I know this is a stereotype, but your grandmother/father/grumpy uncle/whoever in your life fits this anecdote was right: if you’re cold, put on a sweater. Growing up, my family was not so economical with the temperature control in our house, and I can remember the specific pleasure of curling up with a good book next to the gas fireplace until my back began to sear with heat. Even now as I write, I am abating the cold (September!) grimness of London, England with the cosy warmth that only central heating can provide. You may be a person of creature comforts like me – and I know that many of you Generation Y Yuppies are – or you may be a little bit more puritanical. But regardless, some new research findings might make you think a little bit.
The new research comes from a pair of studies – one from Japan and one from the Netherlands – about brown adipose tissue, or fat (1, 2). What is brown fat ? As opposed to white fat, which lies under the surface of our skin and when in excess marks a person as overweight or obese, brown fat is a highly metabolically active tissue found in small amounts in the neck, upper back, and clavicles (3, 4). Aside from knowledge of its anatomic presence, little was known about brown fat in humans until the past few years. The new study from the Netherlands found that brown fat plays a role in what’s called ‘nonshivering thermogenesis’ – it burns calories to generate heat from within our bodies during exposure to cold (5). The researchers subjected a group of people to a 10-day cold acclimation programme (exposure to 15-16 degree C temperature for 6 hours per day), and found significant increases in brown fat metabolic activity and less shivering among the participants, who reported feeling less sensitive to cold at the end of the study (2). Therefore, regular exposure to cold makes brown fat more efficient in keeping us warm – it achieves this through increased nonshivering thermogenesis, resulting in less of a need to shiver.
This information makes sense – we all have experienced getting used to colder and warmer temperatures. But, let’s think about brown fat in the context of the so-called obesity epidemic that has emerged in Western countries. One contributor among many may be the ubiquitous regulated indoor temperatures privileged upon us by technology. With less exposure to cold, brown fat cannot be activated to burn at its metabolic potential (4). Of course, diet and exercise are major factors. Middle income countries such as Mexico that have warmer climates than many of the rich, Western countries are experiencing rising obesity rates that are unlikely to be due to artificial home heating. But regardless of any speculation about the causes of obesity, brown fat has incredible potential to reduce obesity in the population.
In the Japanese study, the investigators exposed health human subjects to cold (17 degrees C) for two hours per day for 6 weeks (1). They found an increase in brown fat activity and energy expenditure, and a decrease in body fat mass at the end of study (1). This means that getting brown fat active through cold exposure is actually effective in reducing body fat. Of course, this is good. We are not concerned with the ability of brown fat to keep us warm, as cold exposure is not really a health concern nowadays, but, we are interested in whether it can help combat the obesity epidemic (4). The trouble is that brown fat has to be activated by cold to become metabolically active: i.e. you have to be a cold place for brown fat to start burning calories for you. The authors of both the Japanese and Dutch studies conclude that regular exposure to colder temperatures could be effective in reducing the prevalence of obesity in the population.
Therefore you should keep your hand off the thermostat. Let yourself be slightly cold – just outside of the comfort range that the human body is physiologically conditioned to remain at, which is around 23 degrees C (3). There’s no need to torture yourself – around 17 degrees C will suffice. You will burn calories, and according to the scientific evidence, you will eventually get used to it and feel the cold less. And hey, you will definitely save money on heating while helping out the environment at the same time. That’s a self-congratulatory pat on the back that any self-respecting Generation Y can get on board with, right? The next steps are vegetarianism, regular gym attendance, and a bicycle in place of car. If you’re already there, gold star for you, and if not, well, you’ve managed to read through yet another internet argument to be healthy and environmentally friendly, so my mission here has been achieved.
1) Yoneshiro T, Aita S, Matsushita M, Kayahara T, Kameya T, Kawai Y, et al. Recruited brown adipose tissue as an antiobesity agent in humans. J Clin Invest 2013;123(8):3404-8.
2) van der Lans AAJJ, Hoeks J, Brans B, Vijgen GHEJ, Visser MGW, Vosselman MJ, et al. Cold acclimation recruits human brown fat and increases nonshivering thermogenesis. J Clin Invest 2013; doi:10.1172/JCI68993.
3) Hutchinson A. Want to burn body fat? Step up to the thermostat. Globe and Mail. 08 September 2013. http://www.theglobeandmail.com/life/health-and-fitness/fitness/want-to-burn-body-fat-step-up-to-the-thermostat/article14171995/
4) Cannon B, Nedergaard J. Yes, even human brown fat is on fire! J Clin Invest 2013;122(2):486-9.
5) Cannon B, Nedergaard J. Brown adipose tissue: function and physiological significance. Physiol Rev 2004;84(1):277-359