More than ten years ago, a study found American girls were beginning puberty as early as age 7. A new study in the journal Pediatrics suggests the average age at which puberty begins may still be falling for white and Latina girls: almost 15 per cent of Latina girls have reached a stage of breast development marking the onset of puberty by age 7, as have more than 10 per cent of white girls and 25 per cent of African American girls. These percentages are higher than those in the landmark 1997 study, which reported that girls were beginning puberty at earlier ages than in the mid-20th century. Compared with the 1997 data, the age at which puberty begins did not fall for African American girls, although they still mature at younger ages than white or Latina girls. Causes for the diminishing age of puberty include an increase in average body weight among children, which is thought to increase the blood levels of estrogens that promote breast development; diets that are increasingly high in sugar and fat, along with declining physical activity and exposure to endocrine disrupters; and the increased presence of environmental chemicals that affect hormones.