Taking Vitamin D supplements can improve exercise performance and lower the risk of heart disease, according to the findings of a small study at Queen Margaret University in Scotland presented at the Society for Endocrinology annual conference in Edinburgh.

Researchers gave 13 healthy adults Vitamin D supplements or a placebo daily for a period of two weeks.

The adults supplemented with Vitamin D had lower blood pressure compared to those given a placebo, as well as lower levels of the stress hormone cortisol in their urine. Previous studies suggest that Vitamin D can block the action of an enzyme which is needed to make cortisol.

A fitness test found that the group taking vitamin D could cycle 6.5km (about 4 miles) in 20 minutes, compared to just 5km at the start of the experiment. Despite cycling 30% further, the Vitamin D group showed lower signs of physical exertion.

"Our pilot study suggests that taking vitamin D supplements can improve fitness levels and lower cardiovascular risk factors such as blood pressure", said Dr. Raquel Revuelta Iniesta, co-author of the study. "Our next step is to perform a larger clinical trial for a longer period of time in both healthy individuals and large groups of athletes such as cyclists or long-distance runners.”

Around 10 million people in England have low vitamin D levels. On average, one in ten adults has low levels of vitamin D in summer, compared to two in five in winter. Because people with darker skin are less efficient at using sunlight to make vitamin D, up to three out of four adults with dark skin are deficient in winter.

"Vitamin D deficiency is a silent syndrome linked to insulin resistance, diabetes, rheumatoid, and a higher risk for certain cancers,” said lead author Dr. Emad Al-Dujaili. "Our study adds to the body of evidence showing the importance of tackling this widespread problem.”

Danish researchers recently reported that exposure to sunlight may delay the onset of multiple sclerosis (MS). Patients who spent time in the sun every day during the summer as teenagers developed the disease later in life than those who spent their summers indoors.