Sleep not too little, not too much

Sleeping too little or too much can significantly increase the risk of mortality, according to a study conducted in Britain.

A decrease in sleep duration among participants sleeping six, seven or eight hours was associated with a 110 percent excess risk of cardiovascular mortality, said the study authored by Jane Ferrie of the university college London Medical School in London.

However, an increase in sleep duration among those sleeping seven or eight hours was associated with a 110 percent excess risk of non-cardiovascular mortality, it found.

The study focused on 10,308 participants between 35 and 55 years of age.

"In terms of prevention, our findings indicate that consistently sleeping seven or eight hours per night is optimal for health," Doctor Ferrie said in a statement.

She said mortality rates were lower in participants who first slept five to six hours or less but then reported extended hours of sleep.

Meanwhile, higher levels of mortality for those who slept more than eight hours a day imply that sleep restriction should be considered, Ferrie said.