By Catherine Donaldson-Evans of AOL Health
Girls who grow up without their dads are more likely to reach puberty earlier, a new study has found.
Premature puberty has been a hot topic recently, with factors including diet and obesity linked to the phenomenon in girls as young as 7.
The latest findings from the University of California, Berkeley's School of Public Health showed that girls without biological fathers at home tended to develop breasts and pubic hair earlier than those with dads around.
Interestingly, the research held up even after weight was considered -- but only for those in higher-income households.
"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," study lead author Julianna Deardorff, an assistant professor of maternal and child health at Berkeley, said in a statement. "While overweight and obesity alter the timing of girls' puberty, those factors don't explain all of the variance in pubertal timing."
Instead, she explained, the findings -- published Sept. 17 in the Journal of Adolescent Health -- indicate that conditions related to family and environment also have "an important effect" on the age at which girls hit puberty.
Researchers examined 444 girls ages 6 to 8, following them annually and using the first two years of analysis for the study. They looked at signs of puberty that occur before the first period, including breast and pubic hair development. The authors interviewed the girls' caregivers, asking who lived in the home and what their relationships were to the children.
About 80 of those studied had absent biological dads, a condition researchers found was linked to earlier development of breasts in girls in higher-income families -- households bringing in $50,000 or more annually. Early signs of pubic hair only appeared in girls in higher-income African American families.
The authors struggled to explain the findings, which surprised them.
One theory is that girls without fathers around may come from shaky family environments, which can push them into puberty sooner than their peers.
Another is that those who don't grow up with their dads are typically exposed to more men who aren't relatives, and the males' pheromones could influence puberty age. In this research, however, the presence of stepfathers and other unrelated adult males didn't have an impact on the findings.
It also wasn't clear why socioeconomic status seemed to play a role. Deardorff said low-income families may have more people to help care for the child. And there are other, more controversial explanations, she added.
"Higher-income families without fathers are more likely to have a single mother who works long hours and is not as available for caregiving," she said. "Recent studies have suggested that weak maternal bonding is a risk factor for early puberty."
Little prior research has looked at how body mass index, ethnicity and income affect puberty onset. Last month, a study emerged finding that some girls showed the first signs of puberty when they were only 7 years old.