Researchers have claimed that having sex in the winter may help protect children against weight and metabolic disorders after they are born.
In a study published in Nature Medicine, scientists from ETH Zurich in Switzerland suggest that men who spend time in low temperatures prior to having sex produce more brown adipose tissue in their sperm, which is passed on to their offspring.
Also known as brown fat, this tissue – found under the tongue, around the collarbone, or along the spine – helps people use up excess energy. Higher rates of brown fat has been linked with a lower risk of becoming overweight or developing metabolic disorders.
“Until now, the assumption was that this had something to do with the temperatures people experienced during their lifetime,” Professor Christian Wolfrum, who led the study, said in a statement. “[B]ut our observations suggest that temperatures prior to conception might also affect later levels of brown fat.”
In the study, the team analyzed computer tomography (CT) images of 8,400 adult patients. They found that people born between July and November in the Northern Hemisphere, thus conceived around winter, had much more brown fat than those born between January and June – and thus conceived in the warmer part of the year.
They then carried out a study in mice to confirm the findings, keeping some at a moderate temperature of 23°C (73°F) and others at 8°C (46°F), and allowing them to mate. While the temperature of the females did not affect brown fat levels, the males kept in a cool environment for several days produced offspring with more brown fat than the others.
The offspring of those males in cool temperatures went on to gain less weight when placed on a high-fat diet. These mice were also better at regulating their body temperature in cold conditions, a possible evolutionary benefit arising from conception.
The findings appear to suggest that the ambient temperature at conception can lead directly to epigenetic changes in offspring. Interestingly, it may also in part explain the rise in obesity in the US, where average indoor temperatures have risen over the past few decades.
But the researchers caution you probably shouldn’t go frolicking in the snow just yet. They note they need to study this correlation further, and suggest the exposure to cold may need to take place over a longer period than just jumping in an icy bath.
It’s not all good news for winter just yet, either. Last year, a study found that women who gave birth in winter – and thus conceived in warmer temperatures – were less likely to suffer from postpartum depression (PPD). Summer months, meanwhile, have previously been linked to better weights for babies.