In one study, participants completed an intense workout after a normal night’s sleep and after three nights of reduced sleep. When they exercised after reduced sleep, levels of the heart damage biomarker troponin rose slightly more than when participants exercised after a full night’s sleep. This study, published in the journal Molecular Metabolism, is a small pilot study.

How Reduced Sleep Affects Heart Health

Previous epidemiological studies have shown that chronic sleep disturbance and reduced sleep at the population level increase the risk of various cardiovascular diseases such as high blood pressure and heart attack. In contrast, physical exercise can reduce the risk of cardiovascular disease. However, it has long been unknown whether controlled sleep restriction can modulate cardiac stress during intense physical activity. “Exercise is good for the heart, while sleep deprivation can have a negative effect on the cardiovascular system. However, it was previously unknown whether reduced sleep can modulate the physiological stress that intense exercise appears to exert on heart cells,” said Jonathan Cedernaes, MD, PhD, associate professor of medical cell biology at Uppsala University, who led the study.

A specific type of protein called troponin is found in heart muscle cells. After high-intensity exercise, small amounts of troponin can be released. Troponin levels are routinely measured in clinics, as significantly higher levels are observed in acute cardiovascular events. “Higher troponin levels in the blood after exercise have been associated with a relatively increased prospective risk of cardiovascular disease. The mechanism behind this is not really known, but at the same time we know that cardiovascular health is influenced by the interaction of various lifestyle factors. We therefore considered it important to investigate whether the release of troponin during exercise can be influenced by sleep deprivation. One reason for this is the fact that many professions involve a workload that disrupts sleep, for example in the healthcare sector,” says Cedernaes.

Previous studies have shown that physical activity can counteract certain negative effects of sleep deprivation on metabolism. In addition, population-level data suggest that physical activity can offset the negative effects of chronic sleep deprivation on the cardiovascular system. “People who report exercising regularly but getting less than the ideal amount of sleep still reduce their risk of dying from cardiovascular disease. At the same time, we know that chronic or recurrent sleep disturbances are bad for cardiovascular health. It is therefore possible that more pronounced sleep deprivation may increase the relative risk of the heart being damaged in some way by more intense exercise in the long term. But many people suffer from temporary sleep deprivation, and sleep requirements are also very individual,” Cedernaes emphasized. “The epidemiological findings regarding sleep disorders themselves primarily apply to chronic sleep deprivation and long-term shift work and become apparent when averaging at the population level.”

The Role of Troponin

Sixteen young men, all healthy and of normal weight, participated in the study. All were thoroughly examined for previous cardiovascular disease and for the hereditary predisposition to such diseases. In addition, all participants had normal sleep habits within the recommended range—that is, they reported getting 7 to 9 hours of sleep on a regular basis. The participants were monitored in a sleep laboratory, where their meals and activities were standardized. In one of the two sessions, they enjoyed a normal amount of sleep for three nights in a row. During the other session, the participants were kept awake for half the night for three nights in a row. Blood samples were taken in the evening and morning on each occasion. After both sleep interventions, blood samples were also taken on the last day, both before and after a 30-minute intense stationary cycling session.

The researchers measured two biomarkers in the blood samples. NT-proBNP reflects the strain on the heart. The second protein, troponin, is often used as a marker for heart damage. The results showed that NT-proBNP levels increased in response to exercise, but this increase was independent of sleep duration. Blood troponin levels also increased after exercise. However, for troponin, the increase after exercise was almost 40% higher after three nights of partial sleep restriction than after three nights of normal sleep. An important observation was that troponin and NT-proBNP levels were not elevated in response to sleep restriction at any time prior to exercise. It is possible that sleep deprivation instead lowers the threshold at which increased exercise load leads to measurable stress in the heart muscle cells, as can occur in response to strenuous exercise. However, the researchers found that the increase in circulating troponin levels after exercise varied from person to person. Previous studies under resting conditions have also pointed to such variations, and it would be interesting to uncover the mechanisms involved.

Further Research Important

According to the researchers, there is currently no evidence that regular exercise is harmful to the heart, even if you have not had enough sleep. The argument can also be turned around: by ensuring sufficient sleep, the positive effects of physical exercise can be further enhanced. Although it is known that high-intensity training generally has long-term benefits, the results may be worth considering and investigating in certain groups of people. Examples include athletes and soldiers. These groups may have to perform extreme physical feats even under conditions of limited sleep. It may be worthwhile to further investigate the importance of sleep in these contexts, especially since it is known that improving sleep can also improve cognitive and physical performance. One limitation of the study was that it only included 16 people.