Fresh evidence links adiposity with multiple cancers
BMJ 2017; 356 doi: https://doi.org/10.1136/bmj.j908 (Published 28 February 2017) Cite this as: BMJ 2017;356:j908
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Park and Colditz think that excess body fat is the second most important modifiable cancer risk factor after tobacco use and it is time to get serious about prevention.1 However, both obesity and cancers can occur in women during short or longer exposures to progestogens and oestrogens.
Rapid weight gain has long been an important reason for first year discontinuation of oral contraceptives and is a problem with long acting progestogen implants. 2-4
Breast cancers increase in the first year of exposure to HRT, and decreases in use lowers breast cancer mortality. 5-8
Is progestogen and /or oestrogen use now regarded as so inevitable that exposures are not even considered as a modifiable cause of cancer although classified as Group 1 carcinogens by the IARC? 9
1 Park Y, Colditz GA. Fresh evidence links adiposity with multiple cancers
BMJ 2017;356:j908 .
2 Mears E, Grant ECG. "Anovlar" as an oral contraceptive. BMJ 1962;2:75-79.
3 Vckery Z, Madden T, Zhao Q, Secura GM, Allsworth JE, Peipert JF. Weight change at 12 months in users of three progestin-only contraceptive methods. Contraception 2013. pii: S0010-7824(13)00090-5.
4 Harel Z, Biro FM, Kollar LM, Rauh JL. Adolescents' reasons for and experience after discontinuation of the long-acting contraceptives Depo-Provera and Norplant. J Adolesc Health. 1996;19:118–23.
5 Chlebowski RT, Hendrix SL, Langer RD, et al. Estrogen plus progestin and breast cancer incidence and mortality in postmenopausal women. JAMA 2003;289:3243-53.
6 Grant ECG. Reduction in mortality from breast cancer: fall in use of hormones could have reduced breast cancer mortality. BMJ. 2005 Apr 30;330(7498):1024
7 Colditz GA. Decline in breast cancer incidence due to removal of promoter: combination estrogen plus progestin. Breast Cancer Res. 2007;9:108.
8 Ravdin M, Cronin KA, Howlander N, Berg CD, Chlebowski RT, Feuer EJ, Edwards BK, Berry DA. The Decrease in Breast Cancer Incidence in 2003 in the United States. NEJM. 2007. 356; 16; .
9 IARC. Combined estrogen-progestogen contraceptives and combined estrogen-progestogen menopausal therapy. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans 2007; Volume 91.
Competing interests: No competing interests
The review of the literature by Kyrgiou1 provided strong evidence supporting the positive association between obesity and cancers. And then Colditz commented that excess body fatness causes cancer2. The positive correlation is not equivalent to causality. Many factors that cause obesity may lead to cancers, and factors that are associated with obesity may also cause cancer. So the statement, that obesity is positively correlated with cancers, cannot be simply interpreted as obesity-carcinogenesis.
There are numerous factors that lead to obesity; unhealthy lifestyle is one of the common ones, such as unhealthy eating patterns and less exercise, which may cause cancers3, 4. In addition, obese people can be at risk of social anxiety, which may also contribute to the carcinogenesis5. Obesity, as well as cancers, are the result of individual behavioral habits, heredity, or environment6.
In the previous systematic review on the relationship between obesity and cancer, there are few subgroup analyses based on influencing factors of obesity, which may be important sources of heterogeneity within studies included in meta-analyses. Therefore, the conclusion, that obesity is positively associated with cancer, is also debatable.
Taking into account various factors of obesity and confounding factors, the viewpoint of obesity-carcinogenesis is inappropriate. If this is not corrected, such an inappropriate conclusion will be very disturbing to obese or overweight people. Maybe these people will take some measures, such as dieting or obesity surgery, to lose weight, but they may not pay much attention to some factors of obesity, which might be the culprit leading to cancers. Palliative measures will eventually lead to the result that loss of weight is of no avail to reduce the risk of cancer.
1. Kyrgiou M, Kalliala I, Markozannes G, et al. Adiposity and cancer at major anatomical sites: umbrella review of the literature. Bmj. 2017;356:j477.
2. Park Y, Colditz GA. Fresh evidence links adiposity with multiple cancers. Bmj. 2017;356:j908.
3. Balakrishnan VS. Physical exercise might affect breast cancer outcomes. The Lancet Oncology. 2016;17:e380.
4. Engbers LH, van Poppel MN, Chin APM, et al. The effects of a controlled worksite environmental intervention on determinants of dietary behavior and self-reported fruit, vegetable and fat intake. BMC public health. 2006;6:253.
5. Blumberg EM, West PM, Ellis FW. A possible relationship between psychological factors and human cancer. Psychosomatic medicine. 1954;16:277-86.
6. Mehl N, Bergmann S, Klein AM, et al. Cause or consequence? Investigating attention bias and self-regulation skills in children at risk for obesity. Journal of experimental child psychology. 2017;155:113-27.
Competing interests: No competing interests
We have known for some time that obesity is a risk factor for several diseases, including some cancers. So why can't healthcare professionals set a good example? Ash Wednesday gives us a good opportunity to resolve to fast during Lent: giving up alcohol and chocolate until Easter would be a good way to start. It is embarrassing to visit people in hospital and find that half the nurses are overweight or obese. We certainly don't want to lose them to cancer, or anything else for that matter. If they have difficulty in losing weight, hospitals should be offering them appropriate therapy: this will save money in the long run.
Competing interests: No competing interests
Re: Fresh evidence links adiposity with multiple cancers
Raloxifene is known to prevent breast cancers.
Raloxifene administration prevents adiposity increases in postmenopausal women. [1][2][3]
Thus, prescribing raloxifene could additionally indirectly reduce all these obesity related cancers.
Despite such overwhelming evidence, GPs still avoid prescribing raloxifene to postmenopausal women. [4]
References
[1] https://www.ncbi.nlm.nih.gov/pubmed/19884264
[2] https://www.ncbi.nlm.nih.gov/pubmed/16837888
[3] https://www.ncbi.nlm.nih.gov/pubmed/16218045
[4] http://www.bmj.com/content/356/bmj.j772
Competing interests: No competing interests