People born in September, October and November are more likely to be skinnier and have less fat around their organs compared to those born in April and May, a study suggests.
Experts have discovered that individuals conceived in colder seasons show higher activity in their brown adipose tissue – the type of fat that burns calories to produce heat.
This leads to increased energy expenditure, a lower BMI and less fat accumulation around internal organs, they found.
The coldest months of the year are typically December, January and February, meaning those born in September, October and November are more likely to have this advantage.
Meanwhile the warmest two months – typically July and August – correspond to a birthday in April or May.
The team said their findings suggest that atmosphere and weather can influence human physiology.
Researchers from Tohoku University Graduate School of Medicine in Japan analysed 683 health male and female individuals aged between three and 78.
They were placed into two categories depending on what time of year they were conceived.
The study found that people whose parents were exposed to colder temperatures during their conception had increased activity in their brown adipose tissue – a type of fat that burns calories to create heat
The split was between those whose parents were exposed to cold temperatures immediately prior to and including conception – between 17 October and 15 April – and those whose parents were exposed to warmer temperatures between 16 April and 16 October.
Analysis revealed individuals who were conceived during colder seasons showed higher brown adipose tissue activity.
This was linked to increased energy expenditure, increased thermogenesis – the process by which the body generates heat by burning calories – lower fat accumulation around the organs and lower BMI into adulthood.
A key factor in determining brown adipose tissue activity was parents being exposed to a large diurnal temperature range – the difference between the highest and lowest temperatures within a 24-hour period – and lower average temperatures in the time immediately before conception.
Writing in the journal Nature Metabolism, the researchers said the findings indicate that brown adipose tissue activity is ‘preprogrammed’ by exposure to cold temperatures before fertilisation.
They propose that the driver for this may come mostly from the father’s exposure to colder temperatures, rather than the mother.
It has previously been suggested that cold exposure leaves a signal in sperm that – when passed on during fertilisation – triggers the development of an embryo that is better adapted to metabolism and cold temperatures.
Commenting on the study Raffaele Teperino, from the German Research Center for Environmental Health, said: ‘Parental health during conception and gestation can affect offspring development and health.
A bulging waistline and high BMI affect a huge proportion of Brits today, with more than a quarter of adults thought to be obese
‘A study in humans now shows that adult individuals who were conceived during cold seasons exhibit greater brown adipose tissue activity, increased energy expenditure, lower body mass index and lower visceral fat accumulation
‘The new findings emphasize once more the critical role of the preconception environment in shaping offspring metabolism and offer perspectives for understanding the co-existence of two global health challenges – obesity and warming.’
Data suggests that the number of obese children and adults in the UK will rise substantially by 2050.
The most comprehensive global analysis to date predicts that children as young as five will be much more likely to be obese in the coming decades.
It shows that for children aged five to 14, obesity will rise from 12.0 per cent of girls in 2021 to 18.4 per cent in 2050, and from 9.9 per cent to 15.5 per cent in boys over the same period.
The estimated prevalence of obesity for 15 to 24-year-olds is 15.4 per cent in 2021 among girls, rising to 22.9 per cent in 2050.
The data further shows that obesity in adults aged 25 and over will jump from 31.7 per cent of women in 2021 to 42.6 per cent in 2050, while obesity in men will rise from 29.3 per cent to 39.5 per cent.
Responding to the findings, published in the Lancet medical journal, experts said the global picture represents a ‘profound tragedy and a monumental societal failure’.
