First five years of a child’s life provide a critical window of opportunity for preventing overweight and obesity, Dutch study suggests

The first five years of a child’s life may be key to preventing overweight and obesity in years to come, say the authors of new research being presented at year’s European Congress on Obesity (ECO 2025).

The study found that a child’s body mass index (BMI) at the age of six is a better predictor of their risk of overweight or obesity at age 18 than their BMI at other points in their childhood.

Every one-unit increase in BMI at age six more than doubled (2.35 times) a child’s odds of being overweight or obese at 18. (BMI was adjusted for age and sex.)

The study also found that if a child with a higher BMI reached a healthier weight before the age of six, they were no longer at a higher risk of living with overweight or obesity in their late teens.

However, if they returned to a healthier BMI when they were six or older, they were still at higher risk of overweight and obesity.

This suggests that the first five years of a child’s life provide a critical window of opportunity for preventing overweight and obesity in young adulthood, says Jasmin de Groot, of Erasmus MC, University Medical Center Rotterdam, Rotterdam, the Netherlands.

Ms de Groot and colleagues used data from an ongoing prospective cohort study¹ in Rotterdam, the Netherlands, to track the BMI trajectories of thousands of children in the Netherlands.

Weight at birth (adjusted for gestational age and sex) and BMI at age two, six, ten, 14 and 18 years was available for 3,528 participants, 52.9% of which were female.

A child’s BMI generally increases with age. For this reason, the researchers used reductions at the rate in which BMI was increasing (i.e. a BMI that was growing more slowly) as an indicator of healthy growth – and of reaching a healthier weight – rather than a reduction in BMI.

Some 32.3%, 22.3%, 24.7% and 20.6% of the 3,528 children lived with overweight or obesity at the ages of 2, 6, 10 and 14 years, respectively.

Many of these children were still in the overweight or obese range at the age of 18. Of the children with overweight or obesity at the ages of 2, 6, 10 and 14 years, 32.5%, 53.9%, 57.2%, and 70.3%, respectively, still lived with overweight or obesity at 18 years.

A higher BMI at any point in childhood, regardless of earlier BMI, was associated with a higher chance of overweight or obesity at 18 years.

A high BMI at the age of six was particularly strongly associated with overweight and obesity at 18.

However, when the researchers split each age group into three groups based on their BMI, they found that if a child in the group with the highest BMI slowed down the growth of their BMI before the age of six, their odds of living with overweight or obesity at 18 were similar to those of a child with a stable, average BMI.

Reaching a healthier weight after the age of six did not have the same effect: the children with the highest BMIs were more likely to live with overweight or obesity aged 18 regardless of how their BMI changed from the age of six onwards.

The findings, say the researchers, emphasise the importance of monitoring BMI in early childhood.

Ms de Groot adds: “We need to understand how children grow and develop if we are to help future generations grow up healthier and give every child a chance at a happy, healthy life.

“Our research assists with this by showing that a child with overweight or obesity isn’t destined to live with overweight or obesity as a young adult – and that the first five years of a child’s life provide a fantastic opportunity to intervene and prevent them experiencing overweight and obesity in the years to come.”