Sleeping less than 7½ hours per day may be associated with future risk of heart disease, according to a new report.

A team in Japan monitored 1,255 people with high blood pressure for an average of more than four years, checking their sleep times, blood pressure and troubles such as strokes and heart attacks. They had an average age of 70.

Researchers said that during the follow-up period, 99 people had some sort of event, and it was more common in people who slept less than 7½ hours a night.

Specifically, the rates were 2.4 per 100 person-years for those with less sleep and 1.8 per 100 person-years for those who got more. A person-year is a statistical measure; if there were 10 people in a group studied for a year, they would accumulate 10 person-years of data in that time.

Patients with shorter sleep plus an overnight increase in blood pressure had a higher incidence of heart disease.

The researchers said doctors should consider sleep patterns when dealing with people with high blood pressure.

The study was reported in the Nov. 10 issue of Archives of Internal Medicine.