Influence of obesity on timing of puberty.

Timing of normal pubertal maturation has received increased attention over the past several years. Age of menarche showed a dramatic decrease in the first half of the 20th century in Western nations; since 1960, the decrease in age of menarche has slowed and, in some societies, has actually increased. More recently, age of onset of pubertal maturation appears to have decreased, especially in girls. Multiple studies have demonstrated that childhood levels of obesity and ponderosity are associated with earlier menarche in girls. Earlier maturation in boys, however, is associated with lower adiposity and ponderosity. Secular changes in the United States as well as around the world have noted increases in prevalence as well as extent of overweight. Factors contributing to these changes include increases in calories and fast food consumption, decreases in physical activity, and increases in television viewing. There appear to have been selective advantages to lower metabolic rate (the 'thrifty' gene hypothesis), and earlier maturation. However, changes in caloric consumption, caloric density and physical activity, combined with greater lifespan, may allow expression of the adverse consequences of these adaptations, such as the metabolic syndrome or cancers.