Regular tub bathing is linked to a
lower risk of death from heart disease and stroke, indicates a long term study,
published online in the journal Heart.
And the higher
the ‘dose,’ the better it seems to be for cardiovascular health, with a daily
hot bath seemingly more protective than a once or twice weekly one, the
findings indicate.
A linked
editorial sounds a note of caution, however, because sudden death associated
with hot baths is relatively common in Japan, where the study was conducted.
Having a bath is
associated with good sleep quality and better self-rated health, but it’s not
clear what its long term impact might be on cardiovascular disease risk,
including heart attack, sudden cardiac death, and stroke.
To explore this
further, the researchers drew on participants in The Japan Public Health Center
based Study Cohort 1, a population based tracking study of more than 61,000
middle aged adults (45 to 59 years).
At the start of
the study in 1990, some 43,000 participants completed a detailed questionnaire
on their bathing habits and potentially influential factors: lifestyle, to
include exercise, diet, alcohol intake, weight (BMI); average sleep duration;
and medical history and current medicines use.
Each participant
was monitored until death or completion of the study at the end of December
2009, whichever came first, with the final analysis based on 30,076 people.
During the
monitoring period, 2097 cases of cardiovascular disease occurred: 275 heart
attacks; 53 sudden cardiac deaths; and 1769 strokes.
After taking
account of potentially influential factors, analysis of the data showed that
compared with a once or twice weekly bath or no bath at all, a daily hot bath
was associated with a 28% lower overall risk of cardiovascular disease, and a
26% lower overall risk of stroke.
The frequency of
tub bathing wasn’t associated with a heightened risk of sudden cardiac death,
or with a particular type of stroke, called subarachnoid haemorrhage (bleed
into the space surrounding the brain).
Further analysis
of preferred water temperature indicated 26% lower and 35% lower risks of
overall cardiovascular disease for warm and hot water, respectively. But no
significant associations emerged for overall stroke risk and water temperature.
After excluding
those participants who developed cardiovascular disease within 5 or 10 years of
the start of the study, the associations found weren’t quite as strong, but
nevertheless still remained statistically significant.
This is an
observational study, and as such, can’t establish cause, added to which changes
in bathing frequency weren’t tracked during the monitoring period. The typical
style of Japanese bathing also includes immersion to shoulder height, and this
may be a critical factor.
But, say the
researchers, previously published research has pointed to a link between heat
exposure and cardiovascular disease prevention: this is because the effects of
heat on the body are not dissimilar to those of exercise.
“We found that
frequent tub bathing was significantly associated with a lower risk of
hypertension, suggesting that a beneficial effect of tub bathing on risk of
[cardiovascular disease] may in part be due to a reduced risk of developing
hypertension,” write the researchers.
They acknowledge
that taking a hot bath is not without its risk, particularly if the temperature
is too high, a point that is taken up by Dr Andrew Felix Burden in a linked
editorial.
“There can be no
doubt about the potential dangers of bathing in hot water, and the occurrence
of death from this increases with age, as well as with the temperature of the
water,” he writes.
Although
cardiovascular disease itself is unlikely to be the cause of these deaths,
overheating, leading to confusion and drowning, most likely is, he suggests.
“Investigations
into the potential cardiovascular benefit of heat-free immersion in warm to hot
water are needed,” he says. “In the meanwhile, caution is needed because of the
higher mortality associated with such bathing in an unselected population.”
Journal article: https://heart.bmj.com/content/early/2020/03/03/heartjnl-2019-316187
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