A new study finds that the higher your BMI, the more likely you are to develop the 10 most common cancers. What does this link mean for our health and does it change how we should approach fighting cancer?
The study, published this month in the Lancet, is the largest of its kind and involved analyzing GP records from 5.24 million adults aged 16 and over from the UK who were cancer free at the time the analysis began and were followed for an average of seven and a half years.
The researchers found that for every five percentage point rise in someone’s BMI above the predetermined healthy average, there was a substantial increase for 10 of the most common cancers we see today, including cancer of the uterus, cervix, thyroid, kidney, liver and colon.
To give examples of the increased risk, the scientists determined that a five point increase in BMI raised the risk of developing cancer of the uterus by 62 percent, while kidney cancer went up by about 25 percent, and gallbladder cancer risk went up by 31 percent. In total, the researchers estimated that all this adds up to 12,000 new cases of cancer every year. They also project that by 2026, rising obesity rates could account for an extra 3,790 extra cancer cases per year.
Lead researcher Dr Krishnan Bhaskaran is quoted as saying: “The number of people who are overweight or obese is rapidly increasing both in the UK and worldwide. It is well recognized that this is likely to cause more diabetes and cardiovascular disease. Our results show that if these trends continue, we can also expect to see substantially more cancers as a result. The higher the BMI, the higher the risk.”
It should be said that BMI is a controversial topic because it’s not necessarily indicative of poor health. BMI or body mass index is calculated using a person’s height and mass to get their relative weight or, to put it another way, their thickness or thinness. A BMI score of 18.5 to 25 usually puts someone within the optimal “healthy” bracket. A BMI under 18.5 and a person is probably underweight for their height. A BMI over 25 and people are usually overweight, and over 30 suggests the person is probably obese.
However, certain body types confound BMI because it was never really meant as a diagnostic tool for conditions like obesity which rely on several different factors. For instance, take a football player of short stature. They are likely to have a lot of muscle relative to their height. That would give them a higher than average BMI because BMI only looks at mass to height ratio and, if you were to look only at that BMI score, you may class the person as perhaps even dangerously overweight. If we take bodybuilders, who push their physiques to even greater extremes but who may have very little body fat, we might see the calculation pushing into the obese category.
So what is this research picking up on? One theory is that the BMI-cancer link relates to the known correlation between cancer risk and visceral fat, that is the amount of fat we store around the trunk of our bodies and in particular near our internal organs. We know, for instance, that there’s a positive correlation between higher visceral fat levels and greater breast cancer and prostate cancer risk. A higher BMI score may indicate the likelihood of higher visceral fat levels and in turn an increased cancer risk. That’s not to mention the extreme stress being overweight can put our bodies under, which in turn may raise our cancer risk.
Another theory (which may in fact link to visceral fat levels) is that obesity changes the hormonal landscape in the body, creating excesses of key hormones like estrogen. We already know that excess hormone levels are a cancer risk, and so it’s possible that the BMI-cancer relationship is indicative of just such a problem.
All that said, the exact causation here will need to be determined with future studies, but this does fit quite neatly into what we already know about the obesity and cancer risk link.
For practical purposes in the short term, this study illustrates the need to redouble our efforts to lower obesity rates not just for the fact of all the health complaints obesity itself is known to cause, but as a future cancer-fighting plan, too. As such, when we talk about how we need to combat cancer, it may well benefit us to stress immediate short term health goals and really emphasize diet and exercise as key cancer fighters.
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