Ata Akhtari kohnehshahri,1Fatemeh Bayati,2Nazanin Reisi,3Esmaeil Shaker,4Parsa moeini,5fereshteh gholami,6,*
1. Student Research Committee, Faculty of medicine, Tabriz Medical Sciences, Islamic Azad University, Tabriz, Iran 2. Student Research Committee, Kermanshah university of medical science, Kermanshah , Iran 3. Medical student, Mazandaran university of medical science, Mazandaran, Iran 4. Medical student, Ardabil university of medical science, Ardabil, Iran 5. Medical student, Esfahan university of medical science, Esfahan, Iran 6. Student Research Committee, Bushehr University of Medical Sciences, Bushehr, Iran
Introduction: Obesity is a major risk factor for developing cancer. The number of cancers caused by obesity is estimated at 20% with the increase risk that malignancies are influenced by diet, weight change and body fat distribution as well as physical activity. These results are alarming, as the world experiences a pandemic of obesity and, therefore, insulin resistance. Obesity can increase the risk of various types of cancer through several mechanisms, including increased sex and metabolic hormones and inflammation. Despite this knowledge, knowledge of the existence of these associations remains limited. The purpose of this review article was to summarize the epidemiological evidence related to the contribution of physical activity, sedentary behavior and obesity to cancer etiology and to provide insight into the biological mechanisms that may mediate between these factors and cancer incidence.
Methods: In the forthcoming systematic study, the required data were collected using keywords and citing valid databases such as: Scopus PubMed, Google Scholar and ProQuest. The statistical population of the study includes all studies conducted up to 2022 in the field of Physical activity, obesity and cancer mechanisms, a total of 17 articles were analyzed.
Results: Strong and consistent evidence exists that higher levels of physical activity reduce the risk of six different tumor sites (bladder, breast, colon, endometrium, esophageal adenocarcinoma, gastric cardia), while moderate evidence inversely associates physical activity with lung, ovarian, pancreatic and kidney cancer and limited evidence inversely correlates physical activity with prostate cancer. Sedentary behavior independent of physical activity has been shown to increase the risk of colon, endometrial and lung cancer. Obesity is a consistent risk factor for 13 different tumor sites (endometrial, postmenopausal breast, colorectal, esophagus, kidney/kidney, meningioma, pancreas, gastric cardia, liver, multiple myeloma, ovary, gallbladder, and thyroid).The association between obesity and increased cancer risk is mainly due to anthropometric parameters and lifestyle factors that activate different biological mechanisms. The anthropometric parameters are BMI, weight gain and the amount of body fat, especially visceral. Lifestyle factors include sedentary habits and dietary parameters, such as a high-calorie and/or low-quality diet. The most important biological mechanisms that mediate the adverse influence of the above factors are hyperinsulinemia and insulin resistance, the activities of IGFs and IGF binding proteins, sex hormones and SHBG, general and adipose tissue low-grade inflammation, changes in adipose tissue production of adipokines and vascular growth factors, oxidative stress, endocrine disruptors, and alterations in immune function. We still don't have clear scientific evidence that avoiding or gaining weight significantly reduces cancer risk.
Conclusion: In conclusion, physical inactivity and obesity independently increase the risk of multiple cancers, and some evidence that sedentary behavior has a similar effect. High BMI is a main risk factor that continues to increase in prevalence, even in developing countries. Increases in urbanization, sedentary jobs, and leisure-time spent at the computer or watching television have further led to inactive lifestyles and increase the risk of multiple noncommunicable diseases. Knowledge resulting from this research may be used to identify an obesity phenotype that is particularly strongly associated with cancer risk, and thus pave the way for targeted prevention of cancer morbidity and mortality. Additional research is needed to increase the depth and scope of knowledge pertaining to these associations.