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SAN DIEGO -- Excess weight in childhood appears to boost the risk of obesity-related cancers for men later in life, even if they shed the extra pounds by adulthood, a researcher reported here.

Over more than 40 years of follow-up, men who were overweight or obese at age 8 but returned to normal weight by age 20 were 38% more likely to develop cancers compared with those at normal weight throughout development (adjusted hazard ratio [aHR] 1.38, 95% CI 1.09-1.75), reported Jenny Kindblom, MD, PhD, of the University of Gothenburg in Sweden.

Males who were overweight at age 8 and stayed overweight at age 20 faced a 66% higher cancer risk (aHR 1.66, 95% CI 1.18-2.33), according to findings presented at the Obesity Week annual meeting.

"A childhood overweight trajectory is associated with increased risk of obesity-related cancer independent of the later BMI [body mass index] trajectory," Kindblom told Medpage Today. "The finding here is new."

For the study, researchers tracked 36,566 men born from 1945 to 1961 in Sweden, who were conscripted for mandatory military service when that was required for men. Of those, 6.3% were overweight at age 8 and 7.4% were overweight at age 20. (The team calculated BMIs for those ages via data for ages 6.5-9.5 years and 17.5-22.0 years.)

During the mean 41.3-year follow-up period, 1,562 men (4.3%) were diagnosed with obesity-related cancers -- including oral, esophageal, gastric, colorectal, liver, thyroid, gallbladder, pancreatic, male breast, and kidney cancers, as well as melanoma, meningioma, lymphoma, multiple myeloma, and leukemia. Of those, 570 died.

Absolute cancer risks were highest in those who were overweight both at age 8 and 20 years (6.7%), followed by those who were overweight at age 8 but returned to normal weight by age 20 years (5.4%), those of normal weight at both ages (4.2%), and those who were normal weight at age 8 but overweight at age 20 (4.1%).

"Independent of your BMI in young adulthood at 20 years, overweight at age 8 adds to your risk of obesity-related cancers," Kindblom said.

In another analysis, men who were overweight at age 8 were 51% more likely than others to develop the cancers (aHR 1.51, 95% CI 1.26-1.80), and those overweight at age 20 were 25% times more likely (aHR 1.25, 95% CI 1.05-1.49).

The researchers adjusted the statistics for birth year, country of birth, and education level. "There are some more confounding factors we would have loved to be able to adjust for, such as lifestyle factors and overweight later during the adult period," Kindblom said.

She noted that other studies have linked childhood obesity to cancer in adulthood, including that connected higher childhood BMI to a 24% higher risk of cancer mortality. "However, the previous studies have not been able to study BMI during childhood independent of young adult BMI. What we've done that's new is evaluate overweight at age 8 years independent of overweight in young adult age."

What might explain the excess cancer risk in males who lost their extra childhood weight by age 20?

"My guess is that when BMI is high early in life, there is a time window for programming -- perhaps mediated through IGF [insulin growth factor]-1/insulin or perhaps other factors -- that causes adverse physiological changes leading to a generation of risk of obesity-related cancer," said Kindblom.

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