As you’ve undoubtedly noticed, the nights are drawing in. If you’re in London this Sunday, the night will be drawing in at precisely 3:52pm, earlier than in all of 2014.
The twenty-first of December marks Winter solstice in the Northern Hemisphere, the shortest day and the longest night of the year. You’d be in good company if you couldn’t remember the last time your skin was warmed by the sun. Which could be a problem, and not just because you’re getting desperate for a holiday. Low exposure to sunshine is a prime risk factor for vitamin D deficiency, which affects 90% of UK adults each winter. Once thought to be mainly a problem for your bones, scientists increasingly implicate vitamin D deficiency as a danger to your heart.
Vitamin D is unusual among micronutrients in that we humans are capable of synthesising it in our own bodies (as opposed to vitamin C, for instance, which must be consumed in our diets). And that’s a good thing, since very few food sources contain much vitamin D. In order to be capable of making enough, however, we need to get enough sunlight.
It actually doesn’t take that much sunlight to make enough vitamin D in the summer, if the sunshine is bright and plentiful and if you’ve got fair skin—as little as 20-30 minutes two to three times per week should do the trick. Getting enough bright sunlight is obviously more difficult in the winter. It is estimated that between October and April each year, 90% of the UK does not get enough sunshine to make enough vitamin D. If you don’t get outdoors much, or if you’ve got darker skin (in which case you may need up to 10 times as much sunlight to make enough vitamin D), the problem gets trickier, and you even may be among the 16% of the UK adult population with a severe vitamin D deficiency.
But does it really matter, when so many people are clearly living with a vitamin D insufficiency and not realising it? The answer may be yes, and in ways you might not have realised. We’ve known for a long time that vitamin D is important for bone health, both for children and adults, but research is examining other ways vitamin D might be important, in areas as diverse as obesity, immune function, and cancer. While many of the studies so far have been inconclusive, the relationship between cardiovascular disease and vitamin D is particularly intriguing.
The observation starts on an ecological scale: in studies that examine whole populations, it is found that rates of cardiovascular disease and high blood pressure increase as you move further away in either direction from the equator, a finding that suggests the possibility that vitamin D deficiency could be at play. Many, but not all, observational studies show similar results: in one meta-analysis, there was a significant association between the lowest levels of vitamin D and high blood pressure over the course of 8 years, and in a recent review of 9 studies examining the relationship between vitamin D deficiency and heart events, 5 studies found that low vitamin D levels were associated with a higher risk of heart attack, stroke, and death. This accords with other recent studies, which find that those individuals most deficient for vitamin D are most likely to have cardiovascular disease and complications.
While interesting, researchers are keen to point out that the relationship isn’t completely clear: for one thing, trials in which vitamin D is administered have not been demonstrated to reduce cardiovascular events, although this may be in part because vitamin D given in trials is frequently combined with calcium. (When vitamin D is given alone, there is some limited evidence that it may be effective, and calcium is thought by some scientists to contribute to heart disease).
Future trials, including a large 20,000 person trial currently underway that is examining the role of vitamin D supplementation on cancer and heart disease outcomes, may help elucidate the relationship between vitamin D and heart disease.
For now, should individuals take vitamin D to prevent heart problems? Scientific and clinical bodies suggest a cautious approach until evidence becomes clearer. However, if you’re in the 90% of UK adults who is vitamin D deficient, supplements would be advisable in any event (a blood test can identify whether you’re deficient). Your bones will thank you, and it’s possible that your heart will, as well
Endocr Rev. Jun 2012; 33(3): 456–492.
Published online May 17, 2012. doi: 10.1210/er.2012-1000
The Nonskeletal Effects of Vitamin D: An Endocrine Society Scientific Statement
Clifford J. Rosen, John S. Adams, Daniel D. Bikle, Dennis M. Black, Marie B. Demay, JoAnn E. Manson, M. Hassan Murad, and Christopher S. Kovacs
Front Physiol. 2014; 5: 248.
Published online Jul 11, 2014. doi: 10.3389/fphys.2014.00248
Vitamin D: a critical and essential micronutrient for human health
Igor Bendik,* Angelika Friedel, Franz F. Roos, Peter Weber, and Manfred Eggersdorfer