WASHINGTON, Oct. 13 (Xinhua) -- Women who are overweight or obese have up to twice the risk of developing colorectal cancer before age 50 as those who have a normal body mass index.

The study published in this week's JAMA Oncology is the first epidemiologic analysis of the potential contributors to early-onset colorectal cancer, or cases diagnosed under age 50.

The researchers with Washington University and Harvard University used data from 85,256 women ages 25 to 44 in a database starting in 1989. Among them, 114 had been diagnosed colorectal cancer under age 50 till 2011.

Compared with women with the lowest BMIs (18.5 to 22.9 kilograms per square meter), women with the highest BMIs (greater than 30) had almost twice the risk of early-onset colorectal cancer, according to the findings.

The researchers estimated that roughly 22 percent of early-onset colorectal cancer could have been prevented had all participants had a normal BMI between 18.5 and 24.9.

They also found that the higher risk of early-onset colorectal cancer associated with increasing BMI held even among women with no family history of the disease.

"There are few known risk factors for early-onset colorectal cancer," said Edward Giovannucci from the Harvard T.H. Chan School of Public Health.

"If the screening age gets pushed before age 50, BMI may be one of the factors to take into account," said Giovannucci, the paper's co-author.

"Our findings really highlight the importance of maintaining a healthy weight, beginning in early adulthood for the prevention of early-onset colorectal cancer," said co-senior author and cancer epidemiologist Cao Yin at Washington University.

The study is an association one, so it does not establish that increasing weight is a cause of early-onset colorectal cancer.

It is possible BMI could be serving as a surrogate for other risk factors that may influence colorectal cancer risk, including metabolic syndrome and diabetes, according to the researchers.