Riverside County Exercise Statistics [1]:

  • 21.2% of adults were sedentary in 2014
  • Only 31.9% of adults say they walk regularly
  • 66.8% of adults are overweight or obese

Overview:

  • Primary risk factors include obesity and type 2 diabetes, which lead to insulin resistance, inflammation, and high levels of sex hormones
  • Physical activity coupled with weight loss reduces adipose tissue and conditions such as insulin resistance, which in turn lowers the risk for many cancers
  • It is estimated that 25% of cancers are due to sedentary lifestyles [2]

Physical Activity Defined:

Physical activity that is coupled with weight loss is incredibly important in reducing the risk of cancer. Physical activity is defined as any movement that requires more energy than resting and uses skeletal muscles [3]. Weight loss results from a decrease in caloric intake combined with physical activity, creating a calorie deficit [4]. Physical activity can be categorized as light, moderate, or vigorous depending on the intensity. To lose weight and keep it off, a high amount of physical activity is required. The chart below provides examples of each intensity level of exercise [4].

 

 

Risk Factors:

It is estimated that 25% of cancers are due to sedentary lifestyles and obesity and type 2 diabetes significantly increase the risk of cancer [2]. Recent findings provide strong evidence that physical activity accompanied by weight loss reduces the risk of colorectal, breast, and endometrial cancers [3]. The mechanisms through which physical activity and weight loss reduce cancer risk become very complicated and include an extensive amount of cell signaling and biology, but mostly come down to one simple fact: weight loss reduces the amount of body fat, which in turn lowers insulin resistance, inflammation, and circulating estrogen levels [3].

Insulin Resistance:

Insulin in healthy individuals regulates blood glucose concentrations [5]. Insulin resistance occurs when cells in muscles, fat, and the liver don’t respond efficiently to  insulin, which makes it difficult for insulin to take up glucose from the blood [5]. This can result from obesity and lack of exercise and results in higher blood glucose levels and higher levels of circulating insulin [6].

Higher levels of insulin have additional complications. Insulin has mitogenic and anti-apoptotic qualities [5]. This essentially means that insulin allows for cell growth while simultaneously preventing cell death, which is crucial in the biology of cancer prevention. The activation of an insulin receptor (IR-A) can induce cell growth and migration to other tissues in many cancer types [5]. In fact, the insulin receptor IR-A is expressed commonly in tumors [5]. Therefore, high levels of insulin can increase the risk of cancer.

Inflammation:

Inflammation is reduced with exercise and weight loss because the amount of adipose tissue (fat) is lowered [5]. The production of pro-inflammatory factors is triggered by a hormone called leptin, which is produced in adipose tissue. Inflammation is especially an issue for people with type 2 diabetes and obese people, as it creates an environment that is favorable towards neoplastic (abnormal tissue growth characteristic of cancer) cell survival and growth [5].

Sex Hormones:

Female sex hormones are important to consider in breast cancer risk. Exercise lowers the risk of breast cancer in women because lower body weight and high physical activity is associated with lower levels of estrogens in the blood [7]. Estrogens and other female sex hormones are elevated in overweight people and are associated with cancer risk [7].

How Physical Activity Reduces Cancer Risk: a Summary [4]

  • Exercise reduces the amount of body fat, which in turn reduces insulin resistance and fasting insulin levels, reduces circulating estrogen levels (in women), and decreases inflammation
  • Exercise improves our immune response, which aids in tumor supervision
  • Exercise can improve DNA repair mechanisms, which leads to suppression of carcinogens

 

References:

  1. Riverside, SHAPE. “Community Health Dashboards.” SHAPE Riverside :: Indicators :: All Data, www.shaperivco.org/index.php?module=indicators.
  2. Duggan, Catherine, et al. “Dietary Weight Loss, Exercise, and Oxidative Stress in Postmenopausal Women: A Randomized Controlled Trial.” Cancer Prevention Research, vol. 9, no. 11, 2016, pp. 835–843., doi:10.1158/1940-6207.capr-16-0163.
  3. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. Physical activity and the risk of cancer. Available at dietandcancerreport.org
  4. “Physical Activity for a Healthy Weight.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 15 May 2015, www.cdc.gov/healthyweight/physical_activity/index.html.
  5. Kamdje, Armel Hervé Nwabo, et al. “Insulin Resistance and Cancer: the Role of Insulin and IGFs.” Endocrine-Related Cancer, Society for Endocrinology, 1 Feb. 2013, erc.endocrinology-journals.org/content/20/1/R1.full.
  6. “Insulin Resistance & Prediabetes.” National Institute of Diabetes and Digestive and Kidney Diseases, U.S. Department of Health and Human Services, May 2018, www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance.
  7. Campbell, Kristin L., et al. “Reduced-Calorie Dietary Weight Loss, Exercise, and Sex Hormones in Postmenopausal Women: Randomized Controlled Trial.” Journal of Clinical Oncology, vol. 30, no. 19, 1 July 2012, pp. 2314–2326., doi:10.1200/jco.2011.37.9792.