Central heating could be contributing to obesity

“Overheated homes and offices adding to weighty problem,” The Daily Telegraph reports. Dutch researchers have argued that the widespread use of central heating stops people’s bodies using up energy to stay warm, which could be helping drive up obesity levels.

They make the case that the default setting of most indoor environments, homes, offices and hospitals, is at a ‘Goldilocks level’ (“hot, but not too hot”).

Turning down the heating in homes, offices and hospitals may help us burn more calories and stay slim, they say.

Similar to exercise training for health, the researchers advocate “temperature training” as part of a healthy lifestyle, allowing us to get used to the sort of temperature that our ancestors would have found comfortable.

What type of paper is this and who produced it?

This was a narrative review on the topic of cold exposure, energy expenditure and its relationship to obesity. This type of review discusses the literature on a particular topic and as is the case here, may use certain studies in support of a particular argument.

The authors do not appear to have searched the literature in a systematic way (a systematic review) nor do they report on how the search for literature was carried out. There is a risk that important evidence may have been overlooked or ignored.

The paper was written by researchers from Maastricht University and Avans Hogeschool, both in the Netherlands, and published in the peer reviewed journal Science and Society.

What points does the paper make about temperature regulation and weight?

The paper points out that over the past century we have become better at controlling temperature and in the West, are able to cool and heat our offices, homes, hospitals and factories for maximum comfort – minimising the body's energy expenditure necessary to control internal temperature.

The rise in obesity they say is linked not only to excessive food intake but also to physical inactivity (reduced energy expenditure), so the health aspects of living at warmer temperatures deserve to be examined.

They mention that when it is cold enough, we start shivering and start burning energy at a greatly increased rate – up to five times quicker than we would normally.

Obviously, spending long periods in shiveringly cold home or work environments would be both unpleasant and unhealthy. It is also hard to see whether people would get much work done when their fingers were shivering too much to control machinery, work a keyboard or serve presumably chilly customers.

Cold but not shivering

So instead, they focus on “non-shivering thermogenesis” (NST), a method of keeping warm which does not entail shivering. NST activates brown adipose tissue (BAT), more popularly known as brown fat. The role of brown fat activity is to generate heat in animals and newborn babies that are not able to shiver.

The authors say there is evidence that NST also exists in adult humans and can potentially affect energy balance. In young and middle-aged people, non-shivering heat production can account for up to 30% of the body's energy budget, they say. That means lower temperatures can significantly increase the amount of energy a person expends overall, without any shivering involved.

Carefully acclimatising people to colder temperatures has been shown to reduce the shivering method of keeping body temperatures up and produce the NST means of keeping warm through brown fat activity. It has also been shown to decrease body fat.

They suggest that a mildly cold temperature indoors (for example, 18-19 degrees C) can result in the same increases in NST. This roughly corresponds to the average outdoors temperatures during June in England.

At present, they say, people are exposed to relatively high indoor temperatures in winter, especially in care homes and hospitals, with the result that, “entire populations may be prone to developing diseases such as obesity.” Lack of exposure to varied temperatures in line with the external climate and the seasons, means people also become vulnerable to sudden changes in temperature such as during cold spells, when death rates rise from cardiovascular disease, lung diseases and cancer. Aside from the negative impact on health this leads to high energy consumption.

Temperature training?

Similar to exercise training for health, they advocate “temperature training” as part of a healthy lifestyle, with people regularly exposed to cool conditions. People are able to feel comfortable in lower temperatures, they argue and the body spends more energy in keeping body temperature stable without shivering.

There is now evidence to suggest that a more variable indoor temperature – one allowed to “drift along” with temperatures outside – might be beneficial, although long-term effects still await further investigation.

What evidence did the researchers look at?

The researchers looked at a range of evidence to support their argument, including:

studies in rodents
physiological studies in humans on NST and its relationship to heat production
studies in humans on cold acclimatisation and its relationship to brown fat activity and decrease in body fat
studies on the regulation of indoor temperatures and temperatures which people find comfortable

In particular, they quote research from Japan that they say found a decrease in body fat after people spent two hours per day at 17oC (62.6oF) for six weeks. The team also say their own research found that people get used to the cold over time. After six hours a day at 15oC (59oF) for a period of 10 days, people in a study felt more comfortable and shivered less.

Importantly, as this was not a systematic review, we are unable to consider what parameters the researchers used when searching for evidence and what evidence they considered but then rejected, for whatever reason.

This is why systematic reviews have more “weight” in terms of evidence than narrative reviews.

Should I turn down the heating?

Slightly turning down the thermostat could certainly help your “energy balance”. There is a certain logic to the theory that if you’re cold the body will use energy to stay warm. But as yet there is no hard evidence to suggest this will help you stay a healthy weight.

Staying warm in winter is important for health, especially for those who are vulnerable to cold such as the elderly and people with chronic conditions such as asthma. Current advice is that indoor heating should be around 18-21oC.

Maybe one way to combine the benefits of temperature and physical activity is to regularly take brisk walks or jogs during the winter months. While this may not be a guaranteed method of burning of your brown fat, it should help contribute towards your fitness levels and lift your mood.

And whether the same happens with turning down the air conditioning in hot climates is a matter for heated debate (sorry – Ed.).