Atherosclerosis is a disease where plaque builds up within arteries clogging blood flow. Blockage of coronary or heart arteries leads to heart attacks, blockage of arteries to the brain leads to strokes, and blockage of arteries within the arms and legs leads to peripheral vascular disease or peripheral artery disease. Development of atherosclerosis is a complex process involving the immune cells, blood vessel endothelial cells, and smooth muscle cells within blood vessels. Fifty percent of the worldwide population is deficient in vitamin D and this deficiency is an important factor in development of cardiovascular disease. A recent review in the journal Circulation points out the importance of vitamin D in the development and prevention of cardiovascular disease.
Vitamin D protects endothelial cells lining blood vessels, reduces inflammation that can damage blood vessels, increases nitric oxide and other chemicals which relax blood vessels, and reduces damaging oxygen metabolites (free radicals).
Vascular smooth muscle cells lining blood vessels grow and migrate into the inner wall of blood vessels during atherosclerosis. Vitamin D blocks this cell growth and migration. Vitamin D also improves relaxation of these smooth muscle cells and aid in repair of stress smooth muscle cells. Vitamin D has been shown to activity of the enzyme (telomerase) that stops DNA from unwinding in these cells. Clotting within blood vessels is also decreased by vitamin D.
Immune cells (e.g. white blood cells) are affected by vitamin D. In patients who are vitamin D deficient, there is an excess of chemical released from white blood cells that cause inflammation and clotting (interferon, tumor necrosis factor, interleukin-6, interleukin-2).
There are a variety of other blood vessel protecting effects of vitamin D. These include improved insulin sensitivity. Improved insulin sensitivity is associated with a decrease in blood vessel wall thickening and a decrease in a variety of toxic metabolites that damage blood vessels. Vitamin D deficiency is associated with higher total cholesterol levels. Administration of vitamin D in those who are deficient increases HDL (good) cholesterol and decreases triglycerides. Vitamin D suppresses renin and other chemical that lead to hypertension, a risk factor for blood vessel damage and atherosclerosis.
Recently, the Institute of Medicine defined vitamin D deficiency as a 25(OH)D level less than 20 ng/ml, insufficiency as a level of 21 to 29 ng/ml, and sufficiency as a level of 30 ng/ml or higher. While they recommend vitamin D supplements for those with deficiency, they noted that deficiency was associated with worse cardiovascular health, they stated further study is needed to determine who might benefit from vitamin D supplements.