Babies conceived in winter less likely to become obese adults, Japan study finds

South China Morning Post

10-04-2025

Babies who are conceived in winter are less likely to gain weight in adulthood, according to a group of researchers led by a Japanese university, whose findings may lead to new ways of preventing obesity and lifestyle-related diseases.
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The Tohoku University-led team examined two types of body fat – white fat, which stores energy, and brown fat, which produces heat by consuming energy – in the study published in the Nature Metabolism magazine on Tuesday, according to a report by The Japan Times newspaper.
When body temperatures fall, brown fat induces the body to burn fat. As such, individuals who have more active brown fat would find it easier to keep their weight down.
For their study, the researchers analysed the brown fat of 356 Japanese men between the ages of 18 and 29 who were categorised based on the months they were conceived.
They found that brown fat was more active among the men who were conceived during the colder months between October 17 and April 15 than those conceived during the warmer months.
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The team also looked at where the men's mothers were living and the weather then and noted that higher brown fat activity was linked to lower external temperatures before fertilisation and a bigger difference in daily temperature.