They don't care about colds - the study found more brown fat in babies who conceived in winter.
Sex in the winter often produces naturally lean people who never have to worry about their weight. On the other hand, babies conceived in the middle of summer may face a lifelong struggle to be slim.
This conclusion was reached by Swiss scientists from the University of Zurich (ETH), having examined 8,400 adults using computed tomography. The researchers linked the amount of brown fat in the bodies of people born between July and November with the data on body fat among those born between January and June.
Unlike white fat, which contributes to heart disease, cancer, and diabetes, brown fat is considered beneficial. It burns calories, generates heat, and reduces the risk of being overweight or developing metabolic disorders. In adults, there is a small amount of brown fat, mainly under the tongue, around the collar and along the spine.
Scientists have linked the concept of cold weather conception to higher amounts of brown fat in both mice and humans.
To test their assumptions, they conducted experiments on mice, which were forced to mate at cold and very warm temperatures. The results confirmed the hypothesis and showed that the difference in temperature only affects sexually active males.
The offspring of male mice kept in a cool environment at 8 degrees Celsius for several days prior to mating had a higher amount of brown fat. It was also better protected against weight gain and metabolic disorders when fed high-fat foods.
Previous research has shown that people living in colder regions of the world tend to have higher levels of brown body fat.
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Professor Christian Wolfrum of the University of Zurich ETH, who led the study, said: “So far, the assumptions about the amount of brown fat have had something to do with ambient temperatures. But our observations show that temperatures before conception can also affect later brown fat levels.”
Professor Wolfrum also warned against hasty conclusions and attempts to put into practice the results of the study: “Apparently, exposure to cold should be carried out for a longer period, so that it could affect epigenetic programming. Dip in cold water or short walks on the ice will probably not be enough."
The study was published in the journal Nature Medicine.
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