For all the advances made in the United States in the "war on cancer" over the past 40-plus years, the battle against obesity-related cancer is another story. Case in point: a study(www.cdc.gov) published in Morbidity and Mortality Weekly Report last October. The authors of that study found that although the incidence of cancers not related to overweight and obesity decreased by 13 percent between 2005 and 2014, the incidence of overweight- and obesity-related cancers decreased by only 2 percent during the same period.
Although being overweight or obese has been linked to an increased risk of more than a dozen types of cancer,(www.nejm.org) questions remain about the relationship between obesity at a young age and the prospect of having cancer later in life. Results of a recent systematic review and meta-analysis(onlinelibrary.wiley.com) of observational studies published online in Obesity Reviews have revealed the degree to which being obese increases the risks of several of these cancers. In particular, the results provide compelling evidence that individuals 30 years or younger who are obese are at increased risk of developing various types of cancer later in life. The review also found that as a person's body mass index (BMI) increases, so does the cancer risk.
The authors selected eight cancer types for their review: diffuse large B-cell lymphoma, esophageal adenocarcinoma, gastric cardia cancer, hepatocellular carcinoma, multiple myeloma, pancreatic cancer, renal cell cancer and thyroid cancer.
- A recently published systematic review and meta-analysis found that obesity early in life increases the risks of several types of cancer later in life.
- The research also showed that as a person's body weight increases, so does the cancer risk.
- Family physicians are encouraged to increase patient awareness of the links between obesity and cancer as part of an effort to prevent inappropriate weight gain.
Fifty-six articles published between 1993 and 2018 and representing 27,559 cancer cases met the authors' search criteria.
The final meta-analysis included both cohort and case-control studies. All participants in the selected studies were age 30 or younger. Patient followup ranged from 7.2 years to 40 years, and cancer cases were identified via medical records and cancer registries. All the selected studies reported hazard ratios, odds ratios or relative risks with 95 percent confidence intervals for at least three BMI categories.
In their analysis, the researchers equated relative risks cited in some studies with odds and hazard ratios in other studies. They used two established conversion methods to convert risk ratios into variables for each 5 kg/m2 increase in body weight and a random effects model to calculate summary relative risks for each increase.
The meta-analysis showed that each 5 kg/m2 increase in body weight at a young age was associated with significantly increased risks of each type of cancer. Overall cancer risk increases ranged from 12 percent for thyroid cancer to 88 percent for esophageal adenocarcinoma.
The authors stated that it was difficult to determine exactly when obesity early in life is most likely to increase the development of cancer later in life. However, they pointed to results from other studies(www.nejm.org) that showed that people who were obese as children, teenagers or young adults were more likely to remain obese(eprints.whiterose.ac.uk) into middle and late adulthood. The authors also noted that obesity and cancer share several contributing factors, such as poor diet and lack of physical activity, and that obesity is a risk factor for the onset of a variety of diseases that also contribute to the development of cancer. Given that evidence, the authors stressed the importance of early intervention to prevent patients from becoming obese while they are young.
One important limitation in the meta-analysis was that in most studies, the data on obesity at a young age were obtained retrospectively, which could have led some participants to be placed in the wrong subgroup or category. In addition, some of the biases and confounders inherent in observational studies may have carried over to the meta-analysis' results. For some types of cancer, the data relied on a limited number of studies, and the researchers were unable to come up with any specific associations between obesity and cancer.
The authors nevertheless concluded that higher levels of overweight and obesity at a younger age increase the risks of developing several different types of cancer later in life. They also said it was safe to conclude that preventing young people from becoming overweight or obese may play a significant part in stopping the obesity epidemic and reducing the number of people with obesity-related cancers.
The Role of the FP
Increasing awareness and knowledge of the links between obesity and cancer are important motivational tools family physicians can use to encourage patients to lose weight.
The AAFP supports the recommendations of the U.S. Preventive Services Task Force for screening of children, adolescents and adults as effective ways to prevent inappropriate weight gain and obesity.
Specifically, health care professionals should
- screen children and adolescents 6 years and older for obesity and offer or refer them to comprehensive, intensive behavioral interventions (i.e., multicomponent sessions with a total of 26 contact hours or more over a period of two to 12 months) to promote improvements in weight status; and
- screen all adults for obesity and offer or refer patients with a BMI of 30 or higher to intensive, multicomponent behavioral interventions.
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