Substantially Increased Risk for Cancer With Higher BMI

Pam Harrison

August 14, 2014

A higher body mass index (BMI) substantially increases the risk for the majority of cancers diagnosed in the United Kingdom, the largest study of its kind on BMI and cancer suggests. The study was published online August 14 in the Lancet.

"We know from smaller studies that body weight is importantly related to the risk of developing some types of cancer," said Krishnan Bhaskaran, PhD, from the National Institute for Health Research, London School of Hygiene & Tropical Medicine, in the United Kingdom.

"But what we really wanted to do with this study was find out how large these effects are, how they vary across a wide range of cancers, and what the real impact of body weight is at a population level. We found that BMI was associated with the majority of cancers that we looked at and, for 10 of the most common cancers, higher BMI was very clearly associated with higher risk," he told Medscape Medical News.

"There was a lot of variation in the effects of BMI on different cancers," he noted. However, the greatest effect was on cancer of the uterus. After adjustment for all potential confounders, each 5 kg/m² increase in BMI (15.5 kg) was associated with a 62% increase in the risk for uterine cancer (hazard ratio [HR], 1.62), the researchers report.

"For a woman of average height, our estimates suggest that a 2-stone [12.7 kg] increase in weight would increase the risk of uterine cancer by over 60%," Dr. Bhaskaran explained.

"We estimate that this effect is responsible for over 3000 cases of uterine cancer a year in the United Kingdom," he said.

Study of More Than 5 Million People

Using data from general practitioner records in the Clinical Practice Research Datalink, the researchers identified 5.24 million people 16 years of age and older who were free of cancer at the time of assessment. BMI was calculated directly from weight and height records. Participants were followed for a mean of 7.5 years after the first eligible BMI measurement. Mean BMI was 25.5 kg/m².

In the cohort, 166,955 people developed 1 of the 22 cancers evaluated during the follow-up period. The 22 cancers of interest represent 90% of all cancers diagnosed in the United Kingdom.

The researchers found that BMI was associated with 17 of the 22 cancers.

There were large weight-related increases in risk for cancers of the gallbladder, kidney, and liver, and smaller increases in the risk for colon, cervical, thyroid, ovarian, and postmenopausal breast cancer, and for leukemia.

Even though the effect of a higher BMI on common cancers, such as colon and postmenopausal breast cancer, were more modest, "these are very common cancers," Dr. Bhaskaran noted, "so the number of cases due to excess weight would be just as large [as for uterine cancer]."

In contrast, there was some indication that a high BMI was associated with a slightly lower risk for premenopausal breast cancer and prostate cancer.

Table. Increase in the Risk for Cancer With Every 5 kg/m² Increase in BMI

Type of Cancer Percent Increase
Uterus 62
Gallbladder 31
Kidney 25
Liver 19
Cervix 10
Colon 10
Thyroid 9
Leukemia 9
Ovarian 9
Postmenopausal breast 5

 

"We already know we need to tackle obesity because it has effects on cardiovascular disease and diabetes," Dr. Bhaskaran said. "This study confirms the effect to which obesity is important for cancer as well."

Because the problem of obesity is multifactorial, multifactorial solutions are required. These include raising awareness about offending foods, which are usually cheap and widely available, and modifying the environment to promote physical activity as part of our daily lives, he noted.

Results Are "Largely Confirmatory"

The results of this study are "largely confirmatory," said Peter Campbell, PhD, from the epidemiology research program at the American Cancer Society. "Nothing about the study jumped out as being awkward or potentially erroneous," he told Medscape Medical News.

 
Obesity is a certain and avoidable cause of cancer.
 

"The overall message is that obesity is a certain and avoidable cause of cancer," Dr. Campbell said. This is not news, but "the study adds further evidence that the association is essentially definitive." In terms of obesity being avoidable, he acknowledged, that's a much more challenging issue.

There is some evidence in the United States that the prevalence of obesity has at least plateaued. "There isn't much evidence of the prevalence dropping over time, but at least it hasn't been getting worse over the last 10 years or so. So I think there some hope in this," he said.

Dr. Campbell emphasized that more research is not needed to justify or even demand policy changes aimed at curbing the problem of excess weight, and that governments need to take measures to reduce caloric intake and increase physical activity by whatever policy means are at their disposal.

This study was funded by the National Institute for Health Research, Wellcome Trust, and the Medical Research Council. Dr. Bhaskaran and Dr. Campbell have disclosed no relevant financial relationships.

Lancet. Published online August 14, 2014. Abstract

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