Vitamin D was first linked with excess winter disease in 1981, the same year that the Cardiovascular Epidemiology Unit in Ninewells Hospital in Dundee was launched to study causes of the excess heart disease in Scotland. Thousands of healthy men and women agreed to have risk factors measured, blood taken for testing, and their medical records followed, in the Scottish Heart Health Study.
Recently their saved blood has been tested for vitamin D in Germany, in a Medical Research Council and European Commission-funded international project. Results were related to intervening illness and death. They show that while overall incidence of cardiovascular events did not vary seasonally, deaths from heart disease, and from other causes, did. Vitamin D levels also varied, with highest levels seen in August and lowest in March – a two-to-one difference – but crucially this was several weeks after peak winter death rates, so changes in vitamin D were too late to be the cause.
People with lower vitamin D levels did have higher rates of cardiovascular disease, but low vitamin D levels were also associated with lifestyle and other risk factors. When these were corrected for, vitamin D levels had a trivial or no additional effect. People with low vitamin D levels did not have a greater increase in winter disease rates compared to others.
Emeritus Professor Tunstall-Pedoe, who initiated and still leads the Scottish Heart Health Study, said, “This is a major study, in a population with two-to-one seasonal changes in vitamin D, and low levels overall. 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. So our results seriously challenge its alleged role. We want others to explore seasonal change as we have done – a huge natural experiment which comes for free.
“All of this was made possible by the co-operation of healthy Scottish volunteers, by continuing access to their records, and by Scottish, United Kingdom, and European Commission funding at different times over many years. It benefitted from national and international collaboration.”
Emeritus Professor Hugh Tunstall-Pedoe ‘retired’ at age 65 in 2005 but continues researching on his studies in an honorary capacity. With his statistical colleague, Mark Woodward, he developed the ASSIGN cardiovascular risk score for Scotland, launched in 2007 and based on the Scottish Heart Health Study. This incorporates the standard risk factors but also social deprivation and family history. These factors were used in this latest study in testing whether vitamin D made any additional contribution – it did not.
Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation, which part funded the research, said, “We’ve known for many years that a low level of vitamin D is associated with an increased risk of cardiovascular disease, but it was not clear whether lack of vitamin D directly causes the increased risk or is a consequence of other factors. The long-term Scottish Heart Health Study, which the BHF helped to fund, has provided a series of valuable insights over the years and they have now shown that that low vitamin D is result of other risk factors, rather than a cause of increased risk.
“The research team were able to use the large seasonal variation in vitamin D levels in the Scottish population in their study, which strongly supports the conclusions from other independent genetic studies.”