(Reuters Health) - Being overweight or obese as a teenager may increase a person’s risk of developing colorectal cancer as an adult, suggests a large Israeli study.

Long-term follow-up of 1.79 million Israeli men and women examined for military service as teenagers showed that overweight and obese teens were over 50 percent more likely to develop colon or rectal cancer by middle age, compared to normal-weight peers.

“The findings from the study show evidence that being overweight and obese in adolescence are associated with an increased risk of subsequent colon cancer in both men and woman,” said Dr. Avni Desai, an oncologist at Memorial Sloan Kettering Cancer Center in New York who wasn’t involved in the study

“Obesity was also noted to have an association with an increased risk of rectal cancer in men,” she told Reuters Health by email.

“Other smaller studies have shown a possible association with obesity and adolescence and future risk of colorectal cancer, but this is the largest study to show the association,” Desai said, adding that in past research the association has been stronger for men.

For the study, published in the journal Cancer, Dr. Zohar Levi, a researcher at Rabin Medical Center and Tel Aviv University and his team analyzed data from millions of Israeli adolescents who underwent compulsory examinations to determine their fitness for military service from 1967 to 2010.

The young men and women were between the ages of 16 and 19 at the time of the examinations, and Levi’s team used a national cancer registry to track who was diagnosed with colon or rectal cancer through December 2012.

The average follow-up was 23 years and the researchers identified almost 2,967 new cases of colorectal cancer in the study group. Among men, there were 1,403 cases of colon cancer and 574 cases of rectal cancer, and among women, 764 colon cancers and 226 rectal cancers.

Being overweight or obese at the initial military examination was associated with 53 percent and 54 percent higher risks of colon cancer for men and women, respectively, compared to normal-weight peers.

In men, obesity was associated with a 71 percent increased risk of rectal cancer, and in women, being obese more than doubled that risk.

Levi did not respond to a request for comments.

This study does have some limitations, said Desai.

“It is looking at a specific group, Israeli Jewish men and women, the studied group included predominantly men. As such it is unclear if the results would be similar in the general U.S. population,” she said.

Additionally, the researchers didn’t have information about adult body weights, so it is unclear whether obese or overweight teens stayed heavy or slim teens gained weight in adulthood.

“The study could not assess whether risk of colorectal cancer was related to adult obesity independent of adolescent obesity,” Desai said. “Also, other risk factors that may affect risk of colorectal cancer such as family history, level of physical activity, diet, and smoking were not reported in the study. Family history is a risk factor for diagnosis of colorectal cancer, especially at a young age.”

Desai noted that although the participants were followed for at least 10 years, they were still fairly young at the end of the study.

“The median age of colorectal cancer diagnosis in the study was 49.4 years, which is younger than the average age of diagnosis of colorectal cancer,” she said, adding that 90 percent of colorectal cancers are diagnosed after the age of 50.

The average age of diagnosis of colorectal cancer in the United States is age 72, she added.

“Again, it is hard to pinpoint the exact causes of colorectal cancer in young patients, what we do know is a healthy lifestyle can reduce the risk of developing cancer. This includes regular exercise, and a healthy diet, low in fat, high in fiber, with less red meats and processed meats,” she said.

SOURCE: bit.ly/2tDgJgk Cancer, online July 24, 2017.