Science is at its most powerful when it reveals to us some new unknown about the universe. Science is perhaps at its most satisfying, however, when it confirms for us something we sort of knew to be true all along. This is especially true when those suspicions are based on the loose grounds of personal experience. Recently, I had been cobbling together a new temperature theory based on some autumnal experiences with my wife, when, by good fortune, Jenny Visser's team at Erasmus University Medical Center in Rotterdam, The Netherlands, published a paper, the results of which directly supported my theory.
The theory has to do with temperature preference, a topic that in our household tends to flare up in autumn. As the air temperature falls and the thermal gradient steepens, the activity around our thermostat reaches its annual peak. These thermostat adjustments are usually done on the sly because my wife and I prefer different temperatures: she prefers it warm and I prefer it, well, not quite as warm. I've polled friends and family on the topic and the results hinted that males and females may indeed defend their own sides of the thermostat. The work of the Rotterdam team added some welcome rigour to this theory.
The team investigated the thermal perceptions and shivering thresholds of 20 men and 23 women participants. The experimenters outfitted each participant with skin temperature sensors and shiver-detecting electromyography electrodes, and then wrapped them in a precise temperature-controlled thermal blanket and vest. They then gradually dialed down blanket and vest temperatures from 24°C to 9°C over 45 minutes and let the sensors and electrodes do the rest. As the temperature gradually fell, the team asked the participants to score their thermal sensation and comfort on seven-point scales ranging from ‘hot’ to ‘cold’ and ‘very comfortable’ to ‘very uncomfortable’, respectively.
The results revealed that women felt cold at higher experimental temperatures than men did (18.3 versus 14.6°C). Previous work has shown that temperature-sensitive TRPM8 receptors on the skin are more sensitive in women than men, and the Rotterdam team suspects these receptors are at play here too. Beyond just feeling cold, women began shivering at higher temperatures than men (11.3 versus 9.6°C). The way in which skin temperatures fluctuated across the sensors signified to the team that women maximally constrict surface blood vessels at higher temperatures than men do, indicating women begin losing body heat at higher temperatures than men and consequently supplement that lost heat with shivering. As for why women begin losing heat at higher temperatures than men, the team implicates physics; the women in their study – like women generally – had higher body surface area-to-mass ratios, meaning each gram of heat-producing tissue had a larger surface area over which the heat it generated could be lost. The result was higher rates of heat loss and, therefore, higher temperatures at which the body started compensating by producing extra heat through shivering.
These results have timely implications both generally and personally. Generally, climate change-related studies often include experimental temperature change protocols similar to those used by the Rotterdam group. If their results show sex-specific variation in temperature responses, so too might those of other studies, indicating male and female conspecifics may respond slightly differently to climate change. And personally, I have been a little more careful when defending my side of the thermostat this autumn because, as my wife now reminds me, what I am quibbling with is an actual physical law: surface area-to-volume scaling. It's easy to quibble about some things; physical laws aren't one of them. I'm anticipating a warm winter.