“A pot belly is a red flag for cancer,” reports the Mail Online after a new study found an increase in waist circumference carries similar risks for developing cancer as raised body mass index (BMI).
The study used data from several European studies of more than 43,000 adults aged around 63, who were then followed up for 12 years.
Researchers found for every 11cm increase in waist circumference, the overall risk of getting one of 10 types of obesity-related cancers (such as kidney and liver cancer) increased by 13%.
The increase in risk was higher for colorectal cancer, at 22%.
This was a large study that took into account a number of factors known to cause cancer, such as smoking.
But it also overlooked other important factors, such as whether participants had any other medical condition, their medication use, or other previous treatments. This reduces the reliability of the results.
Nevertheless, the findings are in line with other research, which shows excess weight increases the risk of certain cancers.
Where did the story come from?
The study was carried out by researchers from the International Agency for Research on Cancer, Queen’s University Belfast, the Hellenic Foundation in Greece, and numerous other institutions across Europe and the US.
It was funded by the European Commission, the World Cancer Research Fund, and governments from Greece, Norway, Denmark, Spain, Germany, Northern Ireland, and the Netherlands.
The UK media generally reported the story accurately, but failed to put the increased risk into context.
What kind of research was this?
Though cohort studies cannot prove that one factor (such as excess weight) causes a condition (such as cancer), it’s the most appropriate type of research when randomised controlled trials aren’t possible because of practical or ethical concerns.
High body mass index (BMI) is already linked to an increased risk of 11 different cancers.
But it’s not yet clear whether the distribution of excess body fat, such as abdominal obesity (a “pot” or “beer belly”), could provide a more accurate prediction of risk.
What did the research involve?
The researchers reanalysed data from seven large prospective cohort studies from Europe participating in the Consortium on Health and Ageing: Network of Cohorts in Europe and the United States (CHANCES) study.
They looked at individual data for 43,419 adults who’d been followed up over an average of 12 years. Their average age at entry into the study was 63, ranging from 50-84.
They investigated whether different measures of weight and body fat distribution were linked to the development of various cancers during the study periods.
They took into account the following potential confounding factors:
- age at entry into the cohort
- smoking status (never, former, current, missing)
- physical activity (vigorous, at least once a week, or not)
- daily alcohol intake
- level of education
- use of hormone therapy in women
What were the basic results?
Over the 12-year follow-up period, 1,656 people developed one of the following cancers proved to be related to obesity:
- postmenopausal female breast cancer
- colorectal cancer
- lower oesophageal cancer
- stomach cancer
- liver cancer
- gallbladder cancer
- pancreatic cancer
- endometrial cancer
- ovarian cancer
- kidney cancer
The researchers didn’t include prostate cancer, as only advanced cases have been linked to obesity and they lacked this information.
Results were expressed in terms of the raised risk for every standard deviation (SD) according to four measures of body fat.
For each 10.8cm (1 SD) increase in waist circumference, the risk increased by:
- 13% for any obesity-related cancer (hazard ratio [HR] 1.13, 95% confidence interval [CI] 1.04 to 1.23)
- 21% for colorectal cancer (HR 1.21, 95% CI 1.08 to 1.35)
- 21% for postmenopausal breast cancer for women who hadn’t used hormone replacement therapy (HR 1.21, 95% CI 1.05 to 1.40)
For each BMI increase of 4kg/m2, the risk increased by:
- 11% for any obesity-related cancer (HR 1.11, 95% CI 1.02 to 1.21)
- 16% for colorectal cancer (HR 1.16, 95% CI 1.04 to 1.30)
- 22% for postmenopausal breast cancer for women who hadn’t used hormone replacement therapy (HR 1.22, 95% CI 1.08 to 1.38)
For each 0.08 increase in the waist to hip ratio, the risk increased by:
- 20% for colorectal cancer (HR 1.20, 95% CI 1.05 to 1.37)
- 24% for postmenopausal breast cancer for women who hadn’t used hormone replacement therapy (HR 1.24, 95% CI 1.08 to 1.42)
Each increase of 8cm in hip circumference increased the risk of colorectal cancer by 15% (HR 1.15, 95% CI 1.01 to 1.32).
There was no association between these measures and overall risk of postmenopausal breast cancer or risk for women who’d been on hormone replacement therapy.
How did the researchers interpret the results?
The researchers concluded that increases in all four measures of body fat distribution show similar “associations with obesity-related cancers combined and with colorectal cancer in older adults”.
The higher risk of postmenopausal breast cancer with increasing weight was only found in women who’d never used hormone therapy.
The researchers say that, “Overall, our results underscore the importance of avoiding excess body fatness for cancer prevention irrespective of age and gender.”
This study provides more evidence of the link between excess body fat and 10 cancers. Though the percentage increases sound large, it’s important to put these results into context.
For example, the baseline risk of postmenopausal cancer was 2.2% – it occurred in 555 of the 24,751 women in the study.
For women who hadn’t used hormone therapy, this would increase to a risk of 2.7% if they had a BMI of 30 compared with 26, or a waist circumference of 95cm compared with 84cm. This accounts for only an extra 5 cases in every 1,000 women.
This large study involved older adults from European countries, so the results should be applicable to people in the UK.
Its strengths also include the fact researchers analysed data for each individual rather than relying on published results from each study, which could have used different definitions and cut-offs.
As ever, though, there are some limitations to be aware of:
- There were differences between the cohorts, such as length of follow-up and age at entry into the study.
- Other medical conditions and medication weren’t included in the analysis.
- Diet wasn’t taken into account.
- Though the researchers looked at smoking, physical activity, and alcohol, they weren’t able to analyse the results for different amounts of each.
- The obesity-related cancers were combined in the analysis because of small numbers, so we don’t know if there was variation in risk between them.
- The length of follow-up may not have been long enough for some cancers to develop.
The study does add to the growing body of research that indicates a healthy BMI, waist circumference, and waist to hip ratio reduces the risk of cancer and other conditions, such as diabetes.
Edited by NHS Choices