The impact of obesity as a cancer risk factor

WORLD Obesity Day

 

It is estimated that 20% of all cancers worldwide are caused by obesity [1]. A combination of diet, weight change, body fat distribution and lack of exercise contribute towards the link between excess weight and increased cancer risk. Obesity heightens the risk of cancer development at different rates in different tissues, and common cancers associated with obesity are postmenopausal breast, endometrial, oesophageal adenocarcinoma, colorectal, prostate and renal [1].

There are various biological mechanisms linking abdominal obesity to increased cancer risk [1]. Adipose tissue, or fat, secretes adipokines, leptin and adiponectin; this promotes hyperinsulinemia and secretion of insulin-like growth factor 1 and endogenous sex steroid hormones, all of which have been associated with altering tumour cell signalling and metabolism [2]. For instance, in the breast, adipose tissue was found to elevate oestradiol and leptin secretion and upregulate oestrogen receptor expression. This was found to significantly increase the risk of developing hormone receptor–positive breast cancer in postmenopausal women who were not undergoing hormone replacement therapy. Obesity also worsened prognosis and significantly decreased the chance of survival in these patients [3].

It is now accepted that obesity is the second biggest preventable risk factor for cancer development after smoking, and many national and international health organisations are working to inform the general public of this association. In fact, the American Institute for Cancer Research suggests that maintaining a healthy diet together with exercise is the best measure for cancer prevention after giving up smoking [4], and the National Cancer Institute lists obesity as a preventable risk factor for cancer [5]. Additionally, the World Health Organization is working to improve awareness of the common health consequences of obesity, including common cancers [6], while Cancer Research UK (CRUK) is pushing for government action to create an environment in which healthy lifestyle choices are more accessible [7].

In spite of efforts to raise awareness by these health organizations, and the substantial body of evidence showing that obesity is a risk factor for cancer, awareness of this connection is still low compared with other preventable risk factors such as smoking and the use of tanning beds [8–11]. This lack of awareness is the result of multiple factors. For example, a recent letter to the editors of the British Medical Journal explained how information about obesity being a preventable risk factor for cancer was either lacking, incomplete or speculative throughout the UK school curriculum [12]. Surprisingly, advice or education about healthy weight levels is rarely given by healthcare professionals, even in cases where patients have already developed cancer [11]. A report produced by Narrative Health for CRUK found that most GPs find it difficult to deliver advice on healthy weight management to patients unless they are directly prompted about it. The main reasons behind this were found to be fear of offending the patient, lack of time and a perception of low impact [13].

A report by CRUK in 2018 predicts that if current trends continue, overweight and obesity will cause more cancer cases than smoking by 2043 and will cause 40,800 cancers in the UK in 2035 alone [14]. These figures, along with the lack of awareness of both the UK and the worldwide general public, urge local and global action.

Obesity is a vastly complex issue combining economic, social and cultural factors together with lifestyle choices. We live in an obesogenic environment and navigating it can be difficult when trying to make healthy life choices. Raising awareness about the link between obesity and cancer is intended to help people make more informed decisions – not to stigmatise them or tell them what to do. Raised awareness can also influence the implementation of government policies that make it easier for people to make healthy lifestyle choices, with the hope of lowering the rise in obesity in the future.

 

References

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  2. Hopkins BD, Goncalves MD and Cantley LC. Obesity and cancer mechanisms: Cancer metabolism. J Clin Oncol 2016; 34 (35): 4277–4283.
  3. Gérard C and Brown KA. Obesity and breast cancer – role of estrogens and the molecular underpinnings of aromatase regulation in breast adipose tissue. Mol Cell Endocrinol 2018; 466: 15–30.
  4. American Institute for Cancer Research. Obesity and cancer risk. Available at: https://www.aicr.org/reduce-your-cancer-risk/weight/reduce_weight_cancer_link.html. Accessed October 2019.
  5. National Cancer Institute. Obesity and cancer. Available at: https://www.cancer.gov/about-cancer/causes-prevention/risk/obesity/obesity-fact-sheet. Accessed October 2019.
  6. World Health Organization. Obesity and overweight. Available at: https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight. Accessed October 2019.
  7. Cancer Research UK. Tipping the scales: Why preventing obesity makes economic sense. Available at: https://www.cancerresearchuk.org/sites/default/files/tipping_the_scales_-_cruk_full_report11.pdf. Accessed October 2019.
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  9. Hooper L, Anderson AS, Birch J et al. Public awareness and healthcare professional advice for obesity as a risk factor for cancer in the UK: A cross-sectional survey. J Public Health (Oxf) 2018; 40 (4): 797–805.
  10. Lagerlund M, Hvidberg L, Hajdarevic S et al. Awareness of risk factors for cancer: A comparative study of Sweden and Denmark. BMC Public Health 2015; 15: 1156.
  11. Connor EV, Raker CA, Clark MA et al. Obesity risk awareness in women with endometrial cancer. Arch Gynecol Obstet 2017; 295 (4): 965–969.
  12. Renehan AG, Lloyd K and Renehan I. Awareness of the link between obesity and cancer in UK school curricula. Lancet 2019; 393 (10181): 1591–1592.
  13. Narrative Health. Project impact: An evaluation of the RCGP CRUK Behaviour Change and Cancer Prevention e-learning module. Available at: https://www.cancerresearchuk.org/sites/default/files/project_impact_report_mar_19_18.pdf. Accessed October 2019.
  14. Cancer Research UK. When could overweight and obesity overtake smoking as the biggest cause of cancer in the UK? Available at: https://www.cancerresearchuk.org/sites/default/files/obesity_tobacco_cross_over_report_final.pdf. Accessed October 2019.