Both people who sleep very little and those who
sleep a lot have increased cardiovascular risk. A
new study of nearly 400,000 people shows that
getting enough sleep may be especially important for
women and the elderly.
Sleeping less than four hours or more than eight
hours a night increases the risk of dying from some
types of coronary heart disease, such as heart
attacks and unstable angina pectoris, according to a
study by Norwegian and Taiwanese researchers.
“This is the single largest study that has looked at
how sleep duration affects the risk of dying from
cardiovascular disease. Our results show that
enough, but not too much sleep is important for a
healthy lifestyle,” says first author and
postdoctoral fellow Linn Beate Strand at the NTNU’s
Department of Public Health and General Practice.
Doctors asked 392,164 adults who came for a health
check in Taiwan between 1998 and 2011 how long they
usually slept at night. Of those, 711 of the
participants died of cardiovascular disease during
the follow-up period. It turned out that the risk
increased 50 per cent for participants who slept
fewer than four hours compared with participants who
slept between six and eight hours.
Part of the difference might be explained by the
fact that participants who slept the least had a
less favourable risk profile for cardiovascular
disease, but even after adjusting for these factors,
the risk of heart-related death increased by 36 per
cent.
According to Strand, exactly how too little sleep
affects the risk of dying from cardiovascular
disease is still uncertain, but a number of theories
have been proposed to explain the phenomenon. Less
sleep is associated with stress responses that
increase heart rate, blood pressure and secretion of
adrenaline, for example, all of which are known risk
factors for cardiovascular disease. Sleep
deprivation has also been associated with the
secretion of inflammatory substances, and previous
studies have shown an association between short
sleep duration, decreased insulin sensitivity,
obesity and diabetes.
Participants who reported that they slept more than
eight hours a night also had a 53 per cent increased
risk of dying from coronary heart disease compared
with participants who slept between six and eight
hours. After adjusting for other risk factors, the
risk was still 28 per cent higher.
“We don’t know the mechanisms that could explain a
direct causal link between long sleep duration and
an increased risk of dying from coronary heart
disease,” Strand says.
Education and marital status were among the
variables that the researchers adjusted their
analyses for, in addition to well-known risk factors
such as age, sex, BMI, systolic blood pressure,
blood glucose, blood lipids, smoking, alcohol use,
physical activity level and previous cardiovascular
disease or diabetes. The increased risk could not be
explained by the use of sleep medications.
Nevertheless, part of the explanation could lie in
factors that researchers lacked information on and
that could potentially be associated with both
increased cardiovascular risk and prolonged sleep,
such as unemployment, low socioeconomic status,
depression and sleep apnoea.
No increased risk was associated with sleeping
between four and six hours a night as compared to
sleeping between six and eight hours.
Furthermore, researchers found that the increased
risks of both short and long sleep duration
primarily affected women. The relationship between
sleep duration and the risk of dying from
cardiovascular disease was also slightly stronger in
the 65 years and older population than in younger
individuals.
“Women are more prone to sleep problems than men,
and also previous studies have shown that women who
sleep a little or a lot may be at increased risk for
cardiovascular disease,” says Strand. She emphasizes
that the findings should be interpreted with caution
and do not necessarily mean that short or long sleep
duration is more dangerous for women than for men.
For more information
Linn B. Strand, Min Kuang Tsai, David Gunnell, Imre
Janszky, Chi Pang Wen, Shu-Sen Chang. Self-reported
sleep duration and coronary heart disease mortality:
A large cohort study of 400,000 Taiwanese adults.
International Journal of Cardiology, Volume 207, 15
March 2016, p. 246–251
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