The risk of heart attack, stroke, heart failure and other cardiac events could be predicted by measuring levels of two vitamin D components, suggest researchers from the Intermountain Medical Center Heart Institute in Salt Lake City, UT.

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Low levels of total and bioavailable vitamin D may predict poor cardiovascular health, say researchers.

Lead researcher Dr. Heidi May, a cardiovascular epidemiologist at the Institute, and colleagues found that individuals with low levels of both total vitamin D and bioavailable vitamin D were more likely to experience poor cardiovascular outcomes.

Bioavailable vitamin D is vitamin D that has been absorbed into the bloodstream but has not attached to surrounding proteins.

The researchers recently presented their findings at the American College of Cardiology Scientific Sessions in Chicago, IL.

To reach their results, Dr. May and colleagues analyzed the vitamin D levels of 4,200 individuals aged 52-76. Of these, around a quarter had diabetes and around 70% had coronary artery disease.

The team focused on measuring the participants’ levels of various vitamin D metabolites – elements of the vitamin that are produced during metabolism – and assessed whether they were associated with future cardiac events.

The researchers explain that only 10-15% of total vitamin D has the ability to act on target cells during metabolism; most vitamin D metabolites are attached to vitamin D binding proteins.

The team says it is important to assess the proportion of these “unbound” vitamin D metabolites – such as bioavailable vitamin D – that is available to pursue target cells.

From their analysis, the researchers found that measuring both total levels of vitamin D and levels of bioavailable vitamin D demonstrated the highest accuracy for predicting the risk of cardiac events.

In other words, individuals with low levels of both total vitamin D and bioavailable vitamin D were at greatest risk for heart attack, stroke, heart failure and even cardiovascular death, compared with people whose levels of these vitamins were high.

Commenting on the results, Dr. May says:

This study is the first research that evaluates the association of vitamin D metabolites with cardiovascular events. And evaluating usable vitamin D could mean the difference on the amount of vitamin D prescribed, if it’s prescribed at all.”

The researchers say their findings build on previous research associating low vitamin D levels with poor heart health. However, they call for future studies to further investigate this link in non-white populations, noting that past studies have shown the effects of vitamin D metabolites vary between white people and those of other ethnicities.

Last November, Medical News Today reported on a study suggesting that vitamin D levels below 15 ng/mL are associated with poor heart health.

And another study published last year suggested vitamin D supplements may improve exercise performance and reduce the risk of heart disease.