“For people with busy lives, sleeping may feel like a waste of time, but our study suggests that short sleep could be linked with future cardiovascular disease,” said Moa Bengtsson of the University of Gothenburg, Sweden.
Previous studies have generated conflicting evidence on whether short sleep is associated with a greater chance of having a future cardiovascular event. This study investigated this relationship in 50-year-old men.
In 1993, 50% of all men born in 1943 and living in Gothenburg were randomly selected to participate in the study. Of the 1,463 invited, 798 (55%) men agreed to take part. Participants underwent a physical examination and completed a questionnaire on current health conditions, average sleep duration, physical activity, and smoking. The men were divided into four groups according to their self-estimated average sleep duration at the start of the study: five or fewer hours, six hours, seven to eight hours (considered normal sleep duration), and more than eight hours.
Participants were followed up for 21 years for the occurrence of major cardiovascular events, which included heart attack, stroke, hospitalization due to heart failure, coronary revascularization, or death from cardiovascular disease. Data on cardiovascular events were collected from medical records, the Swedish Hospital Discharge Registry, and the Swedish Cause of Death Register.
Men with incomplete data on sleep duration, incomplete follow-up information, or who had a major cardiovascular event before the start of the study were excluded, leaving a total of 759 men for the analyses.
High blood pressure, diabetes, obesity, current smoking, low physical activity, and poor sleep quality were more common in men who slept for five or fewer hours per night, compared with those who slept for seven to eight hours.
Compared with those with normal sleep duration, men who slept for five or fewer hours per night had a twofold higher risk of having a major cardiovascular event by age 71. The risk remained doubled after adjusting for cardiovascular risk factors at the start of the study, including obesity, diabetes, and smoking.
“Men with the shortest sleep duration at the age of 50 were twice as likely to have had a cardiovascular event by age 71 as those who slept a normal amount, even when other risk factors were taken into account,” said Ms. Bengtsson.
“In our study, the magnitude of increased cardiovascular risk associated with insufficient sleep is similar to that of smoking or having diabetes at age 50. This was an observational study, so, based on our findings, we cannot conclude that short sleep causes cardiovascular disease or say definitively that sleeping more will reduce risk. However, the findings do suggest that sleep is important, and that should be a wake-up call to all of us.”
How Long Is a Good Night’s Sleep?
Researchers have found that a sweet spot of six to eight hours’ sleep per night is most beneficial for heart health. More or less sleep is detrimental.
“We spend one-third of our lives sleeping, yet we know little about the impact of this biologic need on the cardiovascular system,” said Epameinondas Fountas, MD, of the Onassis Cardiac Surgery Centre in Athens.
The study investigated the relationship between sleep duration and cardiovascular disease using a meta-analysis that included 11 prospective studies published within the past five years of more than one million adults without cardiovascular disease.
Two groups, one with short (ie, fewer than six hours) and another with long (ie, more than eight hours) nightly sleep duration, were compared with the reference group (ie, six to eight hours’ sleep).
Short and long sleepers had a greater risk of developing or dying from coronary artery disease or stroke. Compared with adults who slept for six to eight hours per night, short and long sleepers had 11% and 33% greater risks, respectively, of developing or dying from coronary artery disease or stroke during an average follow-up of 9.3 years.
“Our findings suggest that too much or too little sleep may be bad for the heart,” said Dr. Fountas. “More research is needed to clarify exactly why, but we do know that sleep influences biologic processes like glucose metabolism, blood pressure, and inflammation, all of which have an impact on cardiovascular disease.”
A strength of the current analysis is that only prospective studies were included, noted Dr. Fountas. This technique avoids recall bias.
“Having the odd short night or lie-in is unlikely to be detrimental to health, but evidence is accumulating that prolonged nightly sleep deprivation or excessive sleeping should be avoided,” said Dr. Fountas. “The good news is that there are plenty of ways to get into the habit of getting six to eight hours a night: for example, by going to bed and getting up at the same time every day, avoiding alcohol and caffeine before bed, eating healthily, and being physically active. Getting the right amount of sleep is an important part of a healthy lifestyle.”