Disentangling the complex relationship of obesity and colorectal cancer risk
By Susanne F Meisel, on 8 May 2014
One of the groups most at risk of colorectal cancer – the severely obese (BMI ≥ 40) – appear to be less likely to take up colorectal cancer screening than people in lower weight categories.
We know from previous research that obese individuals are not only more likely to be diagnosed with both colorectal cancer and breast cancer, but also more likely to die from them. However, because earlier detection of these cancers increases chances of survival, researchers from our department wanted to know whether lower rates of cancer screening participation in this group might play a part in their comparatively poorer survival rates.
The NHS breast screening programme invites women aged 50 to 70 (extended to 74 in some areas) for screening by mammography every three years . which is carried out by a health professional. In contrast, in the NHS Bowel Screening Programme, men and women aged 60–69 (which will be extended to 74) are sent a Faecal Occult Blood Testing kit (FOBT) every two years which they complete at home and return for analysis.
The research was conducted with 1,804 persons eligible for NHS colorectal screening and 2,401 persons eligible for NHS breast screening in the UK, who were each asked if they had ever been screened and if this was part of the NHS screening programme. Of those, 131 were severely overweight.
The results showed that an individual’s weight has no impact on whether or not they are likely to attend breast cancer screening (in fact overall rates are high at 92%). However, weight does affect participation in colorectal cancer screening. We found that rates of colorectal cancer screening decreased as weight increased, and that those who are severely obese, are significantly less likely than their lean counterparts to take part in colorectal screening (just 45% reported participating, compared to the overall rate of 63%).
So, delayed detection may play a role in the relationship between overweight and the risk of being diagnosed later, when colorectal cancer may be more advanced. As these findings come from a large sample of people, it is unlikely that these results were due to chance. But why might weight impact whether or not a person participates in colorectal cancer screening but not breast cancer screening? Perhaps heavier people find it difficult to actually carry out the colorectal screening test, which they are required to do at home, as it necessitates a certain amount of flexibility and mobility and we know obesity is associated with mobility problems, particularly in older adults. This is speculation at the moment, and it is likely other factors are involved. We did not ask participants why they did not attend screening, so more research needs to be done to find out more about attitudes to cancer screening.
This could help us to develop interventions that might help combat the double disadvantage these individuals face, in terms of having both a higher risk of developing colorectal cancer and a lower uptake of screening. The NHS is currently rolling out a different method of colorectal cancer screening, in which people will receive a flexible sigmoidoscopy which, like mammography, is a procedure carried out by Health Professionals. It will be interesting to see whether there are still differences in participation for this method of screening according to weight status.
Beeken RJ, Wilson R, McDonald L, Wardle J. Body mass index and cancer screening: Findings from the English Longitudinal Study of Ageing. Journal of Medical Screening, published online first 22nd April, 2014. doi:10.1177/0969141314531409