Abstract A76: Associations of sitting time and physical activity with obesity-related cancer risk in Mexican American adults
Authors: Chrisman Matthew , Chow Wong-Ho , Zhao Hua 
Published: May 2016

Abstract
Introduction: The Mexican American Mano A Mano cohort in Houston, Texas is relatively young and cancer incidence is expected to rise as the cohort ages. Identifying risk factors associated with cancer risk is necessary to design culturally-tailored preventive measures. Sitting time, which is now regarded as independent from physical activity (PA), is one potential risk factor for obesity and cancer that has not been well-studied in the Mexican-American population for its associations with cancer risk. This is particularly important for this population as increasing numbers immigrate to the US and adopt habits of sitting more.
Methods: Data on the Mano A Mano cohort, including socio-demographic data and risk factor characteristics, were collected by trained interviewers in participants' homes since 2001. Follow-up data included assessment and verification of cancer and other chronic diseases. Only cases that were verified by the participant's medical record or the Texas Cancer Registry were included in analyses. Baseline data on sitting hours per day and hours per week of moderate and vigorous physical activity (MVPA) were analyzed for their associations with incidence among the main obesity-related cancers in the cohort, including cancers of the breast, prostate, thyroid, colorectum, kidney, and endometrium. Further analyses examined cancer risk in those with the most PA and least sitting time compared to those with the least PA and most sitting time.
Summary of data: Data included 22,998 Mexico-origin adult participants, with 77.6% female. Verified incident cancer was diagnosed in 263 participants, including 123 breast, 28 prostate, 22 thyroid, 36 colorectal, 29 kidney, and 25 endometrial cases. For the entire cohort, mean sitting time was 3.78 (SD 2.58) hours per day, and mean hours per week of MVPA was 2.3 (SD 5.2). Those with incident cancer reported more hours of sitting time per day (4.04 vs. 3.77, P = .092) and less MVPA hours per week (1.74 vs. 2.32, P = .08) when compared to the cancer-free cohort. When comparing those with the highest PA and least sedentary time to those with the least PA and most sitting time, the proportion of overall age-adjusted obesity-related cancer incidence was similar (0.9% to 1.3%, P = 0.10). However, when examining the sex-specific cancers and adjusting for age, significant differences existed for breast (0.9% vs 1.6%, P = .008), endometrial (0.1% vs 0.4%, P = 0.032), and prostate (0.2% vs 1.6%, P &lt; 0.01).
Conclusions: It appears that greater sitting time and lower amounts of MVPA may be associated with higher risk of sex-specific, obesity-related cancer incidence in Mexican American adults, and replication of these findings in larger samples of Mexican-Americans is needed. If confirmed, results suggest that sitting time and PA could be targeted in future interventions to reduce health disparities in Mexican American adults.
Citation Format: Matthew Chrisman, Wong-Ho Chow, Hua Zhao. Associations of sitting time and physical activity with obesity-related cancer risk in Mexican American adults. [abstract]. In: Proceedings of the Eighth AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 13-16, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2016;25(3 Suppl):Abstract nr A76.