Colon Cancer May be Preventable in the Overweight

Overweight and obesity is a global health concern. In the US, more than 69% of adults aged 20 years or over are overweight or obese. Similar numbers are found in the UK, where around 62% of individuals aged 16 or over are overweight or obese.

It is well known that being overweight can increase the risk of potentially serious health problems, such as diabetes, heart disease, high blood pressure and stroke. Past research has also suggested that overweight and obesity can increase the risk of cancer.

Now, researchers led by Dr. Krishnan Bhaskaran, of the London School of Hygiene & Tropical Medicine in the UK, have conducted what they say is the largest study of its kind to assess the link between body mass index (BMI) and cancer.

Effects of BMI on cancer varied

To reach their findings, the team assessed data from general practitioner records found in the UK’s Clinical Practice Research Datalink (CPRD).

From this, they identified 5.24 million people aged 16 or over who were free of cancer and had been monitored for an average of 7.5 years.

The team analyzed participants’ BMI and calculated their risk of developing 22 of the most common cancers, which they say accounts for 90% of all cancers diagnosed in the UK.

Results of the analysis revealed that 166,955 participants developed one of the 22 cancers during the 7.5-year follow-up. The researchers found that BMI was linked to the development of 17 out of these 22 cancers, and the link was particularly strong for 10 of these cancers.

Fast facts about obesity in the US

• Around 76.8 million adults in the US are obese
• Obesity has more than doubled in children and quadrupled in adolescents over the past 3 decades
• In 2008, the medical costs for people who were obese were $1,429 higher than those of normal weight.

They found that every 5 kg/m² increase in BMI was associated with a higher risk of the following cancers:

• Womb (62% increased risk)
• Gallbladder (31% increased risk)
• Kidney (25% increased risk)
• Cervical (10% increased risk)
• Thyroid (9% increased risk)
• Leukemia (9% increased risk).

The researchers also found that high BMI was associated with a 19% higher risk of liver cancer, a 10% higher risk of colon cancer, a 9% higher risk of ovarian cancer and a 5% increased risk of breast cancer.

The team notes that all increased risks varied dependent on underlying BMI and individual’s sex and menopausal status, and that they did find some evidence that high BMI was associated with a lower risk of prostate and premenopausal breast cancer.

“There was a lot of variation in the effects of BMI on different cancers,” explains Dr. Bhaskaran.

“For example, risk of cancer of the uterus increased substantially at higher body mass index; 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 the 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.”

Continued increase in BMI could cause up to 3,800 additional cancer cases annually

From their findings, the team calculated that overweight or obesity may account for 41% of womb cancers in the UK and more than 10% of all gallbladder, kidney, liver and colon cancers.

Furthermore, they believe that a 1 kg/m² increase in average BMI (the equivalent to 8-10 pounds per adult) across the UK population – which they say would occur around every 12 years based on current trends – may cause an additional 3,790 cases of the 10 cancers every year.

Commenting on these estimates, Dr. Bhaskaran says:

“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.”

In an editorial linked to the study, Dr. Peter Campbell, of the American Cancer Society, notes there is “sufficient evidence” that overweight and obesity is a cause of cancer, and “more research is not needed to justify, or even demand, policy changes aimed at curbing overweight and obesity.”

“Some of these policy strategies have been enumerated recently, all of which focus on reducing caloric intake or increasing physical activity, and include taxes on calorically dense, nutritionally sparse foods (e.g., sugar-sweetened beverages), subsidies for healthier foods, especially in economically disadvantaged groups, agricultural policy changes and urban planning aimed at encouraging walking and other modes of physical activity,” he adds.

“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.”