Low Vitamin D, Later CVD: Not True, in Diabetes Study

Marlene Busko

April 03, 2013

Contrary to what prior research suggests, vitamin-D deficiency did not predict early signs of cardiovascular disease in an observational study of patients with type 1 diabetes.

The study, based on data from around 1200 participants from the Diabetes Control and Complications Trial /Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC), was published online March 25 in Diabetes Care.

In fact, patients in their 30s with type 1 diabetes and a vitamin-D deficiency tended to have a lower — not higher — risk for coronary artery calcium (CAC) 10 years later, when they were in their 40s. In addition, plasma levels of 3 vitamin-D metabolites were not associated with carotid intima media thickness (IMT).

These findings "should be viewed with caution," the authors write. "We're not ready to accept these results as definitive, but they're important to publish," lead author Michael C. Sachs, PhD, from the University of Washington, Seattle, told Medscape Medical News. "The bottom line is…that more research is needed to determine how cardiovascular disease, specifically coronary artery disease, develops over time."

Asked to comment on the study, JoAnn E. Manson, MD, from Brigham and Women's Hospital, Boston, Massachusetts, and director of the Vitamin D and Omega-3 Trial (VITAL), had a slightly different take on the prior work. She told Medscape Medical News in an e-mail that the new findings "aren't surprising, because the research studies to date have been inconsistent and inconclusive.

"The enthusiasm for high-dose vitamin-D supplementation is far outpacing the scientific evidence…[and] it remains far from conclusive that higher intake of vitamin D or higher blood levels of vitamin D will prevent heart disease, cancer, or other chronic illnesses," she added. Her large, randomized trial VITAL should help clarify the effect of vitamin D on cardiovascular disease; results are not expected until 2016 or 2017, however.

Could Findings Be Due to Youth of Trial Participants?

Patients with type 1 diabetes often have premature atherosclerosis, and some studies have suggested that the atherosclerosis may be partly due to impaired vitamin-D metabolism, Dr. Sachs and colleagues write.

They analyzed plasma samples obtained around 1992, from 1193 participants in the DCCT — about equal numbers of men and women who had had type 1 diabetes about 7.5 years and had a mean age of 32 years.

They determined plasma levels of 3 vitamin-D metabolites: 25-hydroxyvitamin D, a measure of vitamin-D intake; 1,25-dihydroxyvitamin D, a measure of vitamin-D activity; and 24,25-dihydroxyvitamin, a measure of vitamin-D turnover.

About 10 years after these blood tests, the participants underwent computed tomography imaging to measure CAC.

They also had B-mode ultrasonography scans in 1994 and again about 6 years later to measure changes in internal and common carotid artery IMT.

Even after adjustment for multiple confounders, there was no link between levels of vitamin-D metabolites and subsequent signs of subclinical cardiovascular disease.

According to Dr. Sachs, these conflicting results could be due to the current study population being young and relatively healthy, apart from their type 1 diabetes. So they were perhaps not old enough to manifest atherosclerosis, he suggested.

This study was supported by grants from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The authors have disclosed no relevant financial relationships. Dr. Manson has  disclosed no relevant financial relationships.

Diabetes Care. Published online March 25, 2013. Abstract