Higher Room Temperature May Contribute to Obesity

Summary
Obesity is generally caused by reduced calorie expenditure and increased calorie intake. The present review looked at the tendency of setting indoor temperatures higher, reducing cold exposure and its effect on obesity. Reduced cold exposure reduces efficiency of utilization of energy obtained from food. Thus, a causal relationship between staying in an indoor “thermal comfort zone” and weight gain seems possible. “Reduced exposure to seasonal cold may have a dual effect on energy expenditure, both minimizing the need for physiological thermogenesis and reducing thermogenic capacity,” states the authors. However, more direct studies in humans are necessary before making a concrete conclusion.

Introduction
Obesity is a serious health problem in populations in Western developed countries. There are genetic and environmental causes of obesity. Environmental trends, like eating high calorie diets and leading a sedentary lifestyle, have received attention. However, other environmental factors, like cold exposure, have not been studied. There is a trend in keeping indoor temperatures higher compared to the past. “Prolonged exposure to temperatures below the human thermoneutral zone…increases energy expenditure, and therefore has the potential to affect energy balance over time. There is also evidence that low ambient temperatures can affect the body’s ability to maintain energy balance by increasing the capacity for thermogenesis.” Whether this can promote obesity is the question. The present study reviewed published research literature and tried to provide an answer.

Methodology
* This review of previously published research consists of an analysis of results of different studies.
* The present review focused on four themes:
1. Current trends of indoor winter temperatures in the Western world.
2. The role of brown fat tissue in humans in keeping the body warm.
3. Modifications of brown fat tissue function in cold and warm temperatures.
1. The effect of higher room temperatures on energy obtained by eating specific food.

Results
* There is a trend to keep indoor temperatures higher. In the UK, the average living room temperature rose from 65 F in 1978 to 66.4 F in 1996. Bedroom temperatures increased from 59.4 F to 65.5 F in the same period. In the U.S., winter nighttime bedroom temperatures rose from 19.3°C to 20.2°C between 1987 and 2005.
* The human body adapts to the cold by producing internal heat, generated by brown adipose (fat) tissue. Cold environment leads to more brown fat accumulation in adults than the usual yellow fat.
* In laboratory animals and humans, exposure to cold promotes the use of excess energy obtained from food. If this cold exposure is absent, effective utilization of energy from food does not occur. In animals, easy availability of tasty food promotes overeating. This may be true for people in the developed world.
* Thus, exposure to a cold environment increases energy expenditure and decreases deposition of yellow fat. Obesity occurs when yellow fat is deposited in the body in excess.

Shortcomings
The research indicates a possibility of a causal link between increased amounts of time spent in a “thermal comfort zone” and increased obesity in the population. But these are indirect conclusions. Effects of other factors, like the use of warm clothes in indoor settings and decreased appetite in higher ambient temperatures, were not considered. As yet, there have been no direct studies of effects of long-term thermal environment on body weight in humans.

Conclusion
Increased energy expenditure due to exposure to mild cold for just 10 percent of the time, will lead to an 17.5 lb. weight difference in 10 years. In adults, reduced exposure to cold environment produces less active brown fat. Less brown fat means inefficient utilization of energy obtained from dietary food. Living in centrally heated or air-conditioned rooms, and using heat controlled vehicles and offices, might be additional factors for increased obesity in the Western population. “Establishing the significance and magnitude of the effects of both short-term and long-term thermal exposures on body weight could lead to the development of novel therapies to address obesity on an individual and a population level.”

For More Information:
Setting the Thermostat High during Indoor Heating Might Mean a Gain in Weight
Publication Journal: Obesity Reviews, 2011
By F. Johnson; A. Mavroggiani ; Department of Epidemiology and Public Health and the Bartlett School of Architecture, University College London, UK

*FYI Living Lab Reports Are Summaries of the Original Research.

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