For the first time, a study has shown a clear link between the frequency and
duration of unconscious wakefulness during night-time sleep and an increased
risk of dying from diseases of the heart and blood vessels, and death from
any cause, particularly in women.
The study of 8001 men and women, which is published today (Tuesday) in the
European Heart Journal [1], found that women who experienced unconscious
wakefulness most often and for longer periods of time had nearly double the
risk of dying from cardiovascular disease during an average of between 6 and
11 years’ follow-up, when compared to the risk in general female population.
The association was less clear in men, and their risk of cardiovascular
death increased by just over a quarter compared to the general male
population.
Unconscious wakefulness, also known as cortical arousal, is a normal part of
sleep. It occurs spontaneously and is part of the body’s ability to respond
to potentially dangerous situations, such as noise or breathing becoming
obstructed. Pain, limb movements, trauma, temperature and light can also be
triggers.
Dominik Linz, associate professor in the cardiology department at Maastricht
University Medical Center (The Netherlands), explained: “A common trigger
for nocturnal arousals is obstructive sleep apnoea when breathing stops and
the arousal system ensures the activation of our body to change our sleep
position and to reopen the upper airway. Another cause of arousals can be
‘noise pollution’ during the night by, for example, night-time aircraft
noise. Depending on the strength of the arousal, a person might become
consciously aware of the environment, but often that is not the case.
Typically, people will feel exhausted and tired in the morning because of
their sleep fragmentation but will not be aware of the individual arousals.”
Previous research has shown that sleep duration, either too short or too
long, is associated with increased risks of death from cardiovascular or
other causes. However, until now, it was unknown whether there was also a
link with the arousal burden (a combination of the number of arousals and
their duration) during a night’s sleep and the risk of death.
In a collaboration between a team led by associate professor Mathias Baumert
from the School of Electrical and Electronic Engineering at the University
of Adelaide (Australia) and Prof. Linz, researchers looked at data from
sleep monitors worn overnight by men and women taking part in one of three
studies: 2782 men in the Osteoporotic Fractures in Men Sleep Study (MrOS),
424 women in the Study of Osteoporotic Fractures (SOF), and 2221 men and
2574 women in the Sleep Heart Health Study (SHHS). The average ages in the
studies were 77, 83 or 64 years, respectively. The participants were
followed up over a period of several years, which ranged from an average of
six years (SOF) to 11 years (MrOS).
After adjusting for factors that could affect the results such as total
sleep duration, age, medical history, body mass index (BMI) and smoking
habits, the researchers found that women had an arousal burden that was
lower than men. However, those who had an arousal burden that accounted for
more than 6.5% of their night’s sleep had a greater risk of dying from
cardiovascular disease than women with a lower arousal burden: double the
risk in SOF and 1.6 times the risk in SHHS. Their risk of dying from all
causes was also increased by 1.6 times in SOF and 1.2 times in SHHS.
Taking the women from both studies together, those with an arousal burden of
more than 6.5% had a 12.8% risk of dying from cardiovascular disease, nearly
double that of women of a similar age in the general population who had a
risk of 6.7%. The risk of dying from any cause was 21% among women in the
general population, which increased to 31.5% among women in the two studies
with an arousal burden of more than 6.5%
Men with an arousal burden accounting for more than 8.5% of their night’s
sleep had 1.3 times greater risk of dying from cardiovascular disease (MrOS)
or any cause (SHHS), compared to men with lower arousal burdens, but
findings for increased risk of death from any cause in MrOS or
cardiovascular disease in SHHS were not statistically significant.
When the researchers looked at all the men in both studies, those with an
arousal burden of more than 8.5% had a risk of 13.4% and 33.7% of dying from
cardiovascular disease or any cause, respectively, compared to the risk in
the general population of men of similar ages of 9.6% and 28%, respectively.
Prof. Linz said: “It is unclear why there is a difference between men and
women in the associations, but there are some potential explanations. The
triggers causing an arousal or the body’s response to arousal may differ in
women compared to men. This may explain the relatively higher risk of
cardiovascular death in women. Women and men may have different compensatory
mechanisms for coping with the detrimental effects of arousal. Women may
have a higher arousal threshold and so this may result in a higher trigger
burden in women compared to men.”
He said that older age, BMI and the severity of sleep apnoea increase
arousal burdens. “While age cannot be changed, BMI and sleep apnoea can be
modified and may represent an interesting target to reduce arousal burdens.
Whether this will translate into lower risks of dying from cardiovascular
disease warrants further study. For me as a physician, a high arousal burden
helps to identify patients who may be at higher risk of cardiovascular
disease. We need to advise our patients to take care of their sleep and
practice good sleep ‘hygiene’. Measures to minimise noise pollution during
the night, lose weight and treat sleep apnoea could also help to reduce the
arousal burden.”
Prof. Baumert said: “In order to include assessment of arousal burdens into
routine strategies for reducing the risk of cardiovascular disease, we need
easily scalable, widely accessible and affordable techniques to estimate the
duration and fragmentation of sleep and to detect arousals. Wearable devices
for measuring activity and changes in breathing patterns may provide
important information.”
Limitations of the study include that it was conducted in older, mainly
white people and so its findings cannot be extrapolated to other races or
younger men and women. The researchers did not consider the possible effect
of medications; monitoring of the participants’ sleep was conducted on a
single night and so does not take account of night-to-night variations.
Finally, it can only show there is an association between greater sleep
arousal burden and increased risk of death, not that sleep arousals cause
the increased risk.
In an accompanying editorial [2], Professor Borja Ibáñez, clinical research
director at the Centro Nacional de Investigaciones Cardiovasculares Carlos
III, Madrid (Spain), and colleagues, who were not involved in the research,
write that a strength of the study is that the arousal burden was measured
objectively with sleep monitors, rather than being self-reported by the
participants. They point out that disruption of the body’s natural circadian
rhythm is known to be involved in the development of often undetected fat
accumulation in arteries and this could be a possible mechanism for the
increase in the risk of cardiovascular problems.
They continue: “Even though many knowledge gaps on the relationship between
sleep and CVD [cardiovascular disease] remain to be studied in the coming
years, this study provides solid evidence supporting the importance of sleep
quality for a better CV health. Further evidence combining comprehensive
sleep evaluation with biological sampling and long-term follow-ups will be
desirable . . . What remains to be determined is whether an intervention
aiming at improving sleep quality is able to reduce the incidence of CV
events and mortality. While awaiting these trials, we wish you sweet
dreams.”
References:
Sobhan Salari Shahrbabaki, Dominik Linz, Simon Hartmann, Susan Redline,
Mathias Baumert. Sleep arousal burden is associated with long-term all-cause
and cardiovascular mortality in 8001 community-dwelling older men and women.
European Heart Journal, 2021; DOI:
10.1093/eurheartj/ehab151
Inés García-Lunar, Valentín Fuster, Borja Ibanez. Good night, sleep tight.
European Heart Journal, 2021; DOI:
10.1093/eurheartj/ehab181
Tags:
Biology & Health