A good night's sleep can cut heart disease risks
Short nights let harmful plaques build up in blood vessels, study finds
Sleeping at least seven hours every night can reduce the risk of a heart attack or stroke, a new study finds.
Research conducted on mice showed that rodents who didn't get enough shut-eye were more likely to develop atherosclerosis, a disease in which plaque builds up on the inner walls of the arteries.
Previous studies have found that a lack of sleep increases the risk of cardiovascular disease, but researchers haven't been able to explain how.
The team, from Massachusetts General Hospital in Boston, says its study is the first to show that a region of the brain involved in sleep is linked to bone marrow and can raise the production of white blood cells known to cause atherosclerosis.
The National Sleep Foundation recommends that adults get between 7-9 hours of sleep a night. However, a 2015 study from the Centers for Disease Control and Prevention found that about 50 percent of US adults sleep fewer than the recommended hours.
Insufficient sleep has been shown to raise the risk of obesity, diabetes, heart disease and even cancer - but researchers don't know much about the underlying mechanisms that cause this.
'We started with the premise that we know sleep is good for your heart, good for cardiovascular health, and sleep disruption is bad for your health and we’ve known this for a long time,' senior author Dr Filip Swirski, an associate professor at Massachusetts General and Harvard Medical School said.
'Our question was: "How?" We wanted to explore this known risk factor with the aim of potentially identifying tissue, cellular or molecular pathways that can explain this connection.'
For the study, published in Nature, the team genetically programmed lab mice to develop the arterial disease.
One group of mice was allowed to sleep uninterrupted for at least seven hours and the other group was repeatedly interrupted, similarly to someone one who would constantly wake up due to noise. Neither group had changes in weight or cholesterol levels.
However, the sleep-deprived mice did have more arterial plaques in their blood vessels than the mice who were allowed to sleep normally.
The mice who had interrupted sleep also had higher levels of two white blood cells, monocytes and neutrophils, that play a role in atherosclerosis.
The researchers found that hypocretin, a hormone produced in the hypothalamus region of the brain - which promotes wakefulness and appetite - controlled the production of white blood cells in bone marrow. Levels are normally high when animals are awake, but they were very low in the sleep-curtailed mice.
The drop in the hormone led to high levels of monocytes and neutrophils, in turn leading to atherosclerosis.
'The identification of a link between...the region of the brain that promotes wakefulness, appetite and how it directly communicates with bone marrow was a surprise,' said Dr Swirski.
Dr Swirski said he hopes to study this pathway in humans and see if it has implications beyond sleep in future research.
'We know cells in the bone marrow fight off infection and are linked to cancer and cardiovascular disease. We have more questions that we need answered,' he said.
He added that a cultural shift needs to take place so that adults realise how important sleep is. 'We're not - excuse the pun - waking up to the benefits of high-quality sleep,' Dr Swirski said.