An analysis of data from more than 10,000 older adults revealed that each standard-deviation increment in the number of years spent carrying excess weight was linked with a 55% increase in the odds of developing colorectal cancer, researchers report in JAMA Oncology.
"Overweight and obesity have a larger impact on the risk of colorectal cancer - and likely other cancers and other chronic diseases - than disclosed by previous studies that mostly considered body weight measured at a single point in time only," said Dr. Hermann Brenner of the German Cancer Research Center in Heidelberg.
"In our study, by using a novel approach to consider excess weight over a lifetime, a stronger association became evident," Dr. Brenner told Reuters Health by email. "Due to the rising prevalence of overweight and obesity already in younger generations in many countries, (excess weight) may become the number one cancer risk factor besides smoking, accounting for the largest share of cancers in the future."
To take a closer look at the cumulative effect of excess weight on colorectal cancer risk, Dr. Brenner and his colleagues turned to data from DACHS, an ongoing population-based case-control study conducted since 2003 in the Rhine Neckar region of southwest Germany, which covers a population of approximately 2 million inhabitants.
DACHS recruits patients 30 and older with a first diagnosis of colorectal cancer from more than 20 hospitals providing colorectal surgery in the study region. The individuals who make up the control group were selected at a constant rate from population registries. They were matched to cases by age, gender and county of residence.
Trained interviewers collected information on patients and controls using a standardized questionnaire. Individuals in both groups were asked to report their height and weight at diagnosis or recruitment, in the case of controls, as well as their weight at each decennial age, that is, ages 20, 30 and 40 years. The researchers also extracted medical data from hospital records.
The analysis focused on 5,635 patients with colorectal cancer whose mean age was 68.4 years and 4,515 control participants with a mean age of 68.5 years. The researchers defined excess BMI (eBMI) at each year of age as BMI minus 25. For those with a BMI of 25 or less, eBMI was set to zero.
They then summed eBMIs starting at age 20 and ending at either cancer diagnosis or recruitment, in the case of controls, to obtain the weighted number of years lived with overweight or obesity (WYOs).
From the first to the fourth quartile of WYOs, the adjusted odds ratios for developing colorectal cancer rose from 1.25 (95% CI, 1.09 1.44) to 2.54 (95% CI, 2.24 to 2.89) compared with individuals who remained within the normal weight range.
Each standard-deviation increment in WYOs was associated with a significant increase in CRC risk (aOR, 1.55; 95% CI, 1.46 to1.64).
There are probably multiple mechanisms connecting a lifetime accumulation of high BMI to colorectal cancer, Dr. Brenner said. "But a particular important one is chronic inflammation induced by overweight and obesity."
The findings underscore how important excess weight is, Dr. Brenner added.
"Prevention of overweight and obesity to reduce the burden of cancer and other chronic diseases should become a public-health priority," he added. "Since the roots of overweight and obesity are typically and increasingly laid in childhood and adolescence - that is, by adoption of a sedentary lifestyle and poor eating habits - and overweight and obesity acquired at young ages often result in lifelong overweight and obesity, efforts to prevent their development in childhood, adolescence and young adulthood are particularly important."
The new study "makes perfect sense," said Dr. Otis Brawley, professor of oncology and epidemiology at the Johns Hopkins School of Medicine and the Johns Hopkins Bloomberg School of Public Health, in Baltimore, Maryland.
"I believe (the authors) are right and it's very reasonable to advocate that we not get fat and try to do the research to find out why we get fat. Remember, these researchers used European data. While Europeans have a problem with obesity it's not as severe as it is in the U.S."
Back in the 70s just 15% of the population was obese and today it's nearly 40%, Dr. Brawley said. Among Black women in the 70s, 15% were obese as compared to today, when over 60% of African American women are obese, he added.
"This is a good study with an easy lesson: It's relatively non-controversial that we need to focus on what we eat," Dr. Brawley said, adding that the most important goal would be to reduce calories.
SOURCE: https://bit.ly/3uapoqR and https://bit.ly/3trcHcj JAMA Oncology, online March 17, 2022.
By Linda Carroll
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