Getting less than 7.5 hours of sleep per night increases the risk of stroke, heart attack and sudden death among patients with high blood pressure, a new study suggests.

In a study of more than 1,200 Japanese patients, researchers found that subjects who slept less than 7.5 hours and whose blood pressure rose when they fell asleep were four times more likely to have a stroke, fatal or non-fatal heart attack or to die suddenly.

Subjects who either slept less than 7.5 hours or had elevated blood pressure after falling asleep had between a 20 and 30 per cent increased risk of heart disease.

The findings suggest that "physicians should inquire about sleep duration in the risk assessment of patients with (high blood pressure)," the authors concluded.

The study was conducted by researchers at Jichi Medical University in Japan, Columbia University Medical Center in New York City and Stony Brook University in Stony Brook, N.Y.

The findings are published in the Archives of Internal Medicine.

The researchers followed their subjects for an average of 50 months and compiled data on how long they slept, their day and night time blood pressure and their cardiovascular history.

Doctors have long known that sleep deprivation can lead to a number of health problems, including heart disease, high blood pressure, diabetes and obesity.

However, subjects who slept less but did not experience a spike in overnight blood pressure did not have higher heart disease rates compared to those who slept longer and did not experience an overnight blood pressure increase.