People with HIV who had lower blood levels of vitamin D were more likely to have early signs of cardiovascular disease than HIV-positive people with normal vitamin D levels, according to a study published online January 27 in the journal Clinical Infectious Diseases.

Vitamin D has captured a great deal of research interest in recent years, both for people with and without HIV infection. For people who are HIV negative, large studies have tied abnormally low vitamin D levels to a number of health problems. For people who are HIV positive, at least one study has also demonstrated that vitamin D deficiency is associated with an increased risk of diabetes. This finding was ominous, as it suggested that other health complications prevalent in HIV-negative people with vitamin D deficiency, such as cardiovascular disease, may also be more likely to occur in HIV-positive people with low vitamin D levels.

To explore this point, Andy Choi, MD, from the University of California at San Francisco (UCSF), and his colleagues compared vitamin D levels and measurements of the thickness of the carotid artery—a way of testing for cardiovascular disease risk—in 139 HIV-positive people enrolled in the UCSF Study of the Consequences of the Protease Inhibitor Era cohort.

The average age of the participants was 45, most were male, and about one third were black. Roughly 75 percent were receiving antiretroviral (ARV) therapy at the time of their examinations, of whom three quarters had a viral load under 1,000 copies.

In all, Choi's team found that 52 percent of the participants had low blood levels of vitamin D. When accounting for a variety of factors, the team found that women and African Americans were more likely to have low vitamin D levels, as were those with high body mass index (BMI), which is a ratio of height to weight. People who took non-nucleoside reverse transcriptase inhibitors (NNRTIs) also had a higher likelihood of vitamin D insufficiency, but only for the first six months after starting treatment. People who took vitamin D supplements were less likely to be insufficient.

Choi and his colleagues also found that vitamin D levels also predicted arterial thickness. One way of assessing cardiovascular disease risk is by looking at the thickness of the wall of the carotid arteries, which run down the inside of the throat. Using an ultrasound machine, researchers measure the thickness of the artery to generate a figure known as the carotid intima-media thickness (cIMT). People with a higher cIMT are at higher risk of heart attacks and strokes.

In this study, Choi's team found that the greater the deficiency of vitamin D, the higher the cIMT. In fact, after adjusting for traditional cardiovascular disease risk factors such as smoking or cholesterol levels, researchers found that people with low vitamin D levels had carotid arteries that were 0.13 millimeters (mm) thicker than those with normal vitamin D levels.

“These differences in cIMT may carry important cardiovascular risk implications,” state the authors, “because in the general population, the…risk of stroke is increased by 18 percent and the risk of [heart attack] is increased by 15 percent per 0.10 mm increase in cIMT.”

Fortunately, unlike a number of other cardiovascular risk factors, vitamin D insufficiency is easy to measure and simple and inexpensive to remedy. In fact, experts recently issued new recommendations for the proper intake of vitamin D for the average person. The new guidance recommends doses of up to 600 international units per day for people up to the age of 70. It will take further study, according to Choi's team, to understand when and how much people with HIV should supplement their vitamin D levels.

“Although these findings need to be replicated prospectively in a larger cohort of HIV-infected persons, they provide evidence to support a study of vitamin D supplementation to reduce cardiovascular risk in HIV-infected persons,” the authors conclude.