New research shows that getting less sleep per night increased the risk of heart disease in people with high blood pressure.

The Japanese study, published in the Archives of Internal Medicine, reported that people who slept less than 7.5 hours per night had a 68 percent higher risk of heart attack or stroke than those with normal sleep durations.

The researchers looked at 1,255 Japanese adults with high blood pressure, for 50 months. The average age of the patients was 70.4 and scientists observed their sleep duration, daytime and nighttime blood pressure and if they had a cardiovascular incident such as a stroke, heart attack and/or a sudden cardiac arrest.

The most at risk were people who did not get 7.5 hours of sleep and whose blood pressure increased overnight.

Scientists concluded that short sleep periods are a predictor of cardiovascular disease in the elderly population.

The National Institutes of Health reports that eight hours of sleep per night is the optimal amount for adults, with adolescents requiring nine or more. Additionally, according to the NIH, missing just one hour of sleep per night causes the body to accumulate a “sleep debt” which can have an effect on performance, thinking and mood.