In the past several decades, obesity in childhood has become increasingly common. This has been attributed to food being overall more accessible, the prevalence of high-calorie pre-packaged foods in the average diet, and more sedentary entertainment options such as television and video games. Video games and chips aren’t inherently bad, but the lack of balance in lifestyle has ultimately resulted in concerning health trends among youth.
A link has been observed between childhood obesity and precocious puberty, a condition that causes children to develop secondary sexual characteristics (such as facial/pubic hair and breasts) far earlier than their peers. Precocious puberty is over ten times more common in girls. This condition is defined by the development of breasts or pubic hair before 8 years in girls, and testicular or penile enlargement before the age of 9 in boys. Precocious puberty has long-term effects including a shorter final height of the child and it may result in behavioral or psychological disturbances.
Hormonal Bases of Obesity
As mentioned, the ultimate underlying cause of childhood obesity is a lack of balance. However, hormone disruption plays a significant role in perpetuating obesity. Leptin is a crucial hormone that indicates to our brain that we are full. Obese individuals have high levels of leptin, which may seem contradictory. After all, high levels of leptin should promote weight loss, right? For obese people, this isn't the case. People who struggle with obesity very often have a condition called leptin resistance - this means that their bodies do not respond to high levels of leptin, and therefore will not respond to fullness and the individual will keep eating.
Insulin is a hormone you may be familiar with, as it is often discussed in regard to diabetes. This hormone controls the amount of sugar in the blood. When gaining weight, there is generally substantially more insulin in the body due to higher sugar intake. When insulin rises, that indicates fullness to the brain, and tells our bodies we are ready to stop eating by increasing leptin - this is why we often will feel fuller if we have a carb-y food with a meal. Insulin resistance, also known as prediabetes, is a condition in which the body does not respond to heightened levels of insulin, so too much sugar remains in the blood. This also means that insulin is unable to aid in the regulation of leptin.
Hormonal Bases of Precocious Puberty
Metabolic comorbidities (coexisting conditions) are by far the dominant cause of precocious puberty. A certain amount of body fat is needed to maintain reproductive function - this is why underweight girls often report starting their period much later on. In the early 19th century when food was much scarcer, the average age of menarche (first period) was 17. We now know that 17 is very old for menarche since improved nutrition and hygiene in the 20th century caused the average menarche age to fall to around 13.
This age is falling further, however, due to the rise in childhood obesity. The start of puberty is rooted in hormonal changes, and the hormonal imbalances described above can trigger these changes earlier than what is considered healthy. Leptin and insulin all have direct effects on kisspeptin and Gonadotropin-releasing hormone (GnRH). These hormones are essential for the progression of puberty, and imbalances in the hormones responsible for digestion can result in the release of the hormones responsible for puberty occurring too early.
Kisspeptin is a hormone that promotes pubertal activation. It is very sensitive to metabolic activity, as increases in leptin are directly responsible for increases in kisspeptin. Since people with obesity tend to have higher levels of leptin, the release of kisspeptin would consequently begin earlier in obese children. Additionally, pediatric obesity is associated with a highly active KISS1 system, the system of hormones that includes kisspeptin and GnRH.
GnRH is a hormone that, as indicated by its name, is responsible for regulating the release of hormones known as gonadotropins. Gonadotropins include follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH are both responsible for ovulation and the production of sperm, and are therefore essential for fertility and the onset of puberty. Having high leptin levels directly results in increased kisspeptin and FSH. As discussed previously, obesity is associated with high levels of leptin. This forms the link between childhood obesity and precocious puberty.
Why is Precocious Puberty a Concern?
Precocious puberty has a variety of consequences. One of the more mild ones is shorter adult stature. Since puberty ends significantly earlier, that means that growth will also stop significantly earlier, resulting in a shorter final height. On a more serious level, precocious puberty often leads to a variety of psychological problems later in life, especially since adolescence is not a time in which one wants to stand out among their peers. Boys with precocious puberty have often been observed to have higher risks of anxiety, depression, and substance use. For girls, a very clear link had been drawn with precocious puberty and depression as well as eating, behavioral, and substance use disorders.
Precocious puberty can be prevented with a healthy lifestyle in childhood. Avoiding excess consumption of high fructose foods and encouraging exercise are both effective ways to prevent precocious puberty. Encouraging outdoor play is also important, as low vitamin D levels have been observed to help prevent precocious puberty. When prevention fails, GnRH analog treatment is used to control the levels of GnRH to delay puberty to the appropriate time. Different studies have provided a variety of different results in terms of final adult height, so it is unclear if adult height is preserved through GnRHA treatment. Adults who receive GnRHA treatment often have a normal BMI and body composition despite childhood obesity. However, insulin resistance is often still observed in patients long after GnRH analog treatment, despite the normalized BMI. Prevention is still the ideal method, as the psychological and height-related impacts of early puberty can persist despite treatment.
Further reading:
Assessed and Endorsed by the MedReport Medical Review Board