The belief that vitamin D deficiency causes people to develop heart disease during winter is now being challenged by a latest study conducted by the University of Dundee.

Hugh Tunstall-Pedoe, professor emeritus at Dundee, led a team of researchers in investigating the potential connection between the cardiovascular disease and death and the lack of exposure to sunlight known as hypovitaminosis D.

The role of vitamin D deficiency in the development of winter disease was first studied in 1981, with the founding of Ninewells Hospital's Cardiovascular Epidemiology Unit.

As part of the Scottish Heart Health Study, thousands of men and women had their blood tested and measured for risk factors. The status of their health was then monitored through their medical records.

Blood samples taken from the participants were sent to Germany to be tested for vitamin D in an international project funded by the European Commission and the Medical Research Council.

While the rate of cardiovascular incidents did not vary seasonally, the findings show that deaths related to heart disease and other causes did.

The researchers also found that even though the levels of vitamin D varied during the test, with the highest levels measured in the month of August and the lowest was in March, this was observed several weeks after the incidence of winter deaths had peaked. This means the changes in vitamin D levels occurred far too late to be considered the cause of the deaths.

Another finding revealed that participants with lower vitamin D levels were more likely to suffer from cardiovascular disease compared to others, but the reduction of vitamin D levels could also be associated with the individual's lifestyle and other risk factors.

Even when the researchers corrected the condition in participants, the levels of vitamin D only had a trivial effect.

People who had low vitamin D levels did not experience an increase in risk for winter disease compared to other participants.

"This is a major study, in a population with two-to-one seasonal changes in vitamin D, and low levels overall," Tunstall-Pedoe explained.

"If vitamin D deficiency were a major cause of heart disease and death, we would have expected it to show up. But it did not."

Tunstall-Pedoe added that the results of their study serve as a challenge to this perceived role of vitamin D deficiency. He also urges other researchers to study the effects of seasonal change as well.

The University of Dundee-led study is featured in the International Journal of Epidemiology.

Photo: Suzanne Schroeter | Flickr