We all know babies grow up fast. But are female children also speeding into adolescence earlier? The short answer is: probably. A recent study in the US journal Pediatrics concluded that girls are now likely to enter puberty sooner than previously known. The researchers looked at seven-year-old girls from different ethnicities and found that 10 per cent of whites, 15 per cent of Hispanics and 23 per cent of black non-Hispanic girls showed breast development in keeping with the onset of pubertal hormones. This chimes with European studies examining trends in the arrival of menarche, or the age of a girl’s first period. This has fallen from 13.72 in 1925 to 12.83 among girls born in the 1960s. In a 1980s study of British children, 12 years and 11 months was the median menarcheal age.

So, what is the significance of an earlier onset of puberty in girls? As a student I learnt that the most likely cause was improved nutrition. But perhaps we now feed our children too well. Weight is a known predictor of puberty – indeed, one theory is that weight itself triggers puberty, once it reaches a threshold. Obesity causes a hormonal kick-off, and girls who are heavier at seven are more likely to start their periods early.

If the idea of a younger child dealing with the psychological consequences of earlier puberty is unappealing, there are other problems too. Earlier menarche has been associated with increased risk of breast cancer, the rationale being that longer exposure to oestrogen over a lifetime has damaging consequences. Earlier menarche is also associated with heavier weight as an adult and also, probably via this mechanism, diabetes.

It’s tempting to conclude that this is all a product of an age of obesity. The truth is more complex. Age at menstruation is also related to birth size, prematurity and the mother’s age. If a mother had an early menarche, her children are more likely to be overweight. So menarche may be partly genetically predicted, but there is other work demonstrating that high levels of psychosocial stress are associated with early puberty.

Studies have indicated that weight gain in childhood interacts with genetic risk for menarcheal age. It is not the case that childhood obesity is simply the cause of earlier puberty, therefore. Instead, the interactions between genetics, environment and weight are intertwined.

One can see how social inequality could be transmitted between generations; now, it seems, hazards that might have been mitigated by improved circumstances are still resulting from past events. Untangling that is going to take a while. In the meantime, enjoy your children while you can.

Margaret McCartney is a GP in Glasgow

margaret.mccartney@ft.com

To follow Margaret’s blog, go to www.margaretmccartney.com/blog

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