Obesity increases the risk of developing multiple myeloma, according to an article in the July issue of Cancer Epidemiology, Biomarkers & Prevention.

Researchers, who analyzed data from more than 100,000 adults in the ongoing Nurses’ Health Study and Health Professionals Follow-up Study, found that Body Mass Index (BMI) - a statistical measure that scales weight to height - provides an indicator for risk of developing multiple myeloma. Multiple myeloma currently affects more than 50,000 people in the USA, and the five-year survival rates are below 40 percent.

The current findings are similar to those from previously published studies that included smaller numbers of multiple myeloma patients and/or were based on one-time recording of height and weight.

“I find the results of these studies encouraging, since they show consistent results about the first risk factor for multiple myeloma that people can actually modify,” said lead author Brenda M. Birmann, ScD, of the Department of Medicine at Brigham and Women’s Hospital and Harvard Medical School. “Treatment options for this disease are improving, but it is also important to identify risk factors that could be modified. We would like to learn how to prevent its occurrence.”

The Brigham and Women’s Hospital-based Nurses’ Health Study has followed the health of female registered nurses since 1976, and the Health Professionals Follow-up Study, based at Harvard School of Public Health, has followed men from several health professions since 1986. These studies recorded height, weight and physical activity for each person enrolled, as well as diet, medications, smoking habits and other health behaviors, and have updated that information every two to four years. Of the 136,623 participants who qualified for their study protocol, Birmann and her colleagues confirmed 215 cases of multiple myeloma.

Body Mass Index (BMI) is computed by dividing a person’s weight by the square of their height. A BMI between 18.5 and 25 is considered optimal, a BMI of 25-29 is considered overweight, and a BMI of 30 or higher is considered obese.

The association between BMI and multiple myeloma was strongest among men with a BMI of 30 or more. When compared with leaner men (those with a BMI below 22), obese men were over twice as likely to develop multiple myeloma. The effect was less pronounced among overweight or obese women, although women also had an increased risk.

The study also examined whether regular exercise is related to risk of multiple myeloma. There was no clear effect of exercise on risk, although the results among women suggested that those who exercise more might have a lower risk. “We cannot say with certainty that exercise reduces the risk of multiple myeloma, but there is ample evidence that regular exercise offers many other health benefits,” Birmann said.

The study findings do show, however, that the effect of BMI on risk of multiple myeloma is separate from any possible effect of physical activity.

According to Birmann, previous research has identified possible biological links between obesity and multiple myeloma. For example, adipocytes produce interleukin-6 (IL-6), which promotes an inflammatory response. In obese people, this can cause an overproduction of IL-6, which in turn creates a cellular environment that sustains multiple myeloma.

“The IL-6 chemical pathway is one possible way obesity could influence the risk of developing diseases like cancer or cardiovascular disease, but the answer might also lie in other relationships between obesity and cancer,” Birmann said.