Margaret Tyson is an honorary researcher at the Institute of Cancer Sciences, The University of Manchester and runs Manchester Amputee Fitnesss Initiative and Karen's Page
   

The MPHe dissertation was about the link between obesity and cancer worldwide. The prevalence of obesity-related cancers tends to be higher in countries where there is a greater prevalence of obesity either in affluent "Western" countries or where obesity is seen culturally as desirable as in some polynesian countries.

A meta-analysis of all suitable observational cohort studies into the risk of cancer with increased BMI was done where 19 cancers were studied, three of which showed an inverse relationship to obesity, the rest showed a positive relationship. The highest risk due to BMI for men is adenocarcinoma of the oesophagus whereas the highest risk for women is endometrial cancer. Inverse relationships were found for squamous cell carcinoma of the oesophagus, lung cancer and pre-menopausal breast cancer.

The meta-analysis was published in the Lancet.

The mechanisms involved in obesity-related carcinogenesis are complex. They are shown in this schematic representation (Fig. 19 of the dissertation).

To summarise:

Obesity involves an increase in adiposity (fat production) that is important because adipose tissue (fat) is an active endocrine and metabolic organ that affects all tissues. It secretes several hormones and enzymes. Obesity leads to increased insulin and insulin-like growth factor (IGF-1) levels both of which are known to lead to cellular proliferation and cancer. Enzymes such as aromatase convert precursers to sex hormones such as oestrogen which is known to be associated with post-menopausal breast cancer.

 

The relative risk data from the meta-analysis were applied to European population data taken from the dissertation and a paper was published in the International Journal of Cancer where comparisons were made between individual countries and the risk of BMI-related cancers.