A BP of 135/85mmHg may be best in summer and 140/90mmHg in winter, said lead researcher Dr Ross Fletcher, from VA Medical Center in Washington, DC.
The recommendation follows a five-year analysis of the electronic health records of 443,632 patients, aged an average of 66 years, with hypertension.
This showed a difference in BP between summer and winter, delegates were told at the annual scientific sessions of the American Heart Association (AHA) in Orlando, Florida, last week.
On average, 7.8 per cent more people had uncontrolled hypertension - defined as repeated readings of a systolic BP of 140mmHg or more or a diastolic BP of 90 or more - in the winter than the summer.
The difference was evident in populations attending 15 different hospitals across the US, regardless of local climate.
'BP needs to be measured in both extremes of seasons, especially in winter,' said Dr Fletcher.
He said a normal BP in summer did not exclude hypertension in winter.
AHA scientific sessions 4-7 November 2007, Orlando, Florida
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