THURSDAY, Dec. 29, 2005 (HealthDay News) -- Hot weather can play havoc with blood pressure, sending it up in seniors and down in the middle-aged, a new Italian study shows.
For those over 65 who have hypertension, hot nights translate into higher blood pressure readings, but for younger patients, "physicians should reconsider reducing blood pressure medication in the summer," said lead researcher Dr. Pietro Amedeo Modesti, an associate professor of internal medicine at the University of Florence. That's because pressure for patients under 65 tends to fall in the summer.
The findings suggest a need to adjust patients' medications when the weather changes, the researchers conclude in the current issue of Hypertension.
Modesti's team tracked the 24-hour blood pressure of more than 6,400 people, average age 59, in Milan and Florence over a 14-month period. They then correlated those measurements with round-the-clock weather reports.
When the weather was hot, with daytime temperatures from 78 to over 90 degrees, daytime systolic blood pressure -- the higher number in a 120/80 reading -- was significantly lower than on cooler days, the researchers found.
Hot nights were associated with significantly higher blood pressure in people over 65, but not in younger people.
"We did not have information on the air temperature inside people's homes, but in Italy air conditioning is not widely used," Modesti added.
The study also found that the number of different drugs for blood pressure control taken by the older people was significantly lower on hot days (average 1.71) than on cold days (2.3). The researchers found no such relationship for people under 50.
The information should be taken into account when planning trials of blood pressure treatment, Modesti said.
"If you enroll patients into a drug trial without considering the season, you could introduce bias," he noted.
The study is interesting but hardly conclusive, said an American expert, Dr. Daniel Jones, dean of the University of Mississippi School of Medicine and a spokesman for the American Heart Association.
The study was "observational," meaning that it did not control for outside factors that might affect the results. "So the link is very early in terms of an association," Jones said.
If the finding holds up, it might eventually have an effect on medical practice, Jones said. "There might be some products designed to be given at night or be released at night," he said.
But at the moment, the study, while it explores "an intriguing research issue that deserves follow-up, would not change medical practice at the present time," Jones said.
Find out more about high blood pressure at the American Heart Association.