The role of fat in early puberty
Question: There is ample evidence that children are, on average, becoming chunkier. There is also ample evidence that girls are achieving puberty earlier than they used to. Is there a connection?
Background: Beginning in the early 1970s, Rose Frisch, an outstanding Harvard epidemiologist, observed that heavier girls matured earlier. There is a point before puberty at which girls usually begin to load on fat; Frisch hypothesized that this normal accumulation had to reach a critical point before menarche. The idea that good fat stores are a precondition for reproduction is biologically plausible: It takes about 50,000 calories above a woman's baseline metabolic needs to support a growing fetus over the course of a pregnancy. If women could become pregnant before they had the capacity to meet this need, it could be dangerous to the pregnancy. But does fat accumulation trigger menarche, or is it the other way around, with the changes of puberty causing the accumulation of fat? It has been hard to definitively answer this question.
New study: Now, some new research by Joyce Lee and Julie Lumeng of the University of Michigan and their colleagues offers some clarity. They studied about 350 girls of diverse socioeconomic and geographic origins, all born in 1991. The girls' heaviness was estimated at 3 years of age and again at 4½ by calculating their body mass index percentile, an indirect measure of obesity, normal weight, or thinness. The girls were then tracked over time for evidence of the onset of puberty. As was expected from previous research, other factors like race, mother's age of puberty onset, and mother's education played a role in predicting when a girl would reach puberty. But none of these factors were nearly as important at predicting early puberty as a history of being overweight at age 3 or 4.
Next question: To my mind, this careful study establishes that the excess weight commonly seen in girls who reach puberty early is present long before the first signs of that development. What's still unknown is whether the weight itself sets off early puberty (indeed, we still have little understanding of the bodily events that trigger puberty) or whether some other event in the body leads to both the excess pounds in early childhood and to early maturation. Perhaps the connection has to do with leptin, a hormone manufactured by body fat. Leptin suppresses food intake by decreasing appetite, is known to bind to ovarian tissue, and has been used to restore menstruation to women whose periods have ceased because they are too thin.
Conclusion: Whatever the mechanism, the relationship between excess weight in childhood and early sexual maturation is worrisome. The increasing rate of childhood obesity may well lead to a general increase in some of the developmental problems we have come to associate with early puberty—including earlier initiation of alcohol use, earlier sexual debut (with its risk of early pregnancy and exposure to sexually transmitted diseases), and perhaps an increase in social and psychological problems. The stakes in the control of childhood obesity may turn out to be even higher than we thought.
Is cold medicine really unsafe for kids?
Question: Last week, the New York Times ran a front-page story about a CDC study that argued that over-the-counter cold remedies for children are probably useless and could be dangerous. It is easy for me to agree that most of those medicines don't do much—I've never seen any evidence in my patients that they're at all helpful, and here's my take on cough medicine. But dangerous? I'm not so sure.
New study: The CDC report, on three infant deaths in 2005 associated with the use of over-the-counter cold medications, is troublesome—and not what I would like to see as the basis for serious policy decisions. The authors searched the published literature and polled coroners and medical examiners in the United States and came up with only three infant deaths as a result of the use of cold medicine—all occurring in children under 6 months of age and all with sky-high blood levels of the active ingredient in over-the-counter remedies, pseudoephedrine. This suggests massive overtreatment by parents. Two of the three infants had pneumonia when they died, and the remaining infant had a multiplicity of risk factors that complicates understanding of the cause of death.