Getting a bit chilly or overly warm may not be comfortable, but it can be healthy, research now suggests. And that's especially true for people who carry too much body fat or who suffer from type 2 diabetes.
These temperature benefits have to do with our metabolism — the set of life-sustaining chemical reactions at work inside cells. The faster someone’s metabolism, the more calories a body will burn. Burn more calories than you ate and you will shed some pounds.
Being mildly cold speeds up your metabolism. In other words, it forces the body’s furnace to stoke up. It does this to help the body maintain a healthy temperature of around 37° Celsius (98.6° Fahrenheit).
In people with type 2 diabetes, exposure to mild cold also improves the way their bodies respond to sugar. Unless their disease is controlled, it can boost the risk of heart disease, coma — even death.
Wouter van Marken Lichtenbelt is a biologist in the Netherlands at Maastricht University. He studies how environmental factors, such as temperatures, influence human health. Mild cold and heat can help manage both obesity and diabetes, he says. He came to this conclusion after poring over data from a range of studies that he and others have done. His team detailed its reasoning in a paper published April 26 in Building Research & Information.
As a review paper, its authors sifted through a host of published data by research teams across the world to see if any useful trends emerged. In some cases, these trends may not have shown up in individual papers, but only by looking at a host of related ones on a particular topic.
Most research about temperature's effect on the human body has focused on extremes of hot and cold. Van Marken Lichtenbelt instead homed in on impacts of milder variations in temps experienced in everyday life. Such findings are important, he argues, because people spend a lot of time indoors. Most buildings and homes are set to a constant and comfortable temperature, around 21 to 22 °C (69.8 to 71.6 °F).
But the patterns his team extracted from looking at lots of research now suggest that "we should not assume comfortable is always healthy,” he says. “Sometimes you have to get out of your comfort zone."
Sifting through the data . . .
One study that contributed to this conclusion was published in 2013 by van Marken Lichtenbelt’s group. It had exposed 17 healthy people in their early 20s to mild cold. Over the course of 10 days, these recruits spent an increasing number of hours in a temperature-controlled room. Its thermostat was set at 15 °C (59 °F).
The volunteers had to spend two hours in the room on the first day and four hours on the next. Every day after that, everyone stayed in that chilly room for six hours.
"Most subjects were slightly shivering at the start, but less so at day 10," recalls van Marken Lichtenbelt. More importantly, by day 10, their metabolisms had sped up. These people burned about 30 percent more calories, on average, than they had before the experiment had begun.
That energy to keep the body temperature uniform came largely from the body's store of brown fat, van Marken Lichtenbelt showed. Normal body fat is white. As brown fat’s name suggests, this type looks a bit dark. More importantly, it functions differently than white fat.
White fat is what the body makes from excess fuel (food) for which the body has no immediate need. This white fat can be burned as energy. But mainly it just sits around like a kitchen pantry, becoming a storehouse. The body only turns to it as a reprieve from extreme hunger — what you’d think of as starvation.
Brown fat, in contrast, doesn’t convert its stored fuel into heat when someone is starving. Cold temperatures activate it. Regular exposure to mild cold seems to kick start the body's burning of brown fat. And this is true whether someone is fat or lean. However, brown fat tends to be less active in obese people. So reigniting it with cold temps might be a strategy to help those who are overweight slim down.
There is less research on the effects of mild heat. The few studies that exist suggest its effect on the body is not as dramatic as chilly temps, says van Marken Lichtenbelt. Any boost seen in metabolism probably reflects the fact that the heart speeds up when the body gets too warm.
Chilly temps: Therapeutic for diabetics?
In 2015, van Marken Lichtenbelt’s team asked people with type 2 diabetes to endure the same chilly conditions as the healthy participants had in the earlier study. All eight people were in their 50s or 60s (an age at which type 2 diabetes tends to emerge). And cool indoor temps showed signs of helping them.
Type 2 disease is characterized by the body’s inability to manage sugar properly. Normally insulin shepherds that sugar into cells where it can fuel their activities. But in this disease, the body begins resisting — partially ignoring — that hormone. When this happens, high levels of glucose (a type of sugar) will accumulate in the blood. And that’s bad for blood vessels and more.
