Girls born to obese moms far more likely to start puberty early, study finds

Girls born to obese mothers are more likely to start puberty early than daughters of normal-weight or underweight mothers, new research finds.

The study, published today in the American Journal of Epidemiology, involved more than 15,000 girls ages 6 to 11 in Northern California, using doctors' records of children's development for the analysis.

The normal age for girls to start puberty is between 8 and 13 years old, with early puberty defined as beginning when a girl is younger than 8.

The research -- when adjusting for factors like the mother's age, ethnicity and education level when she gives birth, and whether she smokes -- found that early puberty was 39 percent more likely among girls born to obese mothers, and 21 percent more likely among those with overweight mothers.

The gap was even larger when comparing girls of overweight and underweight mothers. Daughters of overweight mothers started puberty on average seven months earlier than those with underweight mothers.

It is already known that a mothers’ weight can affect the weight of her children.

But this is the first large-scale study showing that it may also affect the age at which a daughter reaches puberty. Researchers think the association might be related to fetal development in the womb.

“What we are learning is that the in-utero environment may affect the timing of future pubertal development” Ai Kubo, a research scientist at Kaiser Permanente in Northern California and one of the authors of this study, said in a press release. “[This] makes sense since human brains are developed in utero and the brain releases hormones affecting puberty”.

Early puberty can be associated with a number of health problems.

Girls who undergo puberty early are known to experience higher rates of depression and anxiety. Later in life they are more likely to be diagnosed with diabetes, cardiac conditions and some breast and reproductive cancers.

However, this study did not follow girls who had puberty early for years or measure the rates at which they suffered such health problems. Researchers also looked only at the age girls started puberty, not the time taken to complete it.

When comparing groups of girls based on ethnicity, the study found that the association between a mother's weight and a daughter's age at puberty onset was strongest for children of Asian ethnicity. Girls born to overweight Asian mothers were 53 percent more likely to start puberty early compared to daughters of Asian mothers of normal weight.

American girls in general have begun in recent years to start puberty at younger ages, partly because of higher rates of childhood obesity.

However, the average age of puberty has fallen also for children who aren’t overweight, leading doctors to think that other factors besides a girl's weight may be involved.

Although this study adjusted for several factors -- including the child’s weight before puberty and the mother’s age and whether she smoked -- it isn't certain that every possible factor which could affect the onset of puberty was accounted for.

The research also found that girls born to mothers with hyperglycemia, a high blood-sugar level, were more likely to start puberty early.

Interestingly, no such association was found when mothers had gestational diabetes, a condition in which blood-sugar levels rise temporarily during pregnancy. Researchers think this might be because the women with this diagnosis took extra care of their health.

“It’s possible that women with the diagnosis of gestational diabetes were more careful about weight and diet, which might have changed the amount of weight gain,” Kubo suggested.

George Gillett is a medical resident affiliated with the University of Oxford working in the ABC News Medical Unit.