New Kaiser Permanente study supports previous research suggesting link between early life family structure and onset of puberty
Girls who did not live in a 2-parent household from birth to age 2 were significantly more likely to start puberty earlier than girls who had both parents in their home, new Kaiser Permanente research shows.
The study, published October 28 in the journal BMC Pediatrics, adds to previous research showing a connection between whether one or both parents live in a household and timing of onset of puberty.
“This study is a part of a series of studies we are conducting looking at early life risk factors that could contribute to early puberty,” said the study’s senior author Ai Kubo, MPH, PhD, a research scientist and epidemiologist at the Kaiser Permanente Northern California Division of Research. “If we can identify these risk factors, we can then talk about what we can do to reduce the risks of early puberty. This is important because early puberty is known to increase risk for various conditions, including cancer.”
It is widely recognized that girls in the U.S. are reaching puberty at an earlier age than they did decades ago. A recent meta-analysis found the average age of onset of puberty decreased by about 3 months per decade from 1977 to 2013.
Early puberty concerns health care providers, researchers, and parents because it has been shown to increase a girl’s short- and long-term health risks. For example, studies have found that early puberty is associated with an increased risk for mental and emotional problems such as depression, eating disorders, and substance use as well as risky sexual activities and underage pregnancy. As adults, girls who started puberty early are at increased risk for breast and uterine cancer; this is believed to be due to their longer duration of exposure to the female hormones that increase cancer risk.
The new study included 26,044 racially and ethnically diverse girls born at a Kaiser Permanente Northern California (KPNC) medical facility between 2003 and 2010. The researchers used the girls’ electronic health records to learn whether a girl lived with both parents from birth to age 6 (the child’s parent or caregiver is asked this question at about half of all KPNC well baby/child visits), the stage of her pubertal development, which pediatricians assess starting age 6, and whether the girl had begun menstruating.
Their analyses of these data found girls who did not live with both parents from birth to age 2 were 29% more likely to have earlier onset of breast development and 38% more likely to have begun menstruating before age 12, compared to the girls who lived with both parents. Girls who did not live with both parents from age 2 to age 6 were 13% more likely to have early breast development and 18% more likely to have begun menstruating before age 12.
If we can learn how family stress affects girls and puberty, we can intervene in ways that could lower their risk for cancer later.”
— Ai Kubo
Previous studies have found racial and ethnic differences in girls’ age at the onset of puberty. In the new study, the association between not living with both parents and early puberty was strongest among Black girls. A 2013 study by some of Kubo’s co-authors that looked at other aspects of puberty found the median age of breast development was 8.8 in Black girls, 9.3 in Hispanic and Latinx girls, and 9.7 in white girls.
Studies also have found that girls who are not raised with a biological father are more likely to start puberty early. Why the presence or absence of a biological father would influence the onset of a girl’s puberty isn’t well understood, but multiple hypotheses exist. One theory suggests that psychosocial circumstances, such as living with only one parent, which may lead to less stability and more stress, can trigger “a biological response that has the girl develop more quickly so she can reproduce faster to preserve her genes,” said Kubo. “A second theory, based on pheromones, suggests that when the biological father is in the home, he secretes hormones that delay his daughter’s development.” This is believed to be an evolutionary development to prevent inbreeding.
In the new study, the researchers could not determine which parent was in the home. “We don’t know if single-parenthood was by choice or due to divorce, or if other people lived in the household, like a grandparent, or boyfriend or if there were older siblings,” said Kubo. “All of these factors can affect the stress levels of the household and having these details could help understand what might protect the girls from having earlier puberty.”
Kubo intends to continue to study ways stress affects human health. “In this study, family intactness early in life is a surrogate for exposure to stress,” she said. “If we can learn how family stress affects girls and puberty, we can intervene in ways that could lower their risk for cancer later.”
This study was funded by the National Institutes of Health.
Co-authors include Sara Aghaee, MPH, Charles P. Quesenberry, PhD, and Lawrence H. Kushi, ScD, of the Kaiser Permanente Division of Research; Julianna Deardorff, PhD, of the University of California, Berkeley; and Louise C. Greenspan, MD, pediatric endocrinologist, The Permanente Medical Group.
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About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 450 epidemiological and health services research projects. For more information, visit divisionofresearch.kaiserpermanente.org or follow us @KPDOR.