Researchers investigate why cold weather affects blood pressure and raises CVD risk.
Research presented at the recent European Society Congress suggests that the colder the weather, the higher the risk of heart attack (acute myocardial infarction – AMI). The findings emphasize that better knowledge of everyday risk factors might help health care providers and policy makers optimize prevention strategies
High blood pressure (BP) has consistently been associated with an increased risk of MI. This risk is associated with systolic and diastolic hypertension. The control of hypertension has been shown to significantly reduce the risk of MI.
In the study presented, researchers found that cold weather are the crucial environment triggers for AMI. They obtained weekly data on AMI patients undergoing percutaneous coronary intervention (PCI) in 32 Belgian centers between 2006 and 2009. They correlated this data with average weekly weather reports, including air pollution, black smoke, temperature and relative humidity. Results showed that only temperature significantly correlated with AMI, and that, for every 10 percent decrease in minimal temperature there was a significant 7 percent increase in AMI incidence. Air pollution had no noteworthy effect.
“Since the results related to 10 degree decreases in temperature in both winter and summer, this points not to a pure cold effect, but rather to an effect of the absolute change in temperature,” said investigator Marc Claeys. He added that potential mechanisms explaining the increased risk associated with decreasing temperature include stimulation of cold receptors in the skin and the sympathetic nervous system.
Furthermore, in cold conditions the plasma concentrations of certain clotting factors, platelet count and in vitro aggregation are all increased, thereby promoting clotting. This, together with reduced plasma volume and increased blood viscosity during cold exposure, promotes thrombosis.
“For high risk patients the clinical implications of our findings include avoidance of strong temperature changes and advice to wear suitably warm clothes outdoors when there are drops in temperature,” said Claeys.
A second study described at the same press conference and performed in seven countries confirmed that risk factors for CVD increase during the winter months. The study recruited more than 100,000 subjects aged between 35 and 80. Data included body mass index, waist circumference, systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides and glucose from ten population-based studies.
The risk factors which showed definite winter increases included SBP. Lead investigator Pedro Marques-Vidal, said that “the study suggests that particular care with CVD prevention should be taken over the winter months. It is important that emergency resources are strengthened in winter.”
He added that a possible explanation for lower blood pressure levels in summer is that higher ambient temperatures lead to vasodilation and perspiration. It is also possible that higher levels of physical activity and a different dietary intake in summer may reduce obesity.
Mortality studies are now under way to see if the seasonal effect persists.