People who sleep for short periods of time are more at risk of chronic diseases in adult life, a study has suggested.
Sleep has long been known to be associated with overall health. The U.S. National Institutes of Health states that good sleep improves brain performance and that lack of quality sleep regularly raises the risk of many diseases and disorders, including heart disease, stroke, obesity and dementia.
However, the association between sleep duration and multimorbidity—the presence of multiple diseases or conditions—is poorly understood, researchers say.
To investigate this, researchers examined decades-old data from the landmark Whitehall II cohort study, which was a large study conducted between 1985 and 1988 to examine the health of over 10,000 people employed in the British civil service.
Followup reports on the people who took part in the study have been carried out several times in the decades since, with self-reported sleep duration measured six times between 1985 and 2016.
Using this data, researchers identified 7,864 people and extracted sleep duration reports at age 50, 60 and 70 and looked at the relationship between this and incidence of multimorbidity over the course of 25 years.
The data showed a “robust association” between people getting five or less hours’ sleep per night and a higher risk of multimorbidity. The researchers identified a 20 percent increased risk of a first chronic disease associated with short sleep duration at age 50, and a “similar increased risk of subsequent multimorbidity.”
The results did not show any associations with death, however. The data also suggested that there was an increased risk of multimorbidity with long sleep duration in older individuals, but the researchers said this might reflect the need for longer sleep in people who were already ill.
Russell Foster is professor of circadian neuroscience and head of the Department of Ophthalmology at the University of Oxford in the U.K. He told Newsweek that he thinks the new report is “cautious” and added: “These data are entirely consistent with earlier recommendations, which are that if you’re getting below six [hours of sleep] then it’s probably not healthy.”
Explaining why lack of sleep might be harmful, Foster said night shift workers are a “classic example.”
“They’re trying to sleep during the day and frequently get five hours or less. So what is going on? Well, it’s likely that a key contributing factor will be activation of the stress axis.
“Short-term stress is a bit like the first gear of a car, it gives you that wonderful acceleration to run away or fight. But if you keep the car in first gear, you’re going to destroy the engine. And that’s what’s happening, I think, with short-duration sleep. By activating the stress axis, you’re increasing blood pressure, you’re increasing heart rate, you’re throwing glucose into the circulation.
“High levels of cortisol are associated with suppressed immunity, so higher rates of infection, higher rates of cancer. So I think many of the problems we’re seeing could be associated with activation of the stress axis.”
Jim Horne, emeritus professor of sleep research at Loughborough University in the U.K. and former editor of the Journal of Sleep Research, told Newsweek: “It has been known for a long time that less sleep is linked to health conditions but not necessarily the cause.
“Although that paper might imply that over five hours might be OK. I think six is probably the minimum.”
Horne added that people can worry too much about sleep which can have the opposite effect they want, and that that amount of sleep needed varies between individuals.
“In general, people naturally vary in the sleep they need and saying that we all must have seven to eight hours and the consequences for health for not getting this can unnecessarily add to the worries of people suffering from, for example, insomnia and their ‘not getting enough sleep.’ Besides, simply judging sleep by its quantity is simplistic and overlooks the importance of its quality, which is critical.
“The acid test of sufficient sleep is the extent to which we can remain alert throughout the day until bedtime, apart from that natural ‘afternoon dip’ when a short nap—ideally keep it within 20 minutes so as not to impact too much on night sleep—can be very refreshing.”
The study was published in the journal PLOS Medicine on October 18.