Researchers say a growing body of evidence suggests that vitamin D deficiency increases the risk of heart disease and is linked to other, well-known heart disease risk factors such as high blood pressure, obesity, and diabetes.
For example, 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.
"Vitamin D deficiency is an unrecognized, emerging cardiovascular risk factor, which should be screened for and treated," says researcher James H. O'Keefe, MD, director of preventive cardiology at the Mid America Heart Institute in Kansas City, Mo., in a news release. "Vitamin D is easy to assess, and supplementation is simple, safe and inexpensive."
Most of the body's vitamin D requirements are met by the skin in response to sun exposure. Other less potent sources of vitamin D include foods such as salmon, sardines, cod liver oil, and vitamin D-fortified foods like milk and some cereals. Vitamin D can also be obtained through supplements.
Vitamin D Deficiency on the Rise
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 (associated with hardening of the arteries). It also alters hormone levels to increase insulin resistance, which raises the risk of diabetes.
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.
"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," says O'Keefe. "A little bit of sunshine is a good thing, but the use of sunscreen to guard against skin cancer is important if you plan to be outside for more than 15 to 30 minutes of intense sunlight exposure."
Testing for Vitamin D Deficiency
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.
Researchers recommend 25(OH)D screening for those with known risk factors for vitamin D deficiency including:
- Older age
- Darkly pigmented skin
- Reduced sun exposure due to seasonal variation or living far from the equator
- Kidney or liver disease
The U.S. government's current recommended daily allowance (RDA) for vitamin D is 200 international units (IU) per day for individuals under age 50. For those between 50 and 70, 400 IU per day is recommended, and for those over age 70, the RDA is 600 IU. Most experts believe these doses are too low, and that somewhere between 1,000 and 2,000 IU of vitamin D per day is necessary to maintain adequate vitamin D levels. The safe upper limit of vitamin D consumption is 10,000 IU per day.
Vitamin D supplements are available in two different forms: Vitamin D2 and Vitamin D3. Although both appear effective in raising vitamin D blood levels, Vitamin D3 supplements appear to result in a longer-lasting boost.
Although there are no current guidelines for restoring and maintaining healthy vitamin D levels in people at risk for heart disease, for those who are vitamin D deficient, the researchers recommend initial treatment with 50,000 IU of vitamin D2or D3 once a week for eight to 12 weeks, followed by maintenance with one of the following strategies:
- 50,000 IU vitamin D2or D3 every 2 weeks
- 1,000 to 2,000 IU vitamin D3 daily
- Sunlight exposure for 10 minutes for white patients (longer for people with increased skin pigmentation) between the hours of 10 a.m. and 3 p.m.
Once maintenance therapy has been initiated, rechecking 25(OH)D blood levels is recommended after three to six months of ongoing supplementation.
"Restoring vitamin D levels to normal is important in maintaining good musculoskeletal health, and it may also improve heart health and prognosis," says O'Keefe. "We need large, randomized, controlled trials to determine whether or not vitamin D supplementation can actually reduce future heart disease and deaths."