It has been apparent for many years that the age at which girls reach puberty has been declining. For example, in 1920 girls reached puberty at 14.6 years, in 1950 at 13.1, and 2010 at 10.5, according to a report by Medical News Today on a new study published in the Journal of Clinical Endocrinology and Metabolism.
For the last decade or so, many theories have been put forth to account for these changes. It s pretty widely accepted that the earlier decrease in pubertal age was related to improvements in general nutrition. However, other, later theories included blaming environmental chemicals and individual foods, such as milk and other dairy products. In fact, in 2000, ACSH s Dr. Ruth Kava was quoted in the NY Sunday Times magazine refuting this latter theory. Indeed, she stated, what is much more likely is that the increasing prevalence of childhood obesity is somehow linked to the earlier onset of puberty in girls. And the recent publication in the Journal of Clinical Endocrinology and Metabolism gives some insight into how this link could operate.
Dr. Jonathan Pinkney of the Plymouth University Peninsula schools of Medicine and Dentistry in the UK and colleagues followed 347 healthy children from ages 5 to 15 years. Every year they assessed the children s BMI, sexual development, overweight and obesity status as well as various hormone and metabolite levels.
In particular, they found that levels of one protein, sex-hormone binding globulin (SHBG), was inversely associated with a girl s reaching puberty. SHBG binds to the sex hormones androgen and estrogen in both boys and girls. SHGB levels are initially high in childhood but decline significantly before puberty, in essence 'allowing' puberty to happen.
So it was not surprising that the SHBG levels were high in 5 year-olds, but decreased as they approached puberty. Most significantly, this decrease occurred earlier in girls who were overweight or obese, as did puberty. The authors also found that a number of hormonal changes were associated with obesity in children, and suggested that these might in some way affect the timing of the decline in SHBG levels and thus the onset of puberty.
In the Medical News Today article, Dr Pinkney was quoted: "These findings have significant implications for children's development and public health around the world. Reduction in the age of puberty, as a result of early weight gain, expedites physical and psychosocial development at a younger age, and this potentially means an earlier ability to reproduce as well as poorer long term adult health. The observed effects on puberty are another reason to take action against childhood obesity. "