Curtailed Sleep May Alter How Intense Exercise
Stresses the Heart
From:
Uppsala University
January 27, 2022 -- In a new study,
participants underwent an intense bout of exercise after both normal sleep and
after three nights of curtailed sleep. When they exercised after curtailed
sleep, the levels of the heart injury biomarker troponin increased slightly
more, compared with when the participants performed exercise in their
well-rested condition. The study is a smaller pilot study and it is not yet
possible to determine if the findings may be of relevance for cardiovascular
health. The study is published in the journal Molecular Metabolism.
Previous epidemiological studies have
demonstrated that, at the population level, chronically disrupted and shortened
sleep increases the risk of several cardiovascular diseases, such as high blood
pressure and myocardial infarction. In contrast, physical exercise can reduce
the risk of cardiovascular disease. However, it has been unknown whether
controlled sleep restriction can modulate cardiac stress during strenuous
exercise.
"Exercise is great for the heart,
while lack of sleep can adversely impact the cardiovascular system. But it has
been unknown whether shortened sleep can modulate the physiologic stress that
intense exercise seems to have on the cells of the heart," says Jonathan
Cedernaes, physician and associate professor of medical cell biology at Uppsala
University, who led the study.
A specific type of the protein troponin
is found in the heart's muscle cells. Low amounts of troponin can be released
after high-intensity training. Levels of troponin are routinely determined in
the clinic, as significantly higher levels are seen in the setting of acute
cardiovascular events.
"Higher blood levels of troponin
after exercise have been linked to a relative increased prospective risk of
cardiovascular diseases. It is not really known what the mechanism is, but at
the same time, we know that one's cardiovascular health is modulated through an
interplay of lifestyle factors. We therefore thought it would be important to
investigate whether the release of troponin during exercise can be affected by
sleep restriction. One reason is the fact that many occupations entail work
that disrupts sleep, such as for healthcare workers," says Cedernaes.
Previous studies have found that
exercise can counteract certain adverse effects of curtailed sleep on
metabolism. Furthermore, data at the population level indicate that exercise
can counteract the negative effects of chronic sleep loss on the cardiovascular
system.
"Those who report exercising on a
regular basis, but get less sleep than the ideal amount, still reduce their
risk of dying from cardiovascular disease. At the same time, we know that
chronic or recurrent sleep disruption is bad for cardiovascular health. It is
therefore possible that a more pronounced lack of sleep in the long run can
increase the relative risk that the heart is injured in some way by more
intense exercise. But many individuals experience a temporary lack of sleep,
and the need for sleep is also very individual," Cedernaes points out.
"The epidemiological evidence related to disturbed sleep per se, applies
primarily to chronic lack of sleep and long-term shift work, and are seen when
averaging at the population level."
16 young men, healthy and normal-weight,
underwent the study. All were extensively screened for previous cardiovascular
disease, as well as for heredity for such conditions. In addition, all
participants had normal sleeping habits within the recommended range -- that
is, they reported getting 7-9 hours of sleep on a regular basis.
The participants were monitored in a
sleep laboratory, where their meal and activity schedules were standardized. In
one of the two sessions, participants got a normal amount of sleep, three
nights in a row. During their other session, the participants were kept awake
for half the nights, three nights in a row. On each occasion, blood samples
were taken in the evening and in the morning. After both sleep interventions,
blood samples were also taken on the last day, both before and after a
30-min-long intense stationary cycling session.
The researchers measured two biomarkers
in the blood samples. NT-proBNP reflects the load on the heart. The second
protein, troponin, is commonly used as a marker of cardiac injury. The results
showed that the levels of NT-proBNP increased in response to exercise, but this
increase did not differ depending on the amount of sleep. Blood levels of
troponin also increased after the workout. However, for troponin, the increase
after exercise was almost 40% higher after three nights of partial sleep
restriction, compared with after three nights of normal sleep.
"An important observation was that
the levels of troponin and NT-proBNP were not elevated in response to sleep
restriction at any time prior to the workout. It is possible that lack of sleep
may instead lower the threshold at which an increased exercise load results in
measurable stress in heart muscle cells, as may occur in response to strenuous
exercise," says Cedernaes. "However, we noted that the increase in
circulating troponin levels following exercise was variable across individuals.
Previous research under resting conditions has also hinted at such variability,
and it would be interesting to uncover the mechanisms."
Cedernaes continues:
"Today there is no evidence to
suggest that it would be harmful to the heart if you exercise regularly when
you have slept too little. One can instead turn the argument around: by
ensuring that one gets enough sleep, one may further increase the positive
impact of physical exercise. While we know that high-intensity training
generally has benefits in the long run, our results may be worth considering
and exploring in specific groups of individuals. Examples include athletes and
the military. These groups may be required to perform at extreme physical
levels even under conditions of curtailed sleep. It may be good to further
consider the importance of sleep in these contexts, especially as we also know
that improving sleep can also improve one's performance, both cognitively and
physically."
One limitation of the current study was
that only 16 individuals were included. The study should be considered as a
pilot study that requires further validation and follow up. Such studies are
also needed to examine if these changes also apply to other age groups or
women.
https://www.sciencedaily.com/releases/2022/01/220127114315.htm
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