Italy noticed it first. It was the first country to lock down during the COVID-19 pandemic, and later in 2020, researchers at Florence’s Anna Meyer Children’s University Hospital were the first to point out a puzzling trend: More young girls than ever had been showing up to the hospital with clear signs of early-onset puberty.
The cases weren’t unique, but their frequency was. Since early-onset—or “precocious”—puberty first gained widespread clinical attention in the 1990s, it’s become steadily more common worldwide. Defined as the appearance of secondary sex characteristics such as breasts, pubic hair, and vocal changes or other signs of biological maturity in girls 8 or younger and boys 9 or younger, precocious puberty has been difficult for researchers to attribute to a single cause or mechanism. But a mysterious, pandemic-generated spike in cases—in Italy and beyond—has provided experts with a new opportunity to revisit their dominant theories in hopes of an answer. Case studies have now rolled in from clinics around the world, many of whom saw at least a two- or three-fold increase in precocious puberty diagnoses after March 2020. In China’s Henan Province, for example, doctors at 22 facilities saw five times more cases in 2020 than they did in 2018.
More recently, documentation has turned to inquiry.
There’s no conclusive answer about what causes premature development, though research shows that the constellation of factors at play includes stress and trauma, as well as lifestyle habits like poor diets and lack of exercise that are tied to weight gain in children. In many countries, pandemic measures saddled children with this exact package of pressures. It’s no wonder that precocious puberty rates soared.
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The Burden of Early Puberty
Precocious puberty is most often diagnosed in girls, simply because “puberty in girls is more visible,” says Sena Orsdemir, a pediatric endocrinologist at the Loma Linda University Children's Hospital, who authored a 2019 paper reviewing treatment options for precocious puberty. Growing breasts, for many girls, is a public experience, and in spaces like the American school system, developing early can mean a minefield of unwanted attention. Then there’s the distress of watching their bodies evolve, which can be jarring even for those old enough to have received proper context and education. “First and second graders, they’re not mature enough to handle this type of body change,” says Orsdemir. “That is a big stress for a young girl.” Perhaps as a result, early puberty has been linked to mood disorders and some behavioral issues. Aside from the psychological repercussions, precocious puberty can also put children at risk years later for diabetes, cardiovascular disease, and certain reproductive cancers. When signs show up early, often around age 6 or before, it can be treated with hormonal puberty blockers.
Though some cases are easily traceable to genetic or anomalous causes,like an ovarian tumor setting off hormone production, precocious puberty has most often been linked to obesity. Decades of research have found that childhood body weight (often classified by body mass indexBodyMI) is a strong predictor of menarche, or the onset of menstruation, in particular. The mechanism is often assumed to be hormones such as leptin, which grows more concentrated during puberty but is also produced by fatty tissue. A study published in 2012 found that BMI data was able to account for 40% of the variation in when girls began their periods. Early menarche is also associated with lower birth weight, as well as rapid childhood weight gain, supporting the theory that the physiology of body composition could govern the mechanism that kicks off puberty. Childhood obesity is a growing problem worldwide, which could help explain why precocious puberty has also remained on the rise internationally.
In her clinic, Orsdemir says parents sometimes ask about another possible cause: whether chemicals in our food, environment, and everyday items are affecting the production and expression of hormones in the body. But although they might play a role, many studies have tried and failed to identify any meaningful connection between specific substances and chemical classes and the early arrival of puberty. Other exposures, too, have been suggested to make an impact—inconclusive research has explored a potential link between electromagnetic fields emitted by everyday devices and altered endocrine function. “My families bring different herbal products, they bring different vitamins,” says Orsdemir. “They ask about different foods, different diets, and I tell them I don't have an answer because I don't have any evidence.” Instead, she reinforces the importance of proper nutrition for healthy child development.
The connection between stress and puberty
Still, none of this sufficiently explains the explosion in precocious puberty during COVID-19, and the newest wave of research has instead zeroed in on stress as a key driver. Stress was linked to early puberty before the pandemic, though there’s little evidence it’s a clear cause. Childhood sexual abuse is associated with the appearance of secondary sex characteristics as much as a year earlier in girls, as are a number of other environmental factors that are easily tied to stress, such as parental absence and race-related weathering.
In 2020, researchers saw cases skyrocket while locked down kids faced the stresses of a lifetime, leading to renewed interest in uncovering the specific mechanisms of action behind these stress factors. “We know from recent data that the psychosocial burden before and after the pandemic is increasing dramatically,” says Mohamad Maghnie, head of the pediatric clinic at the Giannina Gaslini Institute at the University of Genoa in Italy. When he saw the spike of precocious puberty in young girls at his clinic in 2020, he says, “my first thought was focused on lifestyle changes related to social isolation.” In his latest study, published in the Journal of the Endocrine Society on August 3, Maghnie and his team identify lifestyle changes as contributing factors that many children faced during the pandemic, such as poor eating habits, decreased movement, impaired sleep, and excess screen time. Their study, which looks at data from more than 100 girls suspected to be in precocious puberty from January 2016 to June 2021, found that of the patients seen during the first 15 months of the pandemic, nearly 90% had stopped all physical activity.
Because many of these lifestyle changes are also linked to obesity in children, it’s difficult to tell whether they contribute to the onset of puberty by altering BMI, stress levels, or both, but the pandemic provided an ideal experimental setup for endocrinologists to examine it. The key, Maghnie believes, will be to compare data “from different countries who underwent different models of ‘lockdown’ and protections,” which could help highlight the effects of certain stressors or lifestyle changes more than others. It’s also possible, Maghnie and his co-authors write, that the pandemic simply meant that parents spotted signs of precocious puberty earlier due to being confined with their children.
Researchers aren’t sure yet whether or not the increased rate of precocious puberty has continued, now years after lockdown, but anecdotal evidence from clinics suggests it has. Orsdemir believes that this is because people, including children, have not returned to their pre-pandemic habits. “This is becoming normal now,” she says. “In the long term, the biggest impact will be psychosocial for sure.”
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