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Higher BMI increased risk for 10 common cancers
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Higher BMI increased individuals’ risks for 10 common cancers, according to results of a population-based cohort study conducted in the United Kingdom.
More than 12,000 cases of these malignancies each year in the UK can be attributed to patients being overweight or obese, and nearly 4,000 more of these cancers could occur each year if the average BMI of the country’s population continues to increase, results showed.
“The number of people who are overweight or obese is rapidly increasing, both in the UK and worldwide,” researcher Krishnan Bhaskaran, PhD, a National Institute for Health Research postdoctoral fellow at London School of Hygiene & Tropical Medicine, said in a press release. “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.”
Bhaskaran and colleagues collected data from the UK Clinical Practice Research Datalink, which contains primary care records from about 9% of the country’s population. Researchers used the data — which include information about specialist referrals, hospital admissions and diagnoses made in secondary care — to assess the associations between BMI and 22 common cancers.
Data collection began in 1987 and continued through July 2012. Follow-up continued from study entry until the earliest of four time points: first cancer diagnosis, death, transfer out of the Clinical Practice Research Datalink, or the last data collection date for the practice.
The analysis included 5.24 million individuals, of whom 166,955 developed one of the 22 cancer types of interest.
Results showed each 5 kg/m2 increase in BMI was associated with increased risks for uterine cancer (HR=1.62; 99% CI, 1.56-1.69), gallbladder cancer (HR=1.31; 99% CI, 1.12-1.52), kidney cancer (HR=1.25; 99% CI, 1.17-1.33), cervix cancer (HR=1.1; 99% CI, 1.03-1.17), thyroid cancer (HR=1.09; 99% CI, 1-1.19) and leukemia (HR=1.09; 99% CI, 1.05-1.13).
Results also showed higher BMI increased overall risks for liver cancer (HR=1.19; 99% CI, 1.12-1.27), colon cancer (HR=1.1; 99% CI, 1.07-1.13), ovarian cancer (HR=1.09; 99% CI, 1.04-1.14) and postmenopausal breast cancer (HR=1.05; 99% CI, 1.03-1.07). However, underlying BMI and other individual characteristics — such as gender and menopausal status — influenced those associations.
Based on their results, if causality is assumed, researchers determined 41% of uterine cancers and at least 10% of colon, gallbladder, kidney and liver cancers could be attributed to excess weight.
“Even within normal BMI ranges, higher BMI was associated with increased risk of some cancers, accentuating the public health implications in view of the overall increase in population BMI distributions in several countries,” Bhaskaran and colleagues wrote.
Bhaskaran and colleagues observed inverse associations between higher BMI and risk for prostate and premenopausal breast cancers. The associations were apparent among the overall cohort (prostate cancer, HR=0.98; 99% CI, 0.95-1; premenopausal breast cancer, HR=0.89; 99% CI, 0.86-0.92) and among never-smokers (prostate cancer, HR=0.96; 99% CI, 0.93-0.99; premenopausal breast cancer, HR=0.89; 99% CI, 0.85-0.94).
“There was a lot of variation in the effects of BMI on different cancers,” Bhaskaran said. “Risk of cancer of the uterus increased substantially at higher BMI. For other cancers, we saw more modest increases in risk or no effect at all. For some cancers, like breast cancer occurring in younger women before menopause, there even seemed to be a lower risk at higher BMI. This variation tells us that BMI must affect cancer risk through a number of different processes, depending on the cancer type.”
A review of data from 2003 through 2010 showed mean BMI in England has increased at a rate equivalent to 1 kg/m2 every 12 years. Based on current BMI rates, a 1 kg/m2 population-wide increase in the country — the equivalent of 8 to 10 pounds per adult — could lead to another 3,790 total annual cases of the 10 cancer types shown to be positively associated with BMI, researchers concluded.
“Our data strengthen the rationale to assess and implement strategies aimed at stopping these trends and mitigating their public health effects,” Bhaskaran and colleagues wrote.
Despite the findings, the volume of evidence suggesting obesity is a key cause of “unnecessary suffering and death from many forms of cancer” already is sufficient, Peter Campbell, PhD, who directs the tumor repository in the epidemiology research program at the American Cancer Society, wrote in an accompanying comment.
“More research is not needed to justify, or even demand, policy changes aimed at curbing overweight and obesity,” Campbell wrote. “Research strategies that identify population-wide or community-based interventions and policies that effectively reduce overweight and obesity should be particularly encouraged and supported. Moreover, we need a political environment, and politicians with sufficient courage, to implement such policies effectively.”
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Derek M. Huffman, PhD
Many of the results that I saw in this study look to be things that we’ve already had a general idea were the case for the past two decades. Although it was not necessarily ground-breaking, it was powerful to see that many of trends shown previously were confirmed in a large population in the UK.
It does confirm the risk for developing a wide range of cancers — it’s not limited in scope to just a couple. Obesity really does not discriminate among the majority of these cancers. It is truly increasing the risk for developing most forms of this disease, albeit some more than others.
What is not in this study — which may be just as relevant, if not more so — is that once you have cancer, if you’re obese, you have an even greater risk of dying from it. It’s that connection that’s really the most potent of all. Obesity is an important cause of morbidity in terms of cancer.
In this study, obesity was linked to a 10% risk for colon cancer. If you look at the literature that links obesity with colon cancer mortality, that risk can be almost twofold in men. So, the effects are quite clear and once you have the disease, obesity becomes an even more problematic condition.
It’s a really important point to make with patients who have obesity, especially if there’s a family history of cancers. Many patients are aware that if they’re obese, there is a good probability they will have to be treated for metabolic diseases. They’re going to have to take care of cholesterol. They’re going to have to take care of high blood pressure or high blood sugar. Those are all things of which most of the lay public are quite aware.
The link between excess weight and cancer is something not many people realize. You tend to get a lot of surprised looks when you tell people that being obese does increase their risk for cancer, too.
Truly, what this study is really hammering home (that we already know) is when you’re overweight and obese, you’re not only increasing your risk for some things, you’re increasing the risk for most all of the major age-related diseases that are out there.
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