A 2018 systematic review by G. A. Colditz and L. L. Peterson noted that the link between obesity and cancer had been studied over the past forty years. Furthermore, more recent studies suggest a causation rather than a simple correlation.
The study also cited the reports from the International Agency for Research on Cancer and the World Cancer Research Fund revealing a link between excess body weight and the development of 13 specific types of cancer.
Findings from another study by M. Arnold et al. showed that both longer overweight duration and the degree of overweightness increased the risk of obesity-related cancer. A calculation of overweight duration and cumulative average overweight years showed obesity-related cancer hazard ratio of 1.36 per 10-year increment.
S. Chadid et al. also concluded that gaining 0.45 kilogram per year over 14 years increases cancer risk by 35 percent. In other words, weight gain during mid-life is a considerable risk factor for the development of obesity-related cancer
Nevertheless, there is indeed a substantial body of evidence linking obesity with cancer. But what exactly is the relationship between excess body weight and cancer? How overweightness or obesity causes the development of cancer?
Explaining the Relationship Between Obesity and Cancer: How Excess Body Weight Causes the Development of Obesity-Related Cancer
Researchers T. W. Stone, M. McPherson, and L. Gail Darlington discussed two hypotheses explaining how obesity serves as a risk factor for cancer development. For starters, the first hypothesis noted that obesity induces hormonal changes and chronic inflammation.
Inflammation activates the kynurenine pathway that, in turn, leads to the activation of the aryl hydrocarbon receptor or AHR. Note that AHR is a transcription factor that regulates gene expression. However, its activation has also been linked to several types of cancer because it promotes tumor development and progression, as well as suppresses the activity of immune cells called T-cells that provide an immune response by killing pathogens and cancer cells.
Another hypothesis is based on how inflammation triggers the release of enzymes called serine proteases. Naturally, these enzymes play a role in coordinating various physiological functions, including digestion, immune response, blood coagulation, and reproduction. They also play a role in cellular proliferation and migration.
However, several studies have revealed that serine proteases have a role in oncogenesis. To be more specific, their release has been found to deplete cells of tumor suppressors such as DCC and neogenin. The absence of these suppressors essentially promotes the proliferation and migration of cells, thus increasing the tendency of these cells to progress to a cancerous state.
It is also important to note that inflammation has been associated with the release of factors and hormones related to cancer development. The study of M. Murata also mentioned that inflammation accounts for about 25 percent of cancer-causing factors. These factors have various mechanisms for promoting carcinogenesis ranging from causing mutagenic DNA lesions to inhibiting tumor-suppressing genes
Stone, McPherson, and Gail Darlington further explained that obesity is a metabolic disorder that subjects affected patients under chronic inflammation due to the dysfunction of insulin and insulin-like growth factors and the release of several pro-inflammatory hormones to include glucagon, leptin, and adipokines.
There is also another link between obesity and cancer. Aside from the fact that obesity is a risk factor for developing cancer, other studies have shown that excess body weight affects cancer progression and mortality or more specifically, of cancer survival, cancer recurrence, and the development of another type of cancer.
In referencing the review study of G. A. Coldtiz and L. L. Peterson again, they explained that case-control studies showed a positive association between BMI and mortality in specific types of cancer, such as breast cancer, prostate cancer, and multiple myeloma. These studies suggest that excess weight due to excess body fat negatively affects cancer prognosis.
Another systematic review by S. E. Jackson, M. Heinrich, R. J. Beeken, and J Wardle mentioned that carrying excess weight has been identified as a risk factor for cancer recurrence, the development of secondary primary cancers, reduced effectiveness of treatment, and complications from the treatment.
Summary and Takeaway: Understanding the Link Between Overweightness or Obesity and the Development of Cancer
There is a two-way link between obesity and cancer. The first is that excess body weight leads to the development of chronic inflammation. Essentially, obesity is a metabolic disorder that is also characterized by dysfunctions in pro-inflammatory mechanisms and the release of pro-inflammatory factors. Note that inflammation induces the release of growth factors and enzymes that have carcinogenic potential.
Second is that excessive body weight affects cancer survival, cancer recurrence, and the development of another type of cancer. Hence, an overweight or obese individual has a lower chance of surviving cancer and responding to treatment while also subjecting him or her to a higher chance of cancer recurrence or the development of a second type of cancer.
Based on the discussions above, weight management and metabolic therapy are crucial in cancer prevention, as well as in the management and treatment of cancer.
FURTHER READINGS AND REFERENCES
- Arnold, M., Leitzmann, M., Freisling, H., Bray, F., Romieu, I., Renehan, A., and Soerjomataram, I. 2016. Obesity and Cancer: An Update of the Global Impact, Cancer Epidemiology. 41: 8-15. DOI: 10.1016/j.canep.2016.01.003
- Chadid, S., Singer, M. R., Kreger, M. E., Bradlee, M. L., and Moore, L. L. 2018. Midlife Weight Gain is a Risk Factor for Obesity-Related Cancer. British Journal of Cancer. 118(12): 1665-1671. DOI: 10.1038/s41416-018-0106-x
- Colditz, G. A. and Peterson, L. L. 2018. “Obesity and Cancer: Evidence, Impact, and Future Directions.” Clinical Chemistry. 64(1): 154-162. DOI: 10.1373/clinchem.2017.277376
- Jackson, S. E., Heinrich, M., Beeken, R. J., & Wardle, J. (2017). Weight Loss and Mortality in Overweight and Obese Cancer Survivors: A Systematic Review. PLOS ONE. 12(1). DOI: 10.1371/journal.pone.0169173
- Murata, M. 2018. Inflammation and Cancer. Environmental Health and Preventive Medicine. 23(1). DOI: 10.1186/s12199-018-0740-1
