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Growing up is hard to do: Chemical exposure and teenagers

This is the last article of a five-part series about chemical exposure in pregnancy and childhood. For more context, start here.


A global trend is emerging in teenagers that’s both cause for concern and piquing the interest of researchers: they’re going through puberty at a younger age, especially girls.

The timing of puberty in Canadian teens is one area study being conducted by researchers from the Maternal-Infant Research on Environmental Chemicals (MIREC) as they seek to understand how environmental and lifestyle factors play a role in puberty.

MIREC is an ambitious, multi-year study of environmental chemicals and their possible health effects on mothers and their children, starting during pregnancy and throughout childhood development, from infancy to adolescence.

Adolescence is a crossroads between childhood and adulthood. As children go through puberty, their bodies change and develop. The MIREC research project seeks to better understand how exposure to chemicals can impact the health of growing adolescents.

Mainly, the researchers want to determine whether prenatal exposure to elevated levels of various environmental chemicals, could impact puberty, metabolism and growth.

Puberty happens at different age for each person, and researchers are trying to find out the determining factors for its onset.

Puberty happens at different age for each person, and researchers are trying to find out the determining factors for its onset.

The age range for normal puberty can vary based on several genetic and environmental factors, but it’s usually between 9 and 11 years old for girls and 10 to 12 years old for boys. Usually by 16 or 17 years old, puberty is over. However, if puberty starts before the age of 8 years old for girls or 9 years old for boys, it is considered early.

“We are looking at timing and progression of puberty,” says Dr. Jillian Ashley-Martin, Research Scientist and Co-Principal Investigator of MIREC. “We want to know why girls are going into puberty at an earlier age than before. Does exposure to chemicals have an impact on when puberty starts and how long it takes to be completed?”

Early puberty can have long-term consequences on children. For example, they could be shorter than average, have behaviour issues, feel stressed, or self-conscious about their bodies.

“The average age of puberty is dropping worldwide, mostly in girls. The increase in body mass index (BMI) does not fully explain this trend,” says Mandy Fisher, Senior Epidemiologist at Health Canada.

Beyond the differences between boys and girls, researchers are now considering gender as well, rather than just focusing on biological sex, in order to understand the effects of chemicals on different groups of people.

To try to find out what is going on, MIREC researchers have been looking at the impact of chemical exposure during pregnancy, later in life.

“A lot of the chemicals that we are examining are endocrine-disrupting, meaning that they mimic or interfere with the body’s hormones,” explains Fisher. “Mainly, we want to determine whether prenatal exposure to elevated levels of various environmental chemicals could impact puberty, metabolism and growth.”

Physical activity

The MIREC team also wanted to know how active teenagers really are. They asked participants to wear an accelerometer, which is a sensitive instrument that measures their level of physical activity.

They get 43,000 observations each week for each teenager from this equipment and can combine all the results to get a good sense of how active they really are.

Researchers also ask participants about their typical activity level and combine that information with the data from the accelerometer. They will repeat these measurements at each stage of puberty, and will be able to see how things evolve.

“Boys who enter puberty earlier are usually better at team sports,” says Dr. Michael Borghese, Epidemiologist at Health Canada. “Does early puberty encourage them to be more physically active? Does the fact that they are physically active earlier on make them better at sports?”

Researchers will also be able to look at how physical activity might affect the levels of some chemicals. “So physical activity might be a modifiable factor in preventing the health effects of some chemicals,” says Dr. Borghese. “We are hoping to find out.”

Although researchers aren’t specifically studying the impact of COVID on teenagers through MIREC, they are considering how it might have impacted stress levels, as well as physical activity and screen time.

Researchers would also like to examine the link between diabetes and physical activity. They are looking at how both chemical and behavioural factors can have a cumulative impact on a person.

“It’s possible that early life chemical exposure might make someone more susceptible to the effects of low physical activity, which might make them more susceptible to diabetes later on,” explains Dr. Borghese.

Next steps

The MIREC researchers have been studying this group of adolescents since they were in utero and aim to keep following them as they age.

As the MIREC cohort is only just reaching puberty, researchers still have lots of exciting work ahead of them.

Over the next few years, they are hoping to find out whether chemicals to which children were exposed in the womb can still have an impact many years later.

For example, they are looking to find out whether exposure to metals such as lead and arsenic can have an impact on blood pressure. They also want to know whether a class of chemicals called perfluoroalkyl substances (PFAS) can alter puberty.

Stay tuned to find out more!


The MIREC research is a key part of the Chemicals Management Plan. This plan seeks to reduce the risks posed by chemicals to Canadians and their environment by assessing chemicals used in Canada and by taking action on chemicals found to be harmful to human health and/or the environment.

Research like this provides information to decision-makers and can help guide their actions to change the future.

Find out more:

Maternal-Infant Research on Environmental Chemicals (MIREC) Research Platform

MIREC Canada



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