Vitamin D deficiency is traditionally associated with bone and muscle weakness, but in recent years a number of studies have shown that low levels of the vitamin may predispose the body to high blood pressure, congestive heart failure, and chronic blood vessel inflammation leading the increased risk of heart attack.. It also alters hormone levels to increase insulin resistance, which raises the risk of diabetes. Several large studies have shown that people with low vitamin D levels were twice as likely to have a heart attack, stroke, or other heart-related event during follow-up, compared with those with higher vitamin D levels.

In a review article published in the Journal of the American College of Cardiology, researchers surveyed recent studies on the link between vitamin D deficiency and heart disease to come up with practical advice on screening and treatment. 

They concluded that vitamin D deficiency is much more common than previously thought, affecting up to half of adults and apparently healthy children in the U.S. 

Researchers say higher rates of vitamin D deficiency may be due in part to people spending more time indoors and efforts to minimize sun exposure through the use of sunscreens. Sunscreen with a sun protection factor (SPF) of 15 blocks approximately 99% of vitamin D synthesis by the skin. An hour in the sun without sunblock at the beach in mid summer will cause the skin to produce about 10,000 iu of vitamin D. 

We are outside less than we used to be, and older adults and people who are overweight or obese are less efficient at making vitamin D in response to sunlight. A little bit of sunshine is a good thing, but the use of sunscreen to guard against skin cancer is still a good idea for prolonged sun exposure.

Vitamin D levels can be measured with a blood test that looks at a specific form of vitamin D called 25-hydroxy vitamin D (25(OH)D). Vitamin D deficiency is defined as a blood 25(OH)D level below 20 ng/dL. Normal levels are considered to be above 30 ng/dL. Optimal evels are between 50 and 80ng/dL.