LONDON (Reuters) – Cold weather may raise old people's blood pressure and increase the risk that they will suffer stroke, heart attack or kidney failure, French researchers said this week.

Previous research has shown that blood pressure changes with the seasons, but few studies have looked specifically at old people, Annick Alperovitch of the National Institute of Health and Medical Research in Paris and colleagues said.

"Although our study does not demonstrate a causal link between blood pressure and external temperature, the observed relationship nevertheless has potentially important consequences for blood pressure management in the elderly," they wrote in the Archives of Internal Medicine.

High blood pressure, or hypertension, can lead to stroke, heart failure, heart attack and kidney failure. It affects more than a billion adults worldwide. The French team looked at the relationship between blood pressure and temperature in more than 8,800 men and women aged 65 or older. The volunteers were from three cities and had their blood pressure measured at regular intervals in 1999 and again two years later.

Both systolic and diastolic blood pressures differed across the four seasons and during varying outdoor temperatures.