CME Author: Zeena Nackerdien
Study Authors: Farhad Islami, Ann G. Sauer, et al.
Target Audience and Goal Statement:
Oncologists and primary care physicians
The goal was to explore a study designed to calculate the population attributable fraction (PAF) of incident cancer cases due to excess body weight (EBW) among adults ages 30 or older from 2011 to 2015 in all 50 states and the District of Columbia.
The study investigators posed the following questions:
- What proportion of cancer cases is due to EBW in each state in the U.S.?
- Could information gleaned from the Behavioral Risk Factor surveillance System (BRFSS) be used to help states set priorities for cancer control initiatives?
Synopsis and Perspective:
Weight that is more than what is normally considered a healthy weight for a given height (body mass index [BMI] of 18.5 to <25 kg/m2) is associated with numerous chronic conditions, including cancer. Worldwide, EBW accounted for almost 4% of all cancers in 2012 (544,300 cases, with proportions varying from less than 1% in low-income countries to 7% or 8% in some high-income Western countries and in Middle Eastern and Northern African countries) – a trend expected to rise in the coming years. At least 13 cancer types have been linked to EBW.
The fact that more than one-third of Americans can be classified as overweight (BMI 25-29.9 kg/m2) has been a matter of record since the 1960s; however, obesity (BMI ≥30 kg/m2) has risen dramatically from 13% in the 1970s to 38% in 2014 for obesity overall and from 1% to 8% for class 3 obesity (BMI ≥40 kg/m2). According to the American Cancer Society, carrying EBW is linked to about 8% of all cancers in the U.S., as well as about 7% of all cancer deaths. Risks for many types of cancers are elevated in overweight or obese individuals, including cancers of the breast (postmenopausal women), colon and rectum, endometrium, esophagus, kidney, and pancreas.
The BRFSS is a nationwide telephone survey of adults (ages ≥18) designed to provide reliable state-level estimates of health-related behavioral risk factors, including BMI. American Cancer Society investigators led by Farhad Islami, MD, PhD., scientific director, Surveillance Research, adjusted state-level, self-reported BMI data from the BRFSS (2001-2004) by sex, age, race/ethnicity, and education using objectively measured BMI values from the National Health and Nutrition Examination Survey. The U.S. Cancer Statistics database was used to obtain age- and sex-specific cancer incidence by state.
For this study, the investigators also categorized high BMI (kg/m2) into 4 standard groups, i.e., 25.0-29.9 (overweight), 30.0-34.9 (class 1 obesity), 35.0-39.9 (class 2 obesity), and 40.0 or greater (class 3 obesity).
“Sex-, age-, and state-specific adjusted prevalence estimates for the 4 high BMI categories and corresponding relative risks from large-scale pooled analyses or meta-analyses were used to compute the PAFs for each U.S. state for esophageal adenocarcinoma, multiple myeloma, and cancers of the gastric cardia, colorectum, liver, gallbladder, pancreas, female breast, corpus uteri, ovary, kidney and renal pelvis, and thyroid,” served as the main outcomes and measures according to the authors.
Nationally, there was a higher prevalence of obesity in women than men (41.1% vs 37.9%), especially for class 3 obesity (9.7% vs 5.6%).
About 37,670 cancer cases in men (4.7% of all cancer cases minus non-melanoma skin cancers) and 74,690 cancer cases in women (9.6%) ages 30 and older in the U.S. were due to EBW (2011-2015). The investigators found at least a 1.5-fold difference between states with the highest and lowest proportions of cancers linked to EBW. The PAF for men ranged from 3.9% (95% CI, 3.6%-4.3%) in Montana to 6.0% (95% CI, 5.6%-6.4%) in Texas. The PAF almost doubled for women, ranging from 7.1% (95% CI, 6.7%-7.6%) in Hawaii to 11.4% (95% CI, 10.7%-12.2%) in the District of Columbia.
“It is noteworthy that states with relatively low overall cancer incidence rates will have a high PAF for cancer associated with EBW if they have a high EBW prevalence,” Islami’s group explained. “For example, although the overall age-standardized cancer rate in women was higher in Connecticut than in Alaska (526.7 vs 447.7 per 100,000 people in 2010-2014), Connecticut had a lower PAF for cancer associated with EBW than Alaska (8.2% vs 10.4%), reflecting its lower EBW prevalence (adjusted prevalence of 57.7% vs 64.3%, respectively, in 2001-2004).”
Substantial percentages of individual tumors of the esophagus, liver and gallbladder, kidney and renal pelvis, and endometrial cancer could be attributed to EBW. Carcinoma of the epithelial lining (endometrium) of the uterine corpus ranged from 36.5% to 54.9% across states and was ≥50% in 19 states.
Alaska, the District of Columbia, and mainly southern and Midwestern states were found to have the largest PAFs.
Study limitations included the fact that the PAFs for some of the less populated states were based on small sample sizes, the fact that BMI is an indirect measure of EBW (as it includes both body fat and lean body mass), and the choice of the lag period between BMI prevalence and cancer occurrence can affect PAFs when prevalence changes over time.
Source Reference: JAMA Oncology, Dec. 27 2018, doi:10.1001/jamaoncol.2018.5639
Study Highlights: Explanation of Findings
The proportion of cancers due to EBW ranged from 3.9% to 6.0% among men and from 7.1% to 11.4% among women, in this nationwide cross-sectional study of adult Americans. Several southern and Midwestern states, Alaska, and the District of Columbia had the highest proportions of cancer. The larger PAF in women vs men may be reflected in an increased risk of numerous female-specific cancers (corpus uteri, female breast, and ovary) and the higher prevalence of class 3 obesity noted among women vs men across all states in this analysis. Overall, cancer cases linked to EBW ranged from a low of 5.9% in Hawaii to a high of 8.3% in the District of Columbia.
The use of representative exposure and cancer occurrence data and relative risks (RRs) of specific types of cancer for each level of EBW to calculate PAF estimates by state (along with their CIs) were cited as major strengths of the study. Another study strength was the fact that the investigators adjusted self-reported BMIs using objectively measured BMIs to provide more accurate PAF estimates.
EBW accounted for at least 1 in 17 of all incident cancers in each state, increasing substantially for some cancers. “Broad implementation of known community- and individual-level interventions is needed to reduce access to and marketing of unhealthy foods (e.g., through a tax on sugary drinks) and to promote and increase access to healthy foods and physical activity, as well as preventive care,” according to the authors.
They also added that “the US Preventive Services Task Force recommends EBW screening for adults by primary care physicians and offering or referring individuals to intensive behavioral interventions if they are obese (BMI, ≥30 kg/m2); if they are overweight (BMI, 25.0-29.9 kg/m2) with hypertension, dyslipidemia, abnormal blood glucose, or diabetes; or if they are normal weight (BMI, 18.5-24.9 kg/m2) with abnormal blood glucose or diabetes.”
Islami and colleagues also suggested that interventions at the community level could include establishment of a safe infrastructure for exercise and facilitating the formation of grocery stores stocked with fresh fruits and vegetables in underserved areas, since EBW seemed to be more common in lower socioeconomic groups in the U.S.
Taken together, the investigators noted that healthcare providers and policymakers, both at the state and federal level, must support efforts to reduce obesity and healthcare disparities that are apparent between states. “Further research to identify tailored and more efficient strategies for reducing the prevalence of EBW is also needed,” they added.
Kristen Monaco wrote the original story for MedPage Today.