Hot tub time

Taking one hot bath a day lowers the risk of 3 deadly diseases — study

Soak it off.

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Who doesn’t like taking a hot bath to soak off the stress of a long day at work? And according to a new study published this week in the journal Heart, getting clean isn’t the only thing baths are good for.

In a longitudinal study, researchers used data collected from more than 61,000 people in Japan since 1990 to show that the more you bathe, the lower your risk of dying from heart disease, heart attack, and stroke.

The findings suggest that taking one hot bath every day significantly protects your cardiovascular health, and keeps the doctor away.

Soak it off

The results fit with other research that shows why you gravitate towards a hot bath when you’re feeling a little off.

In a 2016 study, researchers found that heat therapy may protect against cardiovascular disease. The association, the authors of that study said, may be to do with the effect heat has on the body, which is similar to that of physical exercise.

Bathing is linked with a good night sleep and self care routine, and associated with better overall health. It may also benefit people with specific health conditions. For example, a 1999 study linked hot-tub therapy to improved blood pressure and weight control among people with type-2 diabetes.

But this research, which uses data collected by the Japan Public Health Center, is the largest study to examine the long-term link between tub bathing and heart health.

The Center tracked more than 61,000 adults between the ages of 45 and 59 in the five areas of Akita, Iwate, Tokyo, Nagano and Okinawa. They were monitored until December 2009, or until death in some cases.

When the study began in 1990, over 43,000 of those individuals completed a questionnaire about their showering and bathing habits, and their lifestyle, answering questions about their medical history, education, diet, smoking, and exercise.

They also answered questions such as "How often do you bathe in a tub in 1 week?"

During this time there were:

  • 2097 cases of cardiovascular disease
  • 275 heart attacks
  • 53 sudden cardiac deaths
  • 1769 strokes

The researchers then calculated how bathing habits correlated with heart health for each study participant.

In Japan, most people bathe standing up, completely immersed in water heated to about 40-42 degrees Celsius.

Among those taking part in the study, people who bathed once a day had 28 percent lower risk of cardiovascular disease overall, and a 26 percent lower risk of stroke, compared to those who only bathed once or twice a week, or never at all.

Interestingly, the frequency of bathing wasn't the only thing that mattered to improved health outcomes. The temperature of the water made a significant difference, too.

Individuals who preferred warmer water had 26 percent lower risk of overall cardiovascular disease, but those who liked it hot had 35 percent lower risk. The same was not true for strokes, however.

Cumulative Kaplan-Meier curve for proportion of free from cardiovascular disease according to the frequency of tub bathing per week.From the study, journal Heart.

"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," the researchers report.

The study suggests that clinicians can recommend tub bathing to protect against cardiovascular disease.

Not all hot baths are equal

“If confirmed the findings are fantastic. Reducing cardiovascular disease deaths by such a simple technique,” Andrew Felix Burden, a cardiology and diabetes expert, tells Inverse. Burden was not involved in the new study, but did write an editorial in the journal Heart to accompany it.

Ultimately, the results may offer a non-pharmaceutical solution to cardiovascular problems, he says.

But while these findings are promising, there are other factors to keep in mind.

“The study is observational," Burden explains.

"It is therefore not proven, but hypothesis setting. Further randomized trials are needed to confirm it, then further work to find out why."

"And if you are young, then yes you should bathe daily."

That means that while the study points to a link between bathing habits and heart health, it cannot prove that a bath a day definitively protects against heart disease. And the study focuses on Japan, where people have specific bathing practices that might not translate to other cultures.

The study has other limitations, too. The researchers did not track how participants' bathing habits changed over time, so they are based on data from one time point, only, for example.

The study also did not find a link between taking hot baths and lowering risk of sudden cardiac deaths. In fact, the researchers point out that, especially among an older population, hot baths may be associated with sudden deaths, including higher incidence of accidental drowning and heat stroke.

It is also not known if cold water could confer similar or different health benefits, Burden says.

He hopes there will be further investigation to establish the role temperature may play, if any, in these preliminary results.

As of now, these results are promising enough that Burden recommends younger people bathe daily if they want to see any positive heart health effects. It is also just good hygiene, and no matter who you are, we can all stand to gain from keeping ourselves clean.

Longevity Hacks is a regular series from Inverse on the science-backed strategies to live better, healthier, and longer without medicine.

HOW THIS AFFECTS LONGEVITY — This study tracked more than 61,000 Japanese adults from 1990 until 2009. Overall, they found that people who took a bath once a day had a 28 percent lower risk of cardiovascular disease and a 26 percent lower risk of stroke, compared to those who never bathed or only bathed once or twice a week.

WHY IT’S A HACK — Frequency of bathing as associated with improved health outcomes, as was the temperature of the bath. Warm water was associated with a 26 percent lower risk of all cardiovascular disease, but people who liked especially hot baths had a 35 percent lower risk. This jibes with previous research that claims heat therapy can protect against cardiovascular disease.

SCIENCE IN ACTION — Importantly, this is an observational study — it can’t prove why hot baths are linked to these positive results. But outside commenter, and cardiology expert, Andrew Felix Burden tells Inverse that if confirmed the “findings are fantastic” especially because they are linked to such a simple technique.

HACK SCORE OUT OF 10 — 🛀🛀🛀🛀🛀 (5/10 hopeful bathers)

Abstract: Tub bathing is considered to have a preventive effect against cardiovascular disease (CVD) by improving hemodynamic function. However, no prospective studies have investigated the long-term effects of tub bathing with regard to CVD risk. A total of 30 076 participants aged 40–59 years with no history of CVD or cancer were followed up from 1990 to 2009. Participants were classified by bathing frequency: zero to two times/week, three to four times/week and almost every day. The HRs of incident CVD were estimated using Cox proportional hazards models after adjusting for traditional CVD risk factors and selected dietary factors. During 538 373 person-years of follow-up, we documented a total of 2097 incident cases of CVD, comprising 328 coronary heart diseases (CHDs) (275 myocardial infarctions and 53 sudden cardiac deaths) and 1769 strokes (991 cerebral infarctions, 510 intracerebral hemorrhages, 255 subarachnoid hemorrhages, and 13 unclassified strokes). The multivariable HRs (95% CIs) for almost daily or every day versus zero to two times/week were 0.72 (0.62 to 0.84, trend p<0.001) for total CVD; 0.65 (0.45 to 0.94, trend p=0.065) for CHD; 0.74 (0.62 to 0.87, trend p=0.005) for total stroke; 0.77 (0.62 to 0.97, trend p=0.467) for cerebral infarction; and 0.54 (0.40 to 0.73, trend p<0.001) for intracerebral haemorrhage. No associations were observed between tub bathing frequency and risk of sudden cardiac death or subarachnoid hemorrhage. The frequency of tub bathing was inversely associated with the risk of CVD among middle-aged Japanese.
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