Numerous factors control puberty - nutrition, gender, family genetics, environmental factors, race, and hormones. Obesity is affected by these factors also. A trend in both earlier puberty and childhood obesity has occurred over the years.
Are the two related? What do we know?
Frequently, obese children tend to mature earlier than their leaner counterparts. Children who are obese tend to have higher hormone levels of leptin, insulin, and sex hormones than those not overweight. Leptin is a hormone that regulates appetite, as does insulin; these hormones are higher with obesity. This earlier trend toward puberty is seen primarily in obese girls and less frequently in boys.
What are the usual ages for puberty?
Puberty can occur in girls starting at eight and in boys at nine. There is a range of ages for pubertal onset, usually dependent on the family history. Girls often follow their mother’s, aunt's, and sister's patterns.
Girls typically enter puberty from ages 8-14 and boys from 9-15. The hallmark of puberty in girls is breast budding. Underarm body odor and pubic hair can occur before this, (what is called adrenarche), but breast budding marks the start of puberty.
Boys have a more subtle sign - enlargement of the testicles, which is not as noticeable a change as in girls.
Girls take about four years to complete their puberty and boys five years. Menses, or periods, do not usually start until 2-3 years after breast budding occurs. Parents would often panic when I mentioned their child was in puberty, thinking menstruation was right around the corner, then would relax once I let them know it was still at least a couple of years away.
Being overweight or underweight can affect when puberty starts in girls. We do not see this trend in boys. A young girl must have a certain minimum weight and amount of body fat for puberty and menstruation to occur. Underweight girls or those with anorexia have delayed puberty.
Overweight girls often enter puberty early or at the early end of the normal age range. They also tend to have an accelerated growth rate and accelerated maturity of their skeleton. These factors do not usually increase adult height due to an earlier and lessened growth spurt and the completion of their growth early due to the advanced skeletal maturity.
I frequently assessed a child’s skeletal age in practice by obtaining a bone age x-ray which is an x-ray of the left hand and wrist. Obese children tend to have an advanced bone age compared to non-overweight children. In other words, their bones are older than their age. This advancement can compromise their growing years. The bone age or skeletal maturity is likely related to: 1. increased insulin levels, which affect receptors at the growth plates, and 2. possibly increased estrogen levels, made in fat tissue, which also affects bone growth. Skeletal maturation or bone age tends to correlate with the timing of puberty.
Obese children tend to be taller and mature faster as a child, yet are not taller once an adult, since their growth is completed early due to advanced bone maturity. Some factors that lead to earlier puberty in obese children include an increase in multiple hormones, including leptin, insulin, and sex hormones (estrogen and androgens).
The good news is that despite girls trending toward an earlier age at puberty (breast development), the average age for starting periods has remained about the same.