Breastfeeding could help prevent early puberty in girls and boys, South Korean study finds

Girls and boys who were exclusively breastfed during their first four to six months showed a reduced risk of early puberty, according to a large new study from South Korea that Canadian doctors say could apply here.

The study, published in Monday's issue of JAMA Network Open, looked back at the diets and development of more than 300,000 children from 2007 to 2020, based on data from checkups at four to six months of age and before six years.

Worldwide, puberty has increasingly begun earlier in kids. Called "central precocious puberty," it's linked to an increased risk of health problems in adulthood, like heart disease, cancer and diabetes, as well as mental health issues like depression and anxiety.

The researchers believe that kids who are exclusively breastfed are less likely to develop childhood obesity, a major predisposing factor of early puberty. However, experts note that many mothers face challenges in breastfeeding, which they say should be addressed on a structural level.

"The take-home message should be, for parents or to-be parents, that breastfeeding has multiple beneficial health effects for their children," said Dr. Sonia Anand, associate vice-president of global health at McMaster University, who was not involved in the study. "And the second message is it is not always easy to do."

About 46 per cent of the babies in the South Korean study were exclusively breastfed, more than a third had formula and nearly 20 per cent had both.

"The idea is that breastfed kids are less likely to have extra weight and that's the mechanism whereby they're more protected from developing early puberty," said Dr. Kaberi Dasgupta, a professor of medicine and physician scientist at the McGill University Health Centre, who also was not involved in the study.

Boys who were fed just formula had a 16 per cent increased risk of early puberty compared with their peers who were only fed breast milk, the researchers found. For exclusively formula-fed girls, the association jumped to 60 per cent. For mixed-fed boys, it was 14 per cent higher, compared with 45 per cent for girls.

The researchers noted some caveats to their study. The participants self-reported how long they breastfed their children, for example. It also couldn't include genetic factors like maternal age of puberty.

The early part of life is a key time, as that's when a lot of disease risk is set, wrote doctors Lin Yang and Shengxu Li. Though they weren't involved in the study, they wrote an accompanying journal commentary.

"Disease starts early, so should its prevention," they said.

Dasgupta says there's no reason to think the findings would be different in Canada. Preventing early puberty can also help kids in other ways, she adds.

"The earlier your puberty, the shorter you may become," she said. "There's also the stigma around having early signs of being an adult when you're still a kid. Other kids may tease you."

Yang and the researchers say that instead of putting pressure on new moms, a society-wide approach is important. That includes stronger parental leave policies, workplace accommodations like a private space to breastfeed and lactation support services.

"I think policy support, raised awareness, as well as creating the environment for women to be able to [breastfeed] is very important," Yang told CBC News.

Sleep patterns, physical activity levels and screen time could also be increasing childhood obesity and early puberty rates, Yang and Li wrote in their commentary, as well as environmental pollutants like endocrine disruptors, though she acknowledged there isn't good data on that.

In Canada, about 91 per cent of parents start out breastfeeding. About 38 per cent of parents breastfed exclusively for at least six months, Statistics Canada reported in 2024. Of those who stopped before six months, reasons included not having enough breast milk, finding breastfeeding difficult and the child weaning themself off of it.

"I think the wrong takeaway and the wrong approach is to shame mothers who try to breastfeed but can't continue," Anand said.

Breastfeeding is one factor among many that can influence weight gain in kids. Lifestyle choices like limiting fast food and cooking with more vegetables and lean proteins can also help prevent childhood obesity, doctors say.

While the South Korean study doesn't prove that formula feeding causes early puberty, the researchers had a robust data set and the associations are plausible, she said.

Anand's own research demonstrated early breastfeeding and for at least six months was associated with lower levels of excess body fat in children at age three.

She says she'd like to see other large studies show similar findings to the South Korean to nail down cause and effect. Studies looking at how genes are tied to precocious puberty could also help, she said.