A study conducted in France shows that elderly men and women experience significant blood pressure changes as outdoor temperatures rise and fall, with higher blood pressure readings often seen in cold weather.

Higher blood pressure in the winter months could increase risk for stroke or other vascular events, warn Dr. Christophe Tzourio, of the French national research institute INSERM in Paris, and colleagues in a report published today in the Archives of Internal Medicine.

On the other hand, lower blood pressure during summer months places elderly individuals at increased risk for fainting, falls, or heat-wave related death.

In a population-based study of blood pressure changes among 3470 men and 5331 women, aged 65 years or older, Tzourio's group noted blood pressure measurements decreased in spring and summer, and increased to peak levels during winter.

Over the course of 13 months, the systolic blood pressure reading — the top number in blood pressure readings that represent pressure while the heart contracts — differed by 8 millimeters of mercury in the coldest versus the warmest outdoor temperature periods.

"This is a huge difference," Tzourio told Reuters Health. The effect is even stronger in the oldest individuals, he said.

For example, an outdoor temperature drop of 15 degrees Centigrade (59 degrees Fahrenheit) was associated with a systolic blood pressure increase of 5.1 millimeters of mercury among people aged 80 and older, but only a 0.8 millimeters of mercury increase among those aged 65 to 74 years old.

In contrast, an outdoor temperature increase of 15 degrees Centigrade was associated with a systolic blood pressure decrease of 13.8 and 9.9 millimeters of mercury in the oldest and the youngest participants, respectively.

Overall, high blood pressure was detected in 33.4 percent of participants during winter versus 23.8 percent during summer.

These findings highlight the importance of seasonal monitoring of blood pressure medications among elderly individuals, the investigators conclude.