The timing of puberty: is it changing? Does it matter?

Whether the secular trend of a decreasing age of puberty has continued over the past 50 years remains controversial. Data that had been classically used to address this issue are reviewed and large epidemiologic studies, which had not previously been included, are now considered to challenge the conclusions of prior debates of this topic. The effect and timing of excessive weight gain are discussed in detail and recent observations about the opposing effects of obesity on the pubertal timing of girls versus boys are considered. The second half of the review examines both the causes and the long-term health consequences of early puberty, touching on the possible effect of stress and endocrine-disrupting chemicals along with the risks of reproductive cancers, metabolic syndrome, and psychosocial consequences during adolescence and beyond.