Sexual development is more likely to occur earlier when a girl’s father doesn’t live in the home, but only in higher-income families, according to new study findings reported by a research team led by scientists from the University of California and Kaiser Permanente Northern California.
The overall aim of their ongoing study is to identify factors that contribute to the onset of puberty in young girls. The possible contributors to early sexual development that are under investigation include not only exposure to chemicals in the environment, but also dietary and even behavioral and social factors.
The study, called the Cohort study of Young Girls’ Nutrition, Environment and Transitions, or CYGNET, has enrolled 444 girls, aged six to eight, and will track their development, lifestyle factors and environmental exposures for at least 10 years. This latest finding, reported on Sept. 17 in the Journal of Adolescent Heath, is based on the analysis of the first two years of data.
The research is part of a broader program undertaken by a consortium called the Breast Cancer and the Environment Research Center (BCERC), which is funded primarily by the National Institutes of Health.
Consortium researchers last year helped bolster earlier scientific evidence indicating that girls now are undergoing sexual development sooner compared to girls in prior decades. Early sexual development – more specifically, early age of first menstruation – is associated with an increased risk for developing breast cancer later in life.
BCERC research findings also have bolstered evidence that girls who are overweight or obese are likely to develop sexually at an earlier age.
The link between family factors, including a father’s absence, and a girl’s sexual development also has been observed in previous epidemiological studies and in animal studies, according to the leading author of the report, Julianna Deardorff, PhD, an assistant professor of maternal and child health at UC Berkeley and an adjunct assistant professor of obstetrics and gynecology at UCSF.
However, Deardorff notes, the new study is the first to separate out the effect of a father’s absence from the influence of body mass index (BMI), confirming that the influence of having an absent father remains as an independent factor after taking a girl’s weight into account. Researchers had earlier speculated that the absence of a father might plausibly lead to a less stable home environment, or to less attention at home, which in turn might lead to stress-related overeating. However, BMI did not act as a causal mechanism.
“A strength of our study is in the ongoing monitoring of breast and pubic hair development in the clinic as it relates to other information we have been collecting related to social environment and behaviors,” Deardorff says.
The association between a father’s absence and early sexual development was only statistically significant in families earning $50,000 yearly or more.
Why would the absence of a father independently hasten a girl’s sexual development, and why would the effect only appear significant in higher-income families? There are several ideas that may be worth investigating further, according to Deardorff.
University of London researcher Jay Belsky, PhD, has proposed that mammals have evolved to mature and reproduce early in the absence of optimal parental protection. If parents cannot be present or attentive, individuals may be more likely to live long enough to pass on their genes if they form their own families early. The presence of a father may exert an influence through molecules called pheromones that signal via olfactory glands.
Deardorff notes that the effect of an absent father on girls’ sexual development might relate more directly to added pressure on single mothers to work and provide for their families, which increases the stress level in the home and potentially takes away from parent-child interaction.
The association with higher income may be due to mothers also being less available in these families due to increased work hours, Deardorff suggests. Girls in lower-income families might also be more likely to be closer to other relatives or to rely on alternative caregivers.
In addition, in related animal studies it has been observed that exposure to artificial light causes earlier sexual maturation. In higher-income families girls may be spending more time in front of computers or television screens, Deardorff suggests.
The causal pathway for the new results essentially remains unexplained, she adds. Deardorff is interested in learning whether the observed associations are more directly due to stress.
“Until now, we have not examined data related to other interesting family factors, such as maternal depression, other stressful events, and biological stress mechanisms,” she says.
Deardorff and her colleagues plan to investigate stress levels and girls’ responses to stress in another long-term study of young children.
Father Absence, Body Mass Index, and Pubertal Timing in Girls: Differential Effects by Family Income and Ethnicity
Julianna Deardorff, John P. Ekwaru, Lawrence H. Kushi, Bruce J. Ellis,
Louise C. Greenspan, Anousheh Mirabedi, Evelyn G. Landaverde, and
Robert A. Hiatt
Journal of Adolescent Health (September 17, 2010)
Flame Retardants, PCBs & Pesticides Found in Blood of Young Girls
UCSF Science Café, March 17, 2010
Community Forum Highlights Environmental Breast Cancer Risks
UCSF Science Café, November 20, 2009
Early Puberty and Early Exposure to Breast Cancer Risks: A Conversation with Robert Hiatt
UCSF Science Café, September 19, 2008
UCSF Magazine, April, 2004