Answer:
The age at which menstruation begins has been declining in developing and industrialized countries over the past 100 years.
Explanation:
The average age at onset of menstrual periods varies between 12 and 13 years in industrialized countries, typically 2 to 2.5 years after the onset of breast development. Menarke is expected in most about a year in one direction or another from the average; for example, with the US average of 12.43 years, menstrual periods have only begun at 10% at 11.11, but already at 90% at 13.75. By the age of 15, the share will reach 98%.
In the 1860s, the average age at onset of menstruation in current industrialized countries was 16.5 years, after which it gradually declined. Early development has been found to continue beyond the 1960s. Nutrition appears to play a key role in the timing of menarche, as nutritionally scarce times have been reflected in past centuries as the onset of menstruation increases. In developing countries, menarche, like other forms of puberty maturation and growth, may be delayed compared to industrialized countries.
