A new observational study has found a statistically significant link between having hot baths on a regular basis and a lower risk of cardiovascular disease and events such as stroke.
Cardiovascular disease is an umbrella term referring to various conditions that affect the heart and the vascular system.
These conditions are very common among the aging population — and according to the World Health Organization (WHO), cardiovascular disease is the top cause of death at a global level.
Certain lifestyle factors can influence a person’s risk of cardiovascular problems, and a person can take steps to change them. Among these modifiable factors are levels of exercise and the diet.
Now, new research conducted by investigators from seven Japanese institutions plus Minia University, in Egypt, has found an association between regular, frequent hot bathing and a lower risk of cardiovascular disease.
While the study was observational, and thus cannot verify that any relationship is causal, the authors suggest the possibility of a credible underlying mechanism.
“Heat exposure increases core body temperature, cardiac contractility, heart rate and blood flow, and decreases vessel endothelial shear stress,” the authors note in their study paper, published in the journal Heart.
The paper’s first author is Tomohiko Ukai, from the Osaka Prefectural Institute of Public Health and Osaka University Graduate School of Medicine, in Japan.
“These effects,” the researchers explain, “are similar to the impact of exercise and are believed to improve vascular function over the long term.”
In their study, the researchers accessed data from the Japan Public Health Center-based Study Cohort I, which included over 61,000 participants aged 45–59.
Around 43,000 of these participants filled in targeted questionnaires at the start of the study, in 1990.
Through these questionnaires, they reported information not just related to their bathing practices, but also to potential confounding factors, including exercise habits, dietary habits, alcohol intake, body mass index, average sleep duration, and medical history.
The original study included follow-up information about the participants’ health, either until their death or until the end of the study, in December 2009, whichever came first.
Finally, the researchers were able to access complete data from 30,076 individuals, which they included in their final analysis.
Between 1990 and 2009, the team recorded 2,097 deaths due to cardiovascular problems, of which 275 were related to heart attacks, 53 were related to sudden cardiac death, and 1,769 were related to stroke.
The researchers’ analysis indicated that people who had a hot bath on a daily basis had a 28% lower overall risk of cardiovascular disease and a 26% lower overall risk of stroke, compared with those who bathed twice a week or less frequently.
This analysis accounted for potentially confounding factors.
At the same time, the researchers noted that there were no associations between a person’s bathing habits and the risk of sudden cardiac death or a form of stroke known as a subarachnoid hemorrhage.
Taking their study further, the researchers found that people who preferred bathing in warm water had a 26% lower overall risk of cardiovascular disease, while those who preferred hot baths had a 35% lower risk of the same, compared with other participants.
There were no significant associations between bathwater temperature and overall stroke risk.
Finally, the researchers assessed their data again, after discounting participants who had developed cardiovascular disease within 5–10 years of the study’s start.
This analysis revealed that the associations between bathing practices and cardiovascular disease risk remained statistically significant, if not as strong as in the initial analysis.
In their study paper, the investigators caution that their research was unable to take into account certain factors, such as potential changes in bathing frequency.
They also note that they did not account for bathing styles, which can differ among people and cultures. In Japan, the country from which the study cohort hailed, the bathing style often involves immersion up to the shoulders, and the researchers suggest that this might have an impact on the effects.
Moreover, the investigators caution that the positive association between hot baths and lower cardiovascular disease risk should not discount the fact that hot baths come with their own set of health risks.
In an accompanying editorial, Dr. Andrew Felix Burden also makes this point, saying that “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.”
Bathing in water that is too hot, he notes, can lead to states of confusion, which, in turn, may lead to drowning.
Dr. Burden encourages researchers to conduct further studies about the links between hot bathing and cardiovascular health, while also urging people not to jump to conclusions based on the current study’s findings.
“Investigations into the potential cardiovascular benefit of head-free immersion in warm-to-hot water are needed. In the meanwhile, caution is needed because of the higher mortality associated with such bathing in an unselected population.”
– Dr. Andrew Felix Burden