Thursday, October 7, 2010

Vitamin D and the Heart

I read an interesting recent review article by Reddy Vanga, S et al. from the American Journal of Cardiology regarding vitamin D. I wanted to recap the paper, but first, some basics. You need vitamin D for bones and muscles and you get it in your milk, vitamins, plants, and oily fish. Most people are also able to get all the vitamin D they need by being outside in the sun for about 15 minutes a day. If you live in northern latitudes and have less sun, dietary supplementation may be necessary. If you feel you need to supplement your diet, the recommended dose varies from 400 international units (IU) to, at most, 2000-3000 international units (IU) a day. Your doctor can check your level (with a blood test) and tell you if you need more.

ATTENTION: Take caution with anyone who recommends higher doses or diagnoses a deficiency without appropriate testing and seek medical advice before taking any doses larger than these on your own. While hyper-Vitamin D is rare, it can happen and I have personally cared for a little old lady who OD'ed on Vitamin D and had dangerous derangement of her calcium level!

Back to the review. I found the review to be a valuable discussion of the cardiovascular effects of vitamin D. Not only did the authors detail the structure, function, and role vitamin D plays in a variety of cardiovascular diseases, but they succinctly summarized all the data about whether or not the science shows that replacement fixes the associated problem. This is key because it is very important to note that just because two things are associated does not mean you can fix one and expect the other to improve automatically.
  • Blood Pressure: there is evidence that vitamin D may play a role in high blood pressure through regulation of the dilation of blood vessels (low levels cause BP to go up). Vitamin D affects calcium metabolism but also apparently it can directly activate the renin-angiotensin system. There are a couple of studies showing that if vitamin D levels are low, that supplementing them can lower BP (note: if your vitamin D is normal, taking more will not help). 
  • Peripheral Artery Disease: deficiency is associated with thickening of the carotid artery, no studies have demonstrated replacement to be effective at reversing this.
  • Cholesterol: low vitamin D is associated with high cholesterol, but no studies have shown that replacement can lower cholesterol.
  • Heart failure: while low vitamin D has been associated with heart failure, one study compared heart failure patients to normal patients and showed that heart failure patients were more likely to live in urban environments with less sun exposure and less access to fitness facilities (confounders). One study of a certain type of heart failure (uremic failure caused by kidney failure) showed that the heart might beat just the tiniest bit harder with Vitamin D supplements, but no studies have shown to extend life or reduce hospitalization (improve quality of life).
  • Death: the review does not go into detail but concludes by stating that many studies show that deficiency is associated with higher risk of death and replacement can reduce that risk.
In summary then, I expect that I will check vitamin D levels on more patients and replace as needed since deficiency is largely a silent condition.

From Pubmed:

Observational studies strongly associate vitamin D deficiency with a variety of cardiovascular diseases beyond defects in bone and calcium metabolism. Vitamin D has multiple mechanisms that potentially may affect cardiovascular health. Because vitamin D deficiency is common, therapies directed at the replacement of vitamin D may be beneficial. To date however, studies evaluating vitamin D supplementation are few and have not consistently shown benefit. It is possible that the lack of benefit in these studies may have arisen from suboptimal levels of vitamin D supplementation or other unknown factors. Nevertheless, the growing body of observational data and consistent findings of relatively high rates of low vitamin D serum levels warrant further well-designed studies to investigate the relation between vitamin D and cardiovascular health. In conclusion, vitamin D is now recognized as important for cardiovascular health and its deficiency as a potential risk factor for several cardiovascular disease processes.

No comments:

Post a Comment