Posted Sept 13, 2012
Girls today may be reaching puberty as much as four years earlier than generations before them because their diets are higher in calories, research from the University of Wisconsin-Madison suggests.
The findings — the first in primates to document a connection between diet and body growth and earlier puberty — appear in the journal Endocrinology.
The study does not suggest girls weigh significantly more when they reach puberty. Rather, they hit a weight associated with the start of puberty at an earlier age, said Ei Terasawa, a professor of pediatrics in the School of Medicine and Public Health who has studied puberty in rhesus macaques since the 1970s at the Wisconsin National Primate Research Center at UW.
Rhesus monkeys are studied by biomedical researchers because they are genetically and physiologically similar to humans.
The monkeys in the UW study reached puberty six months to a year earlier than a control group of monkeys the same age that consumed 33% fewer calories. The faster-maturing monkeys were not obese, but their bones and muscles grew faster and larger, said Joe Kurian, an assistant scientist at the center. The faster-maturing monkeys all had consistently higher total body fat and upper abdominal skin folds.
Researchers noted no significant difference in activity levels between the two groups of monkeys, so they suspect the high-calorie-diet animals had an excess energy balance.
The study involved only eight monkeys — four that were fed the high-calorie diet and four fed a controlled diet. But the findings were consistently dramatic, the researchers said.
Environmental pollutants, eating habits, lack of exercise and genetic traits all have been raised as possible causes of earlier onset of puberty in girls.
The new research about earlier puberty onset reinforces why children’s eating behaviors should be balanced with activity. Avoiding early weight gain also reduces the risk of adulthood diseases such as type 2 diabetes, cancer and heart disease.
Early puberty has emotional implications for girls, as well. A younger girl’s brain isn’t developed enough to handle the intense emotions brought on by puberty, Terasawa said.
“This can be very traumatic physically and psychologically to a young girl who is already showing signs of being a woman at age 8, rather than age 12,” she said.
Puberty is a complex topic not only from a physiologic standpoint, but also a psychological perspective, said Sadhana Dharmapuri, an adolescent medicine specialist at Children’s Hospital of Wisconsin and assistant professor of adolescent medicine at the Medical College of Wisconsin.
The UW study offers insight into the physiologic aspects of early puberty, she said. It’s interesting, Dharmapuri said, that the researchers were able to control environmental, genetic and chemical exposure factors.
“However there is much research that needs to be done in order to account for these other factors and the influence of higher caloric diets that children and adolescents are exposed to,” Dharmapuri said. “More importantly, it is necessary to understand the psychological impact of early pubertal development on children and how we can educate and support them emotionally through these changes.
“This study provides a step in that direction, emphasizing the importance of educating parents and children about what a healthy diet is and how it is important to their overall health and development now, not just 20 years down the road. This study reinforces the need for developing interventions that promote healthy life choices at a young age.”
Researchers in the Madison study noted the faster-maturing monkeys had elevated levels of two hormones leading to puberty onset, which liberates other hormones that trigger changes in the brain while the brain is still maturing in ways such as development of judgment.
A surge of puberty-induced hormones may trigger emotions more quickly, or with greater intensity, causing a girl to become more aggressive or sexually active earlier.
The invasion of hormones also likely structures or permanently programs behavioral dispositions, Kurian said.
“If this happens early, when the brain is still immature, those behaviors may be exaggerated or eliminated. Think sexual behaviors, aggressive behaviors, coping abilities.”
That’s an area of research that still needs more study, he said.
Eating a high-calorie diet also could change the chemical structure of genes, which could be passed on to future generations, said Kurian, making them more prone to earlier onset puberty, too — yet another area for additional research.
Researchers at the UW primate research center began studying the possible diet connection to earlier onset puberty when Terasawa noticed from records kept over the past 30 years that colony females were growing up faster and seemed to reach menstruation at an earlier age.
Before 1995, the monkeys were fed supplemental fruits and/or fresh vegetables three to five times per week. Since 1995, they have been fed daily fresh fruits. Higher-sugar treats such as fruit roll-ups, Fruit Loops cereal, marshmallows and yogurt were added in 2002 for foraging activities and training.
©2012 the Milwaukee Journal Sentinel