More Than Half of Children Projected to Be Obese By Age 35

Zachary J. Ward, MPH

A new growth-trajectory study published in the New England Journal of Medicine predicts that 57.3% of today’s children will be obese by the age of 35. Of that population, more than half are already obese.

Researchers from Harvard University, led by PhD candidate Zachary J. Ward, MPH, reported that early development of obesity as defined by body mass index (BMI) predicted adulthood obesity — especially in children who suffer from severe obesity.

As part of the Childhood Obesity Intervention Cost-Effective Study (CHOICES), the team analyzed 176,720 observations from 41,567 children and adults from 5 US-based data sets that contain individual height and weight measures.

Researchers then made a simulation model for growth trajectory prediction, based on the individual height and weight information. Childhood trajectories were based on growth curves set by the Centers for Disease Control and Prevention (CDC) after adjustment for secular trends in weight from National Health and Nutrition Examination Survey (NHANES) data from 1976 through 2014.

Trends were estimated for 4 BMI categories: underweight/normal weight, overweight, moderate obesity, and severe obesity.

Researchers predicted the risk of obesity at 35 years old through virtual populations of 1 million children, aged 19 years or younger, using statistical matching techniques that produced nationally representative, open populations beginning in 2016.

The conditional probability of obesity at 35 years old was estimated with BMI status at each childhood age, calculated with associated relative risks. Researchers also calculated the risk of future obesity at 5-year intervals for each BMI group, based on age and sex. The process was repeated with 1,000 independently generated populations.

Using current BMI and obesity trends, the researchers projected that 57.3% (95% uncertainty interval [UI], 55.2 to 60) of children between 2 and 19 years old will be obese at 35 years old.

The probability that obese children will remain so at 35 years old increased with age, from 74.9% (95% UI, 67.3 to 81.5) at 2 years old, to 88.2% (95% UI, 84.6 to 92.3) at 19 years old.

Adversely, the probability of children who were not obese becoming obese by the age of 35 decreased with age, from 57.8% (95% UI, 54.5 to 62.1) at 2 years old, to 44.4% (95% UI, 40.4 to 49.7) at 19 years old.

Though the results show a correlation between childhood and adulthood obesity, researchers reported that a majority of obese 35-year-olds were not obese as children. Childhood obesity had a specificity of 93.1% as an indicator of adult obesity, but also a low sensitivity of 29.3% on average.

That said, the population that continues to struggle with obesity from childhood into adulthood is at great risk of relevant diseases. Ward noted to MD Magazine that most obesity risk factors — heart disease, diabetes, and certain cancers — occur later in life.

Severe obesity late in childhood is almost a certain indication for adulthood obesity, according to the study. The probability of not being obese at 35 years old was set at 21% (95% UI, 7.3 to 47.3) in severely obese 2-year-olds; the probability drops to just 6.1% (95% UI, 2.1 to 9.9) in severely obese 19-year-olds.

Researchers wrote that severe obesity currently affects about 4.5 million children in the US.

Ward said results showing a probability of obesity in a majority of patients is “certainly alarming.”

“The sheer magnitude of the problem is alarming,” Ward said. “But it’s not surprising when looking at net weight gains in the past 40 years, which we did for this study.”

Ward was surprised at the persistence of obesity risk in younger ages, though. His previous perception was that obese children would be more likely to “grow out of it” as they aged.

“We didn’t model out underlying causes, but it seems excess weight in childhood is hard to phase out over the years,” Ward said.

The study was limited by assumptions and limitations underlying the growth prediction pattern, the main assumption being that simulated persons would have similar trajectories in height and weight over years. Researchers were also unable to examine excess weight in infants aged younger than 2 years due to available CDC data.

Ward said the research served as a “natural history” study in conjunction with CHOICES. With a projection map of childhood obesity now set, the study will move on to modeling and analyzing the impact of obesity intervention methods.

Isolated efforts in combating childhood obesity in clinical, school, or community-based settings may no longer be enough, Ward said.

“I think we’re going to have to start looking at packaging intervention across multliple measures,” Ward said. “A more holistic approach, and getting at this from different angles is probably the next step we’re looking at.”

The study, "Simulation of Growth Trajectories of Childhood Obesity into Adulthood," was published online in the New England Journal of Medicine.

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