Heart attack risk higher in those who sleep too little, too much
In a recent Journal of the American College of Cardiology paper, scientists from the United States and the United Kingdom describe how they analyzed sleep habits and medical records of 461,347 people aged 40–69 years living in the U.K. The data, which came from the UK Biobank, included self-reports of how many hours participants habitually slept per night and health records covering 7 years. It also included the results of tests for risk genes.
The analysis revealed that those who slept less than six hours per night had a 20 per cent higher risk of a first heart attack in comparison to those who slept six-nine hours. Those who slept more than nine hours had a 34 per cent higher risk.
The researchers also found that keeping sleep duration to six-nine hours per night can reduce the risk of a first heart attack by 18 per cent in those people with a “high genetic liability” for developing heart disease.
“This [study],” said senior study author Celine Vetter, Ph.D., an assistant professor of integrative physiology at the University of Colorado at Boulder, “provides some of the strongest proof yet that sleep duration is a key factor when it comes to heart health — and this holds true for everyone.”
Studies have been finding links between sleep habits and heart health for some time now. However, most of those findings have come from observational studies: these studies can only confirm links but cannot establish the direction of cause and effect.
Because many factors affect both sleep and heart health, it is not easy to determine whether poor sleep makes for poor heart health or poor heart health leads to poor sleep.
People who keep to the same bedtime and waking time are less likely to develop obesity, high blood pressure, and high cholesterol, study finds.
Vetter and her colleagues sought to meet this challenge by using data from a vast number of individuals, combining it with genetic research, and ruling out dozens of potential influencing factors.
Altogether, they adjusted the results to remove the potential effect of 30 factors that can influence both heart health and sleep. These factors include physical activity, mental health, income, education, smoking, and body composition.
The researchers’ results showed that sleep duration was an independent risk factor for heart attack.
The researchers found that the risk of heart attack increased the further that people’s habitual night sleep diverged from six-nine hours.
Individuals who slept five hours each night, for example, had a 52 per cent higher risk of a first heart attack than those who slept seven-eight hours. Individuals who slept 10 hours per night had double the risk.
The team then used a method called Mendelian randomization (MR) to confirm that short sleep duration was an independent risk factor for heart attack.
The MR analysis showed that individuals with gene variants that predisposed them to short sleep had a higher risk of a heart attack.
Previous studies have uncovered more than 24 variants associated with short sleep duration. By using genetic variants, MR can determine whether an observational link between a risk factor and a disease is consistent with a causal effect.
“This gives us even more confidence that there is a causal relationship here – that it is sleep duration, not something else, influencing heart health,” Vetter argued.
The latest research team hopes that its findings will raise awareness among doctors, the public, and policymakers about the impact of sleep on heart health.
“It’s kind of a hopeful message,” said first study author Iyas Daghlas, who is studying medicine at Harvard Medical School in Boston, MA, “that regardless of what your inherited risk for heart attack is, sleeping a healthy amount may cut that risk just like eating a healthful diet, not smoking, and other lifestyle approaches can.”
“Just as working out and eating healthfully can reduce your risk of heart disease, sleep can too.”