Heart attacks and strokes are more common in the winter, and a new study published in the online version of European Heart Journal, might have found the reason why. Investigators Tim Clayton and Tom Meade of the London School of Hygiene & Tropical Medicine’s Medical Statistics Unit, have found strong evidence that recent respiratory infections increase the risk of heart attacks and strokes.

Researchers have long recognized, using information from death certificates, that there is an excess of deaths from coronary heart disease (CHD) and stroke during the winter months—even discounting those directly attributable to deaths from respiratory disease—but they needed more evidence.

Clayton and Meade applied to the British Heart Foundation for funding to enable them to undertake further research to confirm or refute the findings of previous studies based on information from general practice which showed that respiratory infections were a strong risk factor for stroke.

Using the general practice database, the IMS Disease Analyzer Mediplus database (IMS), the researchers carried out a clinical case-control study. IMS contains details of approximately 2 million patients registered with approximately 500 GPs in the UK and is widely used in epidemiological research.

The investigators found that the risk of both heart attack and stroke doubled in the week following respiratory infection, but that the risk lessened to no excess risk beyond one month. Age or gender were not risk factors, and the risk for heart attack was seen at every level of preceding risk, whether low or high.

The researchers say that the benefit of reducing respiratory infection, either through ensuring high immunization rates or by treating and preventing infection, may be substantial.

The take-away message is that anyone with heart disease should be immunized against flu, which is a serious infection that could trigger a heart attack, possibly leading to death.