A trend toward earlier menstruation of children is confirmed by the decline in the age at which girls 1st menstruate and increases in children's height and weight. Reports documenting a change in children's size between 1880 and 1960 are available from several European countries, the US, Canada, Japan, Hong Kong, New Zealand, and Australia. The data suggest that, beginning in 1900, children aged 5-7 years who lived under average economic conditions increased in height between 1/2-3/4 inch/decade. The height increase for those 10-14 years of age has been 1-1 1/2 inch/decade. Children 5 years of age in 1965 were 2 inches taller than their counterparts 50 years earlier, 9 year olds were 3 inches taller, and 11 year olds were almost 4 inches taller. This trend appears to be levelling off in the US, indicating that the best-off children have approached the maximum rate of maturation. An even more dramatic trend has been noted for average age at menarche. Menarche has been experienced progressively earlier, to the extent that puberty occurs 2 1/2-3 1/2 years earlier than it did 100 years ago. Moreover, there is no indication that the current level represents the earliest possible age. Nutrition is regarded as the environmental factor most responsible for earlier puberty and large size. Support for this hypothesis is provided by data from England and Poland showing a stronger trend toward earlier maturation among poor children whose lives have been more dramatically improved by modernization. A consistent relationship has also been noted between age at menarche and family size. The larger the number of children, the later the menarche and the less the height and weight at all ages. The sibling-number effect may be expressed through malnourishment or a greater incidence of chronic diseases. It is concluded that although the trend toward larger size and earlier maturation has been firmly established, its causes remain to be investigated.
