The Secular Trend, Menarche, and Puberty

Pediatrician talking with patient and mother in office
There are a number of reasons why girls may experience puberty earlier than their peers. Hero Images/Getty Images

There are a lot of terms that relate to puberty, and you may know many of them. One of the terms many parents don't know is Secular Trend. What is the secular trend and why are there concerns about changes in this phenomenon as it relates to puberty in recent years? Get the definition of this trend and the external forces that influence it with this review.

Definition of Secular Trend

The secular trend refers to the average age of puberty decreasing over time. Since the 1900s in the United States, puberty seems to be occurring earlier. Nutrition may play a role in why this occurs. The onset of puberty in Western nations such as the U.S., for example, is typically years earlier than it is in developing nations.

But in some cases, the age at which puberty occurs is highly abnormal, such as breast development occurring in seven-year-olds or preschool children, both of which have happened according to a 2015 report in Scientific American.

Scientists debate whether the secular trend is continuing to occur. Some say that the secular trend may have leveled off in the 1970s. There is evidence, however, that girls are currently experiencing earlier breast development and other signs of precocious puberty than in previous decades. Whether age of first period (menarche) is continuing to decrease remains debated.

Causes for Puberty Occurring Earlier

The precise reason isn't known, however it may be due to obesity, nutritional changes or possibly as the result of exposure to endocrine disruptors in the environment.

After the 1970s, the obesity rate in children not only began to grow but is now more than triple what it used to be. In 1980, for example, just 7% of children were obese, but by 2012, 18% of children are considered to be obese.

Why does obesity cause puberty to occur earlier? According to a study published in 2017, there are three possible reasons. Earlier onset of puberty may be due to insulin and insulin resistance, which is associated with higher levels of estrogen, inflammatory reactions that cause the body to produce more androgens, or increased levels of leptin that interact with hormonal levels.

Even girls at normal weights are experiencing puberty earlier, however. It's possible, that chemicals known as endocrine disruptors are involved, although more research is needed. Examples of such disruptors include bisphenol-A, which is found in plastics, as well as pesticides and polychlorinated biphenyls. They've all been known to have an estrogen-like effect on the body.

Much of the focus on early-onset puberty is on girls, but some studies indicate that boys are also starting puberty earlier. They appear to be beginning the physical maturation process as early as six months to two years earlier than they had a few decades ago.

Consequences 

The secular trend has important biological and psychological consequences that parents should know about. Early onset of puberty has been linked to cancer and other diseases.

Children who experience puberty at early ages may be more likely to be depressed because they may physically show signs of maturity while not yet being emotionally mature. Adults and peers, however, may treat them as if they are older than they actually are. Moreover, children who experience puberty at an early age may be more likely to abuse drugs and alcohol or have sex at young ages.

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Article Sources

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  4. Li W, Liu Q, Deng X, Chen Y, Liu S, Story M. Association between Obesity and Puberty Timing: A Systematic Review and Meta-AnalysisInt J Environ Res Public Health. 2017;14(10):1266. doi:10.3390/ijerph14101266

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