It helps to soak up the heat

Researchers agree that the health benefits of a comforting, warm bath go well beyond hygiene.

It’s a healthy sign if you prefer a regular hot bath to a daily shower.

Given the choice of a bath or a shower, my overwhelming preference is to spend time in a tub. I am, it must be said, something of a serial soaker, luxuriating in a warm, scented bath at least five times a week.

Showers are a perfunctory morning habit, but a bath is an excuse to cocoon myself away from the mayhem of family life without having to wash my hair. I am in the minority, though.

A survey of Britain’s bathing habits in 2016 revealed that a third of people bathe less frequently than once a week, and one in five admit to never taking a bath. Women are the more enthusiastic bathers, with the survey showing that 35 per cent take a regular soak compared with 29 per cent of men.

Overall, though, bathing habits are declining. And it’s a trend that could have an impact on our health.

A new study, published online in the Journal of Applied Physiologythis month, is the latest research to suggest that a regular hot bath could produce responses that mimic some of the effects of a gym workout.

In the trial, led by Christof Leicht, a physiology researcher in the school of sport exercise and health sciences at Loughborough University, a group of overweight men who did little exercise were asked to take daily hot baths in which they were submerged to their necks for an hour, or to sit in a warm room for the same amount of time.

Leicht and his team kept careful tabs on the men, recording measurements of their heart rate, blood pressure and body temperature every 15 minutes. They took samples immediately after each bathing session and two hours later. “What we found was remarkable,” Leicht says. “After two weeks there were improvements in resting blood sugar levels, important in warding off diabetes, and in the inflammatory responses that have a bearing on cardiovascular and other diseases.”

A single bath triggered some positive physiological changes, but it was regular bathing that had significant and longer-lasting effects.

An hour is a long time to soak in such heat — I tried it and was not only redder of face and body than usual, but more flustered — and there are more practical alternatives. Another recent study showed that five weekly baths lasting just 12.4 minutes brought about a health boost. Leicht says three 20-minute immersions a week also could do the trick.

“We are only beginning to understand the importance of bathing as a health measure,” he says. “There are so many reasons to make it a habit.”

Bathe for your heart

In June, a team of scientists led by Katsuhiko Kohara, a researcher in the faculty of collaborative regional innovation at Ehime University in Japan, recruited 873 study participants aged between 60 and 76 to question them about their bathing habits. His findings, published in the journal Scientific, showed that people who took at least five hot baths a week, each lasting 12.4 minutes on average, had significantly lower markers of heart disease, including atherosclerosis (the build-up of plaque in arteries).

Leicht’s studies also suggest that bathing is good for the heart. When body temperature is raised through physical stress, as it is in exercise or a hot bath, it triggers a short-term rise in the level of inflammatory markers, including a chemical called IL-6. “That induces a process called the ‘inflammatory response’ in which beneficial anti-inflammatory substances are released in the body,” he says.

“Since cardiovascular disease is one of many conditions that has an inflammatory component, this reaction is helpful to the heart and may offer some protection.”

The perfect warm-up

The best way to prepare for gym classes such as hot yoga — performed in rooms heated to a sweltering 33C — or for a workout in a heatwave could be to acclimatise with long, hot soaks in the bathtub. That was the conclusion of exercise scientists in the Environmental Extremes Laboratory at the University of Brighton in a study published last year in The Journal of Strength and Conditioning ­Research.

Researchers asked nine recreational runners to run 5km as fast as they could on a treadmill in a laboratory set at a temperature of 32C, and to repeat the test on different days under different conditions, acclimatising in warm temperatures beforehand for four days or pre-cooling their bodies with an ice vest. The runners were 4 per cent speedier after the pre-cooling but significantly more so when their bodies had become used to the heat, improving their performances by 6.5 per cent compared with that first treadmill run.

Not many of us have access to temperature-controlled lab conditions but lead researcher Carl James suggested that lying in a hot bath for a half-hour after a 30-minute workout also could be a way to improve your body’s tolerance to the heat.

A dip (in blood sugar)

When body temperature is warmed, as it is when you exercise, there is a rise in production of ­nitric oxide, a substance that improves blood flow and helps to carry blood sugars around the body. However, a similar response can be achieved with a hot bath.

After two weeks spent taking hour-long daily baths, the men in the most recent Loughborough study showed a reduction of fasting blood sugar and insulin levels. And in their previous trials a 60-minute hot bath produced comparable blood sugar responses to an hour of cycling (apart from after eating, when peak blood sugar was about 10 per cent lower in the bathers compared with the exercisers).

“In the long term the practice of bathing could help to reduce the risk of type 2 diabetes in susceptible individuals,” Leicht says.

“It’s not going to have an adverse effect.”

Power of a muscle soak

For those who could never quite steel themselves to plunge into an ice bath to aid recovery after intense exercise in Andy Murray or Mo Farah fashion, there is good news: a warm soak probably works better anyway.

Researchers at the Karolinska Institute in Sweden were keen to find out whether warming muscles after a workout helped them to recover power and strength more quickly. Arthur Cheng, who led the study in the Journal of Physiology, asked volunteers to perform a gruelling arm-pedalling exercise that would deplete their muscles of glycogen, the fuel for physical activity. They then repeated the task after their arm muscles had been chilled or warmed with specially designed cuffs, to assess their powers of recovery.

Results showed that they could exercise hardest when their muscles had been warmed, as they might be in a warm bath, after the first intense workout, and that the power output was worst when muscles had been cooled.

Cheng suggested that “warming muscles probably aids recovery by augmenting the muscles’ uptake of carbohydrates”.

A core workout

We all know a daily walk is among the better things we can do for body and mind, but if you really can’t fit it in, then a bath is an adequate replacement, at least in terms of calories burned. In another trial at Loughborough University, this one published last year in the journal Temperature, 14 men were asked to take an hour-long soak in a hot bath (40C) or, for the less lucky group, to do an hour of cycling.

Both activities were designed to cause a 1C rise in core body temperature in 60 minutes, during which researchers assessed how many calories they burned.

While cycling trumped bathing, a hot bath resulted in a calorie burn of 140, about the same as you would expend during a half-hour walk.

“The danger here is that people think they can just skip exercise and take a bath instead, but that’s not the case,” Leicht says.

“Exercise has far more advantages in terms of developing muscle strength and aerobic fitness, but if you can’t be active for whatever reason, then a hot bath will have some of the benefits.”

What temperature?

Guidelines suggest that bath temperature should be no higher than 43C (showers at no higher than 41C) for adults — in Kohara’s study, a hot bath was defined as 41C — and for baby and infant baths, no higher than 37C. For safety reasons, always put the cold water in first and top up with hot. However, the rule is that a bath should be comfortably hot for you.

“Everyone has a different tolerance and a lot depends on how long you are lying in a hot bath,” Leicht says.

“A lot of the participants in our study found 39C too hot when they were asked to bathe in it for an hour, so find what suits you.”

How long to stay in

The longer you soak, the better, Leicht says, although there is no magic number of minutes you need to stay in there.

“Our study looked at the extreme of a fairly hot bath for an hour, but most people wouldn’t manage that regularly,” Leicht says. “But other researchers have shown beneficial health effects from a gentler approach of three weekly baths of 20 minutes’ duration, which is more manageable.”

Leicht’s next study will look at the optimal time and temperatures for bathing.

“It could be like exercise in that a shorter, hotter and in some ways more intense bath is in some ways as a beneficial as a longer, slightly cooler bath,” he says. “That, we have yet to find out.”

The Times