It's a stereotype universally acknowledged that a woman at room temperature must be in want of a coat. But is it a scientific truth?
Sheer observations aside, very few controlled studies have investigated how male and female bodies withstand cold temperatures.
A new study has surprised researchers at the US National Institutes of Health (NIH), finding no sex difference in the perception of a cold room, and very few sex differences in our physiological response to it.
During the trial, a group of 28 men and women spent five hours in a temperature-controlled room, wearing provided shirts, shorts or skirts, and socks. Each day, participants were physically monitored and surveyed on their comfortability as the temperature ranged between 17 ºC to 31 ºC.
Contrary to what NIH researchers were expecting to find, women in the study had a slightly higher core body temperature in colder temperatures than men.
There were no sex differences in glucose uptake, muscle electrical
activity, skin temperature, or cold-induced thermogenesis.
It seems that even though female participants were physically smaller than males, producing less body heat overall, their relatively higher body fat helped balance the scales.
Based on their results, researchers at NIH say the female body's comfort zone for temperature bottoms out at roughly 22 °C – a degree lower than the average for male participants.
This suggests that as temperatures drop, the female body doesn't have to expend energy for warmth as soon as the male body, giving women a more "arctic" thermal profile.
But that sex difference, while it is significant, offers little advantage. As temperatures lower to 17 ºC, researchers found no sex differences in the onset of shivering or how comfortable or uncomfortable participants said they felt in the room.
In the past, scientists have suggested that women get colder at higher temperatures than men because of physiological sex differences, such as lower heat production, greater heat loss, or greater heat demands. But none of these hypotheses quite fit the recent results.
One small study isn't likely to end the debate, but perhaps it's time to move beyond observational studies and general consensus and start to dig into the real science.
To this day, there are very few studies that have rigorously tested sex differences in thermoregulation. In fact, historically the whole field of human physiology has focused mostly on the male body, using it as a default for all of humanity.
Having such a restricted, or even binary, approach misses a big part of the picture. Hormonal changes and medications, for instance, can also impact how a person responds and perceives temperature changes, and these factors, in turn, can be influenced by a person's sex or gender.
"The principal contributors to individual differences in human thermoregulation are physical attributes, including body size and composition, which may be partly mediated by sex," conclude researchers at NIH.
"These findings should be replicated in larger, more diverse study samples to enhance generalizability."
The study was published in PNAS.