Poor sleep has been linked to heart disease for a while now, but new research may have revealed how exactly not getting enough sleep hurts your heart and blood vessels.

According to the Centers for Disease Control and Prevention (CDC), studies have shown that not getting enough sleep increases a person's risk for several heart problems, such as high blood pressure, heart disease, heart attacks and stroke. However, the biological reason for this connection between sleep and heart disease has remained a mystery — until now.

In a study published in the journal Nature, scientists found that proper sleep helps prevent atherosclerosis, which is a condition characterized by plaque build-ups inside the arteries, causing them to harden. On the flip side, researchers said that fragmented sleep would worsen this condition. 

Scientists reached this conclusion after conducting a study in mice that were genetically prone to atherosclerosis. They allowed some of the mice to get enough sleep, while others were frequently woken up from their slumber by a "sweep bar" that automatically moved across the bottom of their cage. 

The mice which had their sleep interrupted frequently showed no change in terms of weight or cholesterol levels compared to the ones which were allowed a sufficient amount of sleep. However, compared to the sleep-sufficient mice, the sleep-deprived subjects were found with larger plaques in their arteries and increased inflammation in their blood vessels.

From their observations, scientists found that disrupted sleep alters the levels of the hormone hypocretin, or orexin, in the brain, specifically the hypothalamus. Hypocretin is believed to promote wakefulness in humans, and it is often found in low levels for people suffering narcolepsy. Previous studies have suggested that narcolepsy has been known to increase the risk of heart disease, the new research noted.

The lower levels of hypocretin, in turn, resulted to a boost in the levels of signalling protein CSF1, which then caused accelerated atherosclerosis and increased production of inflammatory white blood cells in the bone marrow. In the study, scientists also found that bringing hypocretin levels back up reduced atherosclerosis in the mice. 

Study senior author Filip Swirski, of the Massachusetts General Hospital Center for Systems Biology, talked about their findings in a statement.

"We have discovered that sleep helps to regulate the production … of inflammatory cells and the health of blood vessels and that, conversely, sleep disruption breaks down control of inflammatory cell production, leading to more inflammation and more heart disease," Swirski said. "We also have identified how a hormone in the brain known to control wakefulness … protects against cardiovascular disease."

However, the researchers said that studies need to be conducted in humans for the findings to be considered conclusive as their tests were only done in mice. 

"We now need to study this pathway in humans," Swirski said.