, the Archives of Internal Medicine published last year a ‘meta-analysis’ which grouped together several studies where overall risk of death was measured in those supplemented with vitamin D (dosages ranged from 300 ” 2000 IU per day) and compared to the death rate in individuals taking placebo. The vitamin D supplemented individuals overall were found to enjoy a small (7 per cent) but statistically significant reduction in risk of death.

References:

1. Forman JP, et al. Plasma 25-Hydroxyvitamin D Levels and Risk of Incident Hypertension. Hypertensio. 2007 Mar 19 [Epub ahead of print]

2. Wang TJ, et al. Vitamin D deficiency and risk of cardiovascular disease. Circulation 2008 Jan 7 [Epub ahead of print]

3. Dobnig H, et al. Independent Association of Low Serum 25-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D Levels With All-Cause and Cardiovascular Mortality. Arch Intern Med. 2008;168(12):1340-1349

4. Autier P, et al. Vitamin D supplementation and total mortality. Arch Int Med 2007;167:1730-1737