What Is the Definition of Secular Trend?

How does it relate to menarche and puberty?

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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.

Defining the 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 have occurred about four months earlier with each passing decade.

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 higher 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

Early onset puberty has been linked to a variety of causes--including obesity, to the addition of hormones to meats and the chemicals in hair and beauty products.

Psychosocial causes, such as the absence of a father or experiencing a traumatic event, have also been held responsible for the decrease in secular trend.

 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 percent of children were obese.

Today, close to 20 percent of children are. 

Why does obesity cause puberty to occur earlier? The answer is simple: Fat cells produce estrogen. Because estrogen kicks puberty into gear, overweight and obese girls are more likely to undergo puberty at younger ages.

Even girls at normal weights are experiencing puberty earlier, however. Researchers have put the blame on chemicals known as endocrine disruptors. 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 of the Secular Trend

The secular trend has important biological and psychological consequences. Early onset 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.

Sources:
Biro, Frank M., et al. (2010). Pubertal assessment method and baseline characteristics in a mixed longitudinal study of girls. Pediatrics. Retrieved August 13, 2010:

Walvoord, Emily C. The timing of puberty: Is it changing? Does it matter? Journal of Adolescent Health. 2010. 1-7.

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