LONDON, Jan 13: 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 in a report published on Monday.

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. High blood pressure -- defined as a systolic reading of 160 or higher or a diastolic reading above 95 -- was detected in about a third of the volunteers during winter and a quarter in summer.

On average, every person’s blood pressure fell between the initial and follow-up measurements, with the decrease strongly correlated with outdoor temperature, the researchers said.

Average systolic blood pressure was five millimetres of mercury higher in winter than in summer, they added.

“The higher the temperature at follow-up compared with baseline, the greater the decrease in blood pressure,” the researchers wrote.

The researchers said they did not know the reason for this, but thought a hormone linked to stress that is released in cold weather might raise blood pressure by speeding the heart.

The findings suggest that doctors should consider closer monitoring of elderly patients on high blood pressure medicine when the temperature falls, they added.

“The study may explain well-established seasonal variations in illness and death from stroke, aneurysm ruptures and other vascular diseases,” they wrote.—Reuters