Girls in homes without a biological father are more likely to hit puberty at an earlier age, say Californian researchers in the Journal of Adolescent Health. Obesity, sometimes associated with earlier puberty, was ruled out as the findings held even after the girls' weight was taken into account.
"The age at which girls are reaching puberty has been trending downward in recent decades, but much of the attention has focused on increased body weight as the primary culprit," said study author Julianna Deardorff, from the University of California - Berkeley. "While overweight and obesity alter the timing of girls' puberty, those factors don't explain all of the variance in pubertal timing."
The link between father absence and earlier puberty in girls has been found in previous research, but most of those studies relied upon recall of the girls' first periods, and few examined the contributions of body mass index, ethnicity and income.
In the new study, contrary to what the researchers expected, the absence of a biologically related father was linked to earlier breast development for girls in higher income families - those having annual household incomes of $50,000 or more. Father absence predicted earlier onset of pubic hair development only in higher income African Americans families.
The researchers say the mechanisms behind these findings are not entirely clear. Evolutionary biologists have theorized that the absence of a biological father may signal an unstable family environment, leading girls to enter puberty earlier.
Another theory that has been posited is that girls without a biological father in the home are exposed more to unrelated adult males - specifically, the pheromones of these males - that lead to earlier onset of puberty.
Another possibility is that higher income African American girls may be more exposed to certain beauty products, such as hair straighteners, which have estrogenic properties that could influence pubertal timing.
The study adds to the debate of why girls in the United States are entering puberty at an increasingly early age. A recent study found that about 15 percent of girls showed the beginnings of breast development at age 7. "In some ways, our study raises more questions than it answers," said Deardorff. "It's definitely harder for people to wrap their minds around this than around the influence of body weight. But these findings get us away from assuming that there is a simple, clear path to the earlier onset of puberty."
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Source: University of California - Berkeley