Men who were overweight as children are likely at higher risk for infertility, a recent study suggests.

To investigate the impact of obesity-related metabolic disorders on testicular growth, scientists at the University of Catania in Sicily looked at health records from 268 boys aged 2 to 18 years old. The boys had all been referred to the institution for weight control. Among them were 62 boys who had a normal weight, 54 who were overweight, 79 who were obese, and 73 who were severely obese.

Their findings, published in April in the European Journal of Endocrinology, show that boys with normal weight had 1.5 times higher testicular volume than their peers who were overweight or obese before puberty, and that boys with normal insulin levels had as much as 2 times greater testicular volume than boys with elevated insulin levels.

“We found that being overweight or obese was associated with a lower peri-pubertal testicular volume,” the researchers wrote. “In addition, obesity-related comorbidities, such as hyperinsulinemia and insulin resistance, have been found to influence testicular volume in pre- and post-puberty.”

Hyperinsulinemia is the condition where the amount of insulin in the blood is higher than what’s considered healthy. The team’s previous study showed boys with hyperinsulinemia tended to have lower testicular volume.

Since testicular volume is a fertility predictor directly related to sperm count, the scientists said they believe that careful weight control would help boys avoid infertility when they become adults.

“We speculate that more careful control of body weight in this time window could represent a prevention strategy to pursue the maintenance of testicular function later in life,” they wrote.

The global rise of childhood obesity largely coincides the decline of sperm counts in men across the world.

Over the last 50 years, average sperm concentrations dropped by 51.6 percent, and total sperm counts dropped by 62.3 percent, according to a meta-analysis published in November in the European journal Human Reproduction Update.

The analysis covers 223 papers published between 1973 and 2018 involving sperm samples collected from a total of 57,000 men across 53 countries in all continents. It found that average sperm concentrations have dropped from 104 million to 49 million per milliliter of semen.

Researchers said that fertility drops off rapidly below a sperm concentration of 40 million per milliliter.

The rate of decline also appears to be increasing. Looking at data collected since 1972, the researchers found sperm concentrations declined at a rate of 1.16 percent each year. However, when they looked only at data collected after 2000, they found a 2.64 percent fall each year.

At the same time, the number of children and adolescents with obesity has skyrocketed worldwide. According to the World Health Organization, in 1975 an estimated 5 million girls and 6 million boys were obese. By 2016, those numbers had risen to an estimated 50 million girls and 74 million boys.

In the United States, childhood obesity is becoming more common, despite public health campaigns promoting healthy eating and active living.

In an August 2022 study published in Pediatrics, researchers compared data on children entering kindergarten in 1998 and in 2010 and followed them through fifth grade. They found that 16.2 percent of children who had a healthy weight when they started kindergarten in 2010 were obese by the end of fifth grade, compared with 15.5 percent of children who started kindergarten in 1998. Children in the 2010 group also became obese at younger ages than those in the 1998 group.

According to the Centers for Disease Control and Prevention (CDC), about 1 in 5 American children has obesity. When broken down by age groups, obesity affects 12.7 percent of children aged 2 to 5 years, 20.7 percent of children aged 6 to 11 years, and 22.2 percent of adolescents aged 12 to 19 years.

The widespread COVID-19 pandemic lockdowns and school closures have also worsened childhood obesity, as children across the country engaged in less physical activity, slept more, and used screens more. They also increased their consumption of unhealthy snacks and drinks.

A 2021 study by the CDC looked at health data of 432,302 people between the ages of 2 and 19 years old and found that the percentage of obese children and teens increased to 22 percent, compared with 19 percent before the pandemic.