Lessons from large population studies on timing and tempo of puberty (secular trends and relation to body size): the European trend.

Ever since the publication of the first textbook on human growth by Johann Augustin Stoeller in 1729, temporal changes (or secular trends) in growth and pubertal maturation have been observed throughout the world. Data covering the longest time span are often reported from European populations. For example, in Norway and Denmark the age at menarche has fallen rapidly since the 19th century, by up to 12 months per decade. These changes have broadly paralleled increases in adult height in most European countries over the last century, with rates of around 10-30mm per decade. These secular trends are influenced by background ethnic, geographical and socio-economic factors, and clearly nutritional changes have an important role as reflected by positive correlations between age at puberty onset or age at menarche and childhood body size. Changes in height, pubertal maturation, and childhood body size have all also been related to rate of weight gain in infancy, and there is growing evidence to suggest that this early postnatal period may represent an early window of susceptibility to long-term 'programming' of various outcomes in humans. There is debate as to whether the secular trends in pubertal maturation are continuing or have reached their limit. Even where temporal changes are overall clearly significant, they are most marked in the more nutritionally deprived sub-groups. Whether over-nutrition and increasing childhood obesity will continue to lead earlier puberty is uncertain. The confirmation of an estimated advance in the age at menarche of 6-12 months per 100 years will require a long-term perspective on behalf of current investigators, and new consideration of methodological approaches in an age of increasing recognition of children's rights for privacy.