Middle-aged adults who get too little sleep are more likely to develop high blood pressure, U.S. researchers said on Monday.

    The study, among the first to directly measure sleep duration in middle-aged adults, found missing an average one hour of sleep over five years raised the risk of developing high blood pressure by 37 percent.

    It also suggests that poor sleep may explain in part why black men have higher blood pressure risks.

    "People who didn't sleep as much were at greater risk of developing hypertension over five years," Kristen Knutson of the University of Chicago reported in the Archives of Internal Medicine.

    Adults typically need between seven and nine hours of sleep, according to the U.S. Centers for Disease Control and Prevention, but many get far less, and several studies have begun to show the health consequences.

    In children, lack of sleep has been shown to raise rates of obesity, depression and high blood pressure. In older adults, it increases the risk of falls. And in the middle-aged, it raises the risk of infections, heart disease, stroke and cancer.

    The team studied 578 adults with an average age of 40. They took blood pressure readings and measured how long each person slept. Only 1 percent slept eight hours or more.

    The volunteers slept six hours on average. Those who slept less were far more likely to develop high blood pressure over five years. And each hour of lost sleep raised the risk.

    "If you compare six hours of sleep to five hours of sleep, the five-hour sleepers will have 37 percent greater odds of developing hypertension," Knutson said.

    The team also found that men, and particularly black men, got much less sleep than white women in the study, who were least likely to develop high blood pressure.

    "These two observations suggested the intriguing possibility that the well-documented higher blood pressure in African Americans and men might be partly related to sleep duration," Knutson and colleagues wrote.

    Overall, the findings were not explained by sleep apnea, a dangerous type of snoring that is known to raise blood pressure risks. "Poor quality sleepers had higher blood pressure risks regardless of whether or not they snored," Knutson said.

    There were some sex differences, however.

    Knutson said getting less sleep had the same effect in men regardless of whether they snored. But women who snored had even greater odds of developing high blood pressure.

    It is not clear why, but Knutson said snoring is more rare in women and may be more strongly linked with sleep apnea.

    Knutson said studies need to be done to see if helping people sleep more can cut the risks of developing high blood pressure, which affects a third of Americans and contributes to 7 million deaths worldwide each year.