Hot Bath on Cold Day May Harm Heart

Taking a hot bath on a cold day could spell trouble for the heart, a Japanese study hints.

Researchers found the rate of cardiac arrests during bathing rose 10-fold from summer to winter, although it was still very low overall, at 54 events per 10 million people bathing for an hour.

During cardiac arrest the heart stops beating, with fatal consequences in the majority of cases. Some 50,000 cardiac arrests occur in Japan every year, compared to 300,000 in the United States.

And new findings may be extra important in Japan, according to the new report, which is published in the journal Resuscitation.

"In Japan, most people take a deep hot bath, since traditional Japanese homes are not well-insulated as in the west, and central heating is quite uncommon," Chika Nishiyama, of Kyoto Prefectural University of Medicine School of Nursing, and colleagues write.

The researchers tapped into data from nearly 11,000 cardiac arrests occurring in Osaka Prefecture between 2005 and 2007.

Before their heart stopped, 22 percent of people had been sleeping, 9 percent had been bathing, 3 percent had been working and one-half percent had been exercising. The rest had been doing "non-specific" or unknown activities.

When looking at the cardiac arrest rates per hour of each activity, bathing was at the top of the list at 54 arrests per 10 million people, followed by 10 per 10 million people exercising.

For bathers, the risk was tied to outside temperatures, with more cardiac arrests on colder days.

While it's still unclear how to explain the link, jumping into the hot tub on a frigid day causes a rapid blood pressure drop, which stresses the heart.

As a consequence, the researchers say, "preventive approaches such as warming a bathroom and a hallway or refraining from taking a deep hot bath could be important for high-risk people."