A recent study conducted by scientists at the German Cancer Research Center (DKFZ) has shown that the risk factor of obesity for colorectal cancer may have been underestimated.
This is due to the fact that many people unintentionally lose weight in the years before a colorectal cancer diagnosis.
If studies only consider body weight at the time of diagnosis, it obscures the actual relationship between obesity and colorectal cancer risk.
In addition, the current study shows that unintentional weight loss may be an early indicator of colorectal cancer.
Obesity is a known risk factor for a whole range of cancers, including endometrial cancer, kidney cancer, and colorectal cancer.
Previous estimates have suggested that obese individuals have a risk of developing colorectal cancer that is about one-third higher than that of normal weight individuals.
However, many studies have not taken into account that many affected people lose weight in the years before their colorectal cancer diagnosis, leading to the risk contribution of obesity being significantly underestimated in many trials.
To assess the magnitude of this bias, the researchers evaluated data from the DACHS study.
It included nearly 12,000 study participants who had provided information on their body weight at the time of diagnosis and had also reported their weight in the years preceding diagnosis (measured at 10-year intervals).
On the basis of body weight at the time of diagnosis, no indication of a relationship between body weight and colorectal cancer risk could be established.
However, when the researchers looked at the participants’ earlier body weight, they found a strong correlation between overweight and the probability of developing colorectal cancer, which was most pronounced 8 to 10 years before diagnosis.
Study participants who were highly overweight, referred to as obese, during this period were twice as likely as those of normal weight to develop colorectal cancer.
Another trend identified by the researchers was that a striking number of the study participants affected by colorectal cancer had unintentionally lost weight before diagnosis.
An unintentional weight loss of two kilos or more within two years prior to diagnosis (or study entry) occurred 7.5 times more frequently in cancer-affected individuals than in those in the control group.
The findings of the study highlight the need for doctors to regularly ask their patients about unintentional weight loss, as it could be an early indication of colorectal cancer or other cancers and diseases.
It also emphasizes the importance of considering earlier body weight when assessing the relationship between obesity and the risk of colorectal cancer, as only looking at body weight at the time of diagnosis may underestimate the actual risk contribution of obesity.
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The study was published in JAMA Network Open.
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