Summary

Decreased levels of vitamin D are already linked to bone disease. Now researchers have shown that those with lowered levels have an increased risk of death from all causes and from heart disease.

Introduction

Previous work has shown that around half of the older population of North America does not have enough vitamin D. Reasons for this deficit include urbanization, global dimming, air pollution and a natural decline in production of vitamin D in the skin with age. All these factors relate to the need for sunlight to produce vitamin D in the body. The maximum desirable level of 25-hydroxyvitamin D (a measure of blood vitamin D levels) has been set at 20-30 ng/mL. Lower levels are linked to bone health problems, immune dysfunction and even cancer, as well as heart disease, high blood pressure and metabolic syndrome. Vitamin D has been shown to have beneficial effects on blood lipids, blood clotting and blood vessel function - which may be why lower levels increase heart risk.

The health impacts of vitamin D are thought to be mediated through 1,25-dihydroxyvitamin D, which is produced by the kidney and also from 25-hydroxyvitamin D itself. Researchers at the Medical University, Graz, Austria, therefore measured both compounds to see how levels impact on heart risk.

What was done

The Ludwigshafen Risk and Cardiovascular Health Study is looking at the influence of genetic markers and blood biomarkers on heart health. A group of 3,258 patients from this study were recruited. All had been referred for coronary angiography and the average age was 62. Levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were measured and the participants stratified according to the results.

What was found

During follow-up time of nearly eight years, there were 737 deaths, including 463 from heart disease. Those in the lower two quartiles of 25-hydroxyvitamin D levels had about double the risk for both all cause mortality and death from heart disease, compared with those in the highest quartile. Similar results were noted for 1,25-dihydroxyvitamin D. Lower levels of 25-hydroxyvitamin D were also linked to higher levels of inflammation, oxidative stress and cell adhesion - all biochemical markers for heart disease risk.

What this study means

The study does not prove that lowered vitamin D actually causes heart disease. But it does suggest that increased levels of inflammation and other biochemical factors may be the link through which vitamin D deficit harms heart health. The researchers suggest that based on the findings of this study, a serum level of 25-hydroxyvitamin D of 20 nanograms per mL or even higher could be important for maintaining general health. It looks as if 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D may have synergistic biological action that is independent of each other, the researchers say. Further research is needed to determine the role dietary intake, supplements, and sunlight could play in maintaining a healthy vitamin D level.