The results of the study are published in the November issue of Cancer Epidemiology, Biomarkers and Prevention journal.
Other studies have shown overweight and obesity are risk factors for colon, breast, kidney and endometrial cancers. This study, sponsored by the National Cancer Institute, examined the potential link between obesity and risk of leukemia. Over 14 years, the health of more than 37,000 older Iowa women was monitored; 200 of the women developed leukemia - 74 were diagnosed with AML and 88 with chronic lymphocytic leukemia (CLL).
"We found that the risk for getting AML was 90 percent higher in overweight women age 55 and older who had a body mass index (BMI*) of 25-29," says Julie Ross, Ph.D., associate professor of pediatrics at the University of Minnesota Medical School. She also is an epidemiologist at the University of Minnesota Cancer Center and the lead researcher on this study. "In obese women age 55 and older and with a BMI of 30 or greater, the risk increased to as much as a 140 percent."
The study found little evidence of an association between overweight and obesity with CLL.
AML is cancer that starts in the bone marrow in immature cells that normally should become white blood cells. Acute means the leukemia develops quickly.
According to the American Cancer Society, about 33,400 new cases of leukemia will be diagnosed in the United Sates this year. About half of those cases will be acute leukemias. AML is the most common acute leukemia with about 11,900 patients diagnosed annually; 90 percent of them adults age 65 and older. About 8,870 people with AML will die this year. The 5-year survival rate for middle-aged people is about 12 percent and 3 percent for elderly adults.
While incidence rates for some adult leukemias, such as CLL and chronic myeloid leukemia, are declining in the United States, AML in people over age 65 has increased about 10 percent in the last 25 years.
"The fact that survival rates for AML are extremely poor for older individuals makes identifying people who are at increased risk for this cancer of public health importance," Ross says. "Given that about 65 percent of adults in the United States are overweight or obese, the projection we can make from our study is that about 30 percent of AML in older adult women could be due to being overweight or obese."
This study is part of the Iowa Women's Health Study. In 1986, over 40,000 women between the ages of 55 and 69 years completed a lifestyle and health questionnaire that included current height and weight. This study followed more than 37,000 of these women who, with the possible exception of skin cancer, were cancer-free at the beginning of the study.
"The risk of AML was increased among women who reported being overweight or obese compared with women of normal weight," Ross says. We don't know why higher BMI would be associated with leukemia, particularly AML. A possible explanation could be an alteration in hormones linked with obesity."
She adds that while it can't be said with research certainty, "it would seem that as with other cancers linked to obesity, reducing excess pounds and maintaining normal weight would be important in preventing AML."
Ross says a limitation of her study was that only postmenopausal, mostly white, women participated. She also says BMI was calculated using weight and height reported by each participant, which could be subject to some degree of imprecision. However, she notes, BMI is the standard for population-based studies.
The Cancer Center at the University of Minnesota is a National Cancer Institute-designated Comprehensive Cancer Center. The Cancer Center conducts cancer research that advances knowledge and enhances care. The center also engages community outreach and public education efforts addressing cancer. To learn more about cancer, visit the University of Minnesota Cancer Center Web site at http://www.
* BMI is the measure of body fat based on height and weight; it is the standard used for population-based research studies on obesity. As an example, a 5'4" woman would be considered overweight if she weighed between 146 and 174 pounds, and obese if she weighed 175 pounds or more. To calculate body mass index, visit the National Institutes of Health at http://nhlbisupport.