September 15, 2010 — Evidence suggests a link between obesity and an increased risk for colon cancer. But there is also evidence that obesity increases the risk of dying from colon cancer after the disease is diagnosed.
Results from a study published in the September issue of Cancer Epidemiology, Biomarkers & Prevention provide evidence that "obesity is not only a risk factor for colon cancer incidence, but it may also increase mortality of postmenopausal women after colon cancer diagnosis," the researchers conclude.
In addition, they note that "our findings suggest that abdominal obesity is more predictive of mortality from colon cancer than is general obesity."
Women with the highest waist-to-hip ratio (WHR), which reflects abdominal obesity, had a 30% to 40% greater risk of dying from colon cancer than women with the lowest WHR.
Women who were classified as obese, defined by a body mass index (BMI) of at least 30 kg/m2, had a 45% increased overall mortality rate.
Interestingly, being underweight was also an indicator of worse survival. Although only a small number of women in the study cohort met the parameters for being underweight, defined as a BMI of less than 18.5 kg/m2, they had an 89% increased mortality rate, compared with those of normal weight.
"Maintaining a healthy body weight is beneficial for postmenopausal women," said lead author Anna E. Prizment, PhD, MPH, a postdoctoral fellow in the Division of Epidemiology and Community Health at the University of Minnesota in Minneapolis, in a statement.
Abdominal obesity might be a useful indicator of higher colon cancer mortality, noted Dr. Prizment. Currently, it's too early to tell if losing weight after being diagnosed with colon cancer will decrease the mortality risk.
"At that point it may be too late," she said. "Therefore, it's best to maintain a normal, healthy body weight throughout life."
Convincing Evidence in the Literature
As previously reported by Medscape Medical News, there is convincing evidence that excess weight and obesity can increase the risk for colon cancer, as well as for several other cancers. Other research has pointed to a positive association between a higher BMI and all-cancer mortality. This relation was particularly pronounced for cancers of the colon, breast (in women 60 years or older), ovary, cervix, and prostate, and for leukemia.
In the current study, the authors note that even though previous research has clearly established a link between obesity and a higher incidence of colon cancer, and that obese people are more likely to die from the disease, "little is known about how prediagnostic obesity affects survival in patients newly diagnosed with colon cancer."
Dr. Prizment and colleagues hypothesized that increased measures of body size at baseline, including weight, waist circumference, WHR, and BMI, would be associated with a poorer prognosis among postmenopausal colon cancer patients.
Excess Weight Independent Predictor of Survival
The authors used data from the Iowa Women's Health Study, which examined 1096 women who were diagnosed with colon cancer from 1986 to 2005. During the 20-year follow-up period, 493 participants died; 289 of these deaths were related to colon cancer.
In this cohort, 38.1% of the women were overweight, 26.9% were obese, and approximately 1.3% were underweight prior to their diagnosis of colon cancer. Compared with the entire cohort, the proportion of overweight/obese women who developed colon cancer was slightly higher (65.0% vs 60.4%).
After controlling for age at diagnosis, education, smoking status, pack-years of smoking, and stage of colon cancer at diagnosis, a multivariate analysis showed that all-cause mortality was associated positively with weight, WHR, and waist circumference. The hazard ratios (HRs) were increased by 36% to 45% for the highest vs the lowest tertiles.
Compared with women with a BMI of 18.5 to 24.9 kg/m2, HR was 1.45 (95% confidence interval [CI], 1.14 - 1.85) for obese women (BMI ≥30 kg/m2) and 1.89 (95% CI, 1.01 - 3.53) for the few underweight women (BMI <18.5 kg/m2). These associations, the authors note, did not substantively change after adjustment for diabetes and heart disease, or after adjustment for the first course of treatment.
When the data were analyzed for colon-cancer-specific mortality, the authors observed positive trends for weight, WHR, and waist circumference. But in contrast to what was observed for all-cause mortality, only waist (HR, 1.34; 95% CI, 1.01 - 1.80; P trend = .05) and WHR (HR, 1.37; 95% CI, 1.02 - 1.85; P trend = .04) were statistically significant associations for colon cancer.
The study was supported by a grant from the National Institute of Cancer. The authors have disclosed no relevant financial relationships.
Cancer Epidemiol Biomarkers Prev. 2010;19:2229-2237. Abstract
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Cite this: Obesity Increases Colon Cancer Mortality - Medscape - Sep 15, 2010.
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