Vitamin D Deficiency Associated with Increased Risk of Heart Disease

Author: Lorraine Savage

Article Date: 7/15/2008

A recent study published in the Archives of Internal Medicine found that low levels of vitamin D were associated with higher risk of myocardial infarction (MI) in men even when controlled for known risk factors for coronary artery disease. The study, “25-Hydroxyvitamin D and Risk of Myocardial Infarction in Men,” was led by Dr. Edward Giovannucci, Professor of Nutrition and Epidemiology at the Harvard School of Public Health in Boston, MA.

Vitamin D deficiency contributes to cardiovascular disease through vascular smooth muscle cell proliferation, inflammation, vascular calcification, the renin-angiotensin system, and blood pressure. Contributing to vitamin D deficiency is a person’s geographic location, such as low altitudes and high latitudes, darker skin tone, the winter season, and lack of exposure to sunlight.

Methodology

The cast-control study followed 18,225 men involved in the Health Professionals Follow-up Study. They were aged 40 to 75 years and had no prior diagnosis of cardiovascular disease at baseline. The median age was 63 years, and more than 90% were Caucasian.

Blood samples, which were taken between April 1, 1993 and November 30, 1999, were analyzed for plasma 25-hydroxyvitamin D or 25(OH)D concentrations using EDTA radioimmunoassay. The men were followed for 10 years, during which time 353 men developed nonfatal MI or coronary heart disease (CHD) and 102 had fatal attacks.

The case group consisted of men who were sedentary and overweight, consumed little alcohol, had a family history of heart disease before age 60, and had high LDL and low HDL cholesterol levels. A group of 900 men were chosen as controls for risk set sampling. They were selected in a 2:1 ratio and matched for age, date of blood collection, and smoking status.

Findings

After the men were matched only for age, time of blood collection, and smoking status, the study found that men with circulating 25(OH)D levels less than 15 ng/mL (nanograms per milliliter) were at greater risk of MI, compared with men with levels greater than 30 ng/mL. The relative risk was 2.42, with a 95% confidence interval (CI) of 1.53 to 3.84. Men with vitamin D deficiency tended to be smokers, sedentary and heavy, light drinkers, non-Caucasian, live in higher latitudes, and have a family history of MI.

25(OH)D levels at or above 30 ng/mL were considered a sufficient marker. Men with levels over 30 ng/mL were found to have roughly half the risk of MI, regardless of any other cardiovascular risk factors. Only 23% of the 18,225 group had levels above 30 ng/mL.

In a separate analysis, the subjects were matched for an additional battery of factors, such as family history of MI, body mass index, alcohol consumption, physical activity, history of diabetes, hypertension, ethnicity, region, omega-3 intake, fasting status, HDL and LDL cholesterol levels, and triglyceride levels. The results were roughly the same, with a relative risk of 2.09, and a CI of 1.24 to 3.54.

Surprisingly, when 25(OH)D levels were moderate -- falling in the 22.6 ng/mL to 29.9 ng/mL range -- men were still at a relative risk of 1.60 with a CI of 1.10-2.32. This is comparable with men with the lower 15.0 ng/mL to 22.5 ng/mL levels of vitamin D who had a risk of 1.43 and CI of 0.96-2.13.

Risk of MI due to vitamin D deficiency increased 2.1% for every 1 ng/mL increase in 25(OH)D level.

Recommendations

The study did not assess whether vitamin D deficiency caused death due to heart disease or whether increased levels of vitamin D, either through increased sun exposure or use of supplements, would reduce a man’s risk of heart disease.

The general recommended daily dose of vitamin D is 300-400 IU. Vitamin D is added to milk and fatty fish and is produced by the skin through exposure to sunlight. Based on the study, the authors recommend a dose of 3000 IU daily to push 25(OH)D levels to a high of 35.5 ng/mL. Other studies have shown that 4000 IU and up to 10,000 IU of vitamin D is not toxic. Nutrition researchers are encouraging the FDA to increase the recommended daily dose of vitamin D to 1000 IU.

In addition to CHD and heart failure, low vitamin D levels have been associated with other health issues, such as osteoporosis and fractures due to falls, strokes, diabetes, breast and colon cancer, peripheral artery disease, and overall increased pain levels.

Extensive use of sun blockers SPF 15 and higher and protective clothing may be contributing to the problem of low vitamin D absorption through sun exposure. The public is understandably cautious about the dangers of skin cancer. However, limited exposure to the sun -- only 10-15 minutes per day -- is not sufficient to put a person in danger, yet is an adequate amount of time to allow the body to produce beneficial levels of vitamin D.