Women who regularly get fewer than 7 hours of sleep each night may have a higher risk of developing high blood pressure, a new study suggests.

British researchers found that among more than 10,000 adults who were followed for five years, women who routinely slept for 6 hours or less were more likely than their well-rested counterparts to develop high blood pressure.

Compared with women who said they typically got 7 hours of sleep a night, those who logged in 6 hours were 42 percent more likely to develop high blood pressure, while those who routinely slept no more than 5 hours had a 31 percent higher risk.

There was, however, no clear relationship between amount of sleep and blood pressure among men, the study authors report in the journal Hypertension.

The findings suggest there may be a “gender-specific” relationship between sleep deprivation and high blood pressure, according to the researchers, led by Dr. Francesco P. Cappuccio of Warwick Medical School in Coventry.

The exact reason for the finding is unknown.

A number of studies have linked poor sleep quality to an increased risk of high blood pressure, diabetes and heart disease. Much of this research has focused on people with the breathing disorder sleep apnea, but some evidence suggests that sleep deprivation, in the absence of any overt sleep disorder, also takes a health toll.

For their study, Cappuccio and his colleagues used data from a long-term health study of 10,300 white British civil servants between the ages of 35 and 55 years old.

The researchers focused on participants who were free of high blood pressure in the 1997-1999 phase of the study and were reassessed in 2003-2005. During these two phases, 76 percent and 68 percent, respectively, of the original group were included the evaluations.

At reassessment, 20 percent of the study participants were newly diagnosed with high blood pressure, and the risk was greater among women who were “short sleepers.”

Risk factors for heart disease - such as smoking, being overweight or having a sedentary lifestyle - did partially contribute to the relationship. However, an independent link between sleep and blood pressure still remained.

Experts speculate that sleep deprivation may contribute to high blood pressure by keeping the nervous system in a state of hyperactivity, which in turn affects systems throughout the body - including the heart and blood vessels.

According to Cappuccio’s team, more studies are needed to confirm that sleep duration, itself, affects blood pressure levels - and why these effects might be different in women and men.

SOURCE: Hypertension, October 2007.