Obesity Linked to Increased Cancer Mortality Risk in Asia/Pacific Region

Roxanne Nelson

July 02, 2010

July 2, 2010 — Persons living in the Asia-Pacific region who are overweight and obese have a significantly increased risk for mortality from cancer compared with the risk for individuals of normal weight, according to a new report published online June 30 in Lancet Oncology.

Among individuals with a body mass index (BMI) higher than 18.5 kg/m2, the authors found that there was "a positive and continuous association between BMI and all-cancer mortality." Compared with persons with a normal weight, the relative risk for cancer-related mortality was 1.06 (95% confidence interval [CI], 1.00 - 1.12) for those who were overweight and 1.21 (95% CI, 1.09 - 1.36) among obese persons.

In addition, the positive association noted between BMI and all-cancer mortality was particularly pronounced for colon cancer, breast cancer (in women 60 years or older), ovarian cancer, cervical cancer, prostate cancer, and leukemia.

These results have clear implications for health policy, notes Andrew G. Renehan, PhD, FRCS, FDS, from the Department of Surgery, School of Cancer Studies, University of Manchester, United Kingdom, in an accompanying editorial.

Although the mean BMI values have increased in many North American and European populations during the past 30 years, those for Asian populations have generally lagged behind, explains Dr. Renehan.

"However, with a large denominator for all-site cancers in the Asia-Pacific region (6.2 million vs 3.4 million for Europe and 1.6 million for North America), the population impact number (ie, numbers of cases attributable to excess bodyweight) might be substantial," he writes.

Dr. Renehan also points out that although the present study data are helpful in comparing risks between 2 different populations (Asian vs Australian and New Zealand), the study "does not account for where in the BMI distribution the effects of excess weight start to increase.

"Thus, many Asian populations have increased risk for type 2 diabetes and cardiovascular disease at BMIs lower than the [World Health Organization] cutoff," he writes. "If this is the case for cancer risk, then the number of cancers attributable to excess weight in Asians might be even greater."

Higher Risk for Mortality

In this study, Christine L. Parr, PhD, from the Institute of Basic Medical Sciences at the University of Oslo, Norway, and colleagues evaluated the association of BMI with cancer mortality (overall and for 20 cancer sites) in diverse populations from Asia and from Australia and New Zealand, within the Asia-Pacific Cohort Studies Collaboration (APCSC). The APCSC is a large, collaborative data-pooling project that involves data from more than 600,000 participants in the Asia-Pacific region.

The pooled data came from 39 cohorts, with a total of 424,519 people. Of this group, 326,387 (77%) were from Asian cohorts and 175,364 (41%) were women. The mean age was 48 years, and median follow-up was 4 years.

During the follow-up period, there were 7211 cancer-related deaths, of which 4130 (57%) occurred in the Asian cohorts. The authors noted that overall, the most common cancer site was lung (20%, n = 1478), followed by stomach (12%, n = 855), liver (11%, n = 774), and large intestine (9%, n = 668). The distribution of cancers varied by sex and region.

Participants with less than 3 years of follow-up were excluded, leaving a total of 4872 cancer deaths in 401,215 individuals. After adjustment for age and smoking status, the researchers noted an increased risk for mortality in both the underweight (BMI, <18.5 kg/m2; hazard ratio, 1.13; 95% CI, 1.00 - 1.28) and obese (BMI, ≥30 kg/m2; hazard ratio, 1.11; 95% CI, 1.00 - 1.23) categories compared with the normal-weight control participants (BMI, 18.5 - 24.9 kg/m2).

When looking at all cancer sites, the increased risk for death in mortality risk in obese (BMI, ≥30 kg/m2) persons compared with those of normal weight (BMI, 18.5 - 24.9 kg/m2) was 1.21 (95% CI, 1.09 - 1.36), excluding lung and upper aerodigestive tract cancers. For specific cancer sites, it was:

  • 1.50 (95% CI, 1.13 - 1.99) for colon,

  • 1.68 (95% CI, 1.06 - 2.67) for rectum,

  • 1.63 (95% CI, 1.13 - 2.35) for breast in women 60 years or older,

  • 2.62 (95% CI, 1.57 - 4.37) for ovary,

  • 4.21 (95% CI, 1.89 - 9.39) for cervix,

  • 1.45 (95% CI, 0.97 - 2.19) for prostate, and

  • 1.66 (95% CI, 1.03 - 2.68) for leukemia at 3 years after left censoring (exclusion of study participants with follow-up time less than a certain duration).

The authors did not observe any clear associations between BMI and other types of cancer, including that of the esophagus, stomach, liver, pancreas, melanoma (skin), bladder, kidney, uterus, brain and nervous system, lymphoma, myeloma, or all hematological cancers combined.

There was also little evidence of a regional difference among Asia and Australia/New Zealand in the association between a high BMI and cancer.

Preventive Strategies Needed

The authors note that many countries of the Asia-Pacific region are showing a sharp rise in the numbers of overweight and obese individuals, primarily as a result of a shift from traditional to more Western lifestyles. "Effective strategies to prevent the increasing proportions of overweight and obese people in Asian populations need to be developed and assessed to reduce the burden of cancer that can be expected if the obesity epidemic continues," they write.

"However, this study does not show a higher relative risk for cancer mortality in Asian populations compared with Western populations for the same level of BMI, as has been suggested for diabetes and cardiovascular disease," they conclude.

The authors have disclosed no relevant financial relationships. Dr. Renehan has served on the advisory board of and received research support from Novo Nordisk. The study was funded by National Health and Medical Research Council of Australia, Health Research Council of New Zealand, and Pfizer Inc.

Lancet Oncol. Published online June 30, 2010.

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