After 10 days of exposure to the mildly cold indoor temps, the scientists tested their participants' blood. It showed that their insulin now worked 40 percent better than it had before the study began. That means their bodies were better able to process sugar. The researchers aren't exactly sure why this happened. They do, however, suspect it too had something to do with activating the body's brown fat.
In any case, the 40 percent improvement in insulin sensitivity is significant. It’s similar to what van Marken Lichtenbelt and his colleagues saw in another study of diabetic patients who were taking medicine and exercising.
What should people make of all this?
Studies such as these show that it’s important to move between different temperature zones, concludes Susan Roaf. She is an architect in Scotland who specializes in adapting buildings to different climates. Roaf works at Heriot-Watt University in Edinburgh and was not involved with these studies.
Moving between different indoor temperatures helps to make sure our body's system for regulating temperature — including its burning of brown fat — stays healthy, she says.
"Respect your deep core temperature and the systems that keep it stable," Roaf recommends.
A good place to start is at home or work, van Marken Lichtenbelt says. Turn the temperature down or up. "Indoor air temperatures are not going to save the world," he says. However, he adds, this “is one lifestyle factor that could improve our health.”
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
brown fat A type of stored fat that the body burns when it senses a strong need to heat up the body (owing to being in a cold environment). It takes its name from the actual color of the fat, which is not light colored as the more common “white” body fat is. The storage of excess calories as this type of fat, and its later use by the body, are controlled by nervous system.
calorie The amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. It is typically used as a measurement of the energy contained in some defined amount of food.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.
chemical reaction A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).
climate The weather conditions that typically exist in one area, in general, or over a long period.
colleague Someone who works with another; a co-worker or team member.
core Something — usually round-shaped — in the center of an object.
factor Something that plays a role in a particular condition or event; a contributor.
fat A natural oily or greasy substance occurring in plants and in animal bodies, especially when deposited as a layer under the skin or around certain organs. Fat’s primary role is as an energy reserve. Fat also is a vital nutrient, though it can be harmful if consumed in excessive amounts.
fuel Any material that will release energy during a controlled chemical or nuclear reaction.
hormone (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body.
insulin A hormone produced in the pancreas (an organ that is part of the digestive system) that helps the body use glucose as fuel.
metabolism The set of life-sustaining chemical reactions that take place inside cells and bigger structures, such as organs. These reactions enable organisms to grow, reproduce, move and otherwise respond to their environments.
obese Extremely overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.
range The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.
recruit (in research) New member of a group or human trial, or to enroll a new member into a research trial. Some may receive money or other compensation for their participation, particularly if they enter the trial healthy.
review paper (in science publishing) A paper that reviews the data and findings in a broad body of work by many research teams. This may include 50 to 200 different research studies or more. The authors then synthesize the findings, looking for patterns that may emerge from the data. These patterns may strengthen — or weaken — the conclusions that seem reasonable when considering just a single paper or two.
risk The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)
subjects (in research) The participants in a trial. The term usually refers to people who volunteered to take part. Some may receive money or other compensation for their participation, particularly if they entered the trial healthy.
type 2 diabetes A disease caused by the body’s inability to effectively use insulin, a hormone that helps the body process and use sugars.
Journal: W. van Marken Lichtenbelt et al. Healthy excursions outside the thermal comfort zone. Building Research & Information. Published online April 27, 2017 . doi: 10.1080/09613218.2017.1307647.
Journal: P. Schrauwen and W.D. van Marken Lichtenbelt. Combatting type 2 diabetes by turning up the heat. Diabetologia. Vol. 59, November 2016, p. 2269. doi: 10.1007/s00125-016-4068-3.
Journal: M.J. Hanssen et al. Short-term cold acclimation improves insulin sensitivity in patients with type 2 diabetes mellitus. Nature Medicine. Published online July 6, 2015. doi: 10.1038/nm.3891.
Journal: A.A. van der Lans et al. Cold acclimation recruits human brown fat and increases nonshivering thermogenesis. Journal of Clinical Investigation. Vol. 123, August 2013, p. 3395. doi:10.1172/JCI68993.