Cancer risk is higher for overweight people
A person's chances of developing cancer can depend on how much they weigh, according to a study by Bern University researchers.
But the research showed that having a high Body Mass Index (BMI) doesn’t just increase the risk, but also that women and men react differently when overweight.
BMI is calculated by taking your weight and dividing it by your height squared. If the number is higher than 25, then you are overweight.
The researchers in Bern and colleagues at Manchester University looked at more than 140 scientific articles reviewing the relationship between specific cancers and BMI published over a period of 40 years.
The study considered 20 different common types of cancer using the same guidelines, and the results showed that a gain of five BMI points led to a clear increase in the number of cases of intestinal, thyroid, kidney and oesophageal cancer.
“If the BMI index is five points higher for men, their chances of getting colon cancer will increase by 24 per cent for example,” said Marcel Zwahlen, an epidemiologist and one of the study’s authors. “Another five points would mean an almost 50 per cent increase.”
Gender differences
The Bern study, the results of which are published in the medical journal The Lancet, broke new ground by looking at differences between the sexes. Overweight men and women are not equal when it comes to cancer risk.
Women are more likely to contract breast cancer, but also gall bladder or pancreatic cancer. Men are more likely to be affected by conditions such as skin melanomas or colon cancer, one of the most common types.
“Colon cancer shows a marked difference between men and women, with men far more susceptible to contracting the disease,” said Zwahlen.
“It’s plausible that there is a real difference in the results because of the differences in men’s and women’s hormonal and insulin systems.”
But he adds there is no guarantee that biology is the sole reason for these differences.
“Can you rely on figures given by women, which lead a lower association between cancer and BMI?” he told swissinfo. “Women tend not to always tell the truth about their weight.”
Geographical differences
Besides considering differences between men and women, the researchers tried to see if geography also played a role. The articles used for their data were divided into three zones: North America, Europe (including Australia) and Asia/Pacific.
The result was that there were no significant differences between these zones, something that Zwahlen says is not that surprising given that basic human biology varies little from one place to another.
The only exception they found was for breast cancer.
“There was a stronger association with BMI for this condition in the Asia/Pacific region. The underlying mechanisms should be clarified,” added Zwahlen.
Lifestyle factors such as diet, smoking and activity were also considered for the study. However, there was little difference between the results of journal articles that looked closely at these qualitative factors and those that didn’t.
The authors say that the next step will now be to understand how BMI actually influences cancer risk, an explanation that cannot be drawn from the data they have studied.
swissinfo, Scott Capper
BMI provides a measure of a person’s “fatness” or “thinness”, allowing health professionals to discuss weight problems with their patients.
BMI is controversial however because it is often used for medical diagnosis, when it was actually meant to be used as a simple means of classifying sedentary individuals with an average body composition.
For these people, a BMI of 18.5-25 may indicate optimal weight; a BMI lower than 18.5 suggests the person is underweight while a number above 25 may indicate the person is overweight; a BMI below 17.5 may indicate the person has anorexia or a related disorder; above 30 suggests the person is obese and over 40 morbidly obese.
After cardiovascular diseases, cancer accounts for the second-highest number of deaths in Switzerland; 28% of men and 22% of women die from the disease.
Every year, 31,000 new cases of cancer are recorded in Switzerland, and 15,000 cancer-related deaths.
Worldwide, cancer kills 11 million people a year (12.5% of all deaths).
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