Multiple myeloma is currently an incurable blood cancer that occurs when white blood cells called plasma cells form cancerous tumors in the bone marrow.
It is the second most commonly diagnosed blood cancer after non-Hodgkin lymphoma. Findings from a study published earlier this year in the British Journal of Cancer suggest that having a high body mass index in young adulthood or later in life may increase the risk of developing multiple myeloma.
“Since there is no cure for multiple myeloma, an emphasis on prevention and identifying risk factors to stop it from developing is important,” says Catherine Marinac, Ph.D., a Postdoctoral Fellow at the Dana-Farber Cancer Institute and Harvard TH Chan School of Public Health and one of the co-authors of the study.
Marinac and her colleague, Brenda Birmann, ScD, an Associate Epidemiologist and Assistant Professor of Medicine at Brigham and Women’s Hospital and Harvard Medical School, wanted to determine if body mass index – a proxy for body fatness – influences a person’s risk for developing multiple myeloma. “Obesity is currently the only modifiable risk factor associated with multiple myeloma risk,” says Marinac.
The study was conducted using data from three prospective cohort studies – the Nurses’ Health Study, the Health Professionals Follow-up Study, and the Women’s Health Study. Approximately 50,000 men and 154,000 women, whose average ages ranged between 48 and 55 years at enrollment, participated in the study. The follow-up period was 26 years for the men and up to 36 years for the women.
Participants completed questionnaires at the time of enrollment and at approximately two-year intervals, in which they provided information about their height, body weight as young adults, current body weight, physical activity level, and health status, including cancer diagnosis.
Based on the information provided in the questionnaires, the researchers determined the participants’ BMI at multiple timepoints in their adult lives. A person’s BMI is calculated by dividing their body weight in kilograms (kg) by their height in meters, squared (m2).
Although previous studies have investigated associations between adult BMI and risk of multiple myeloma, Marinac and Birmann also considered the influence of young adult BMI. “We wanted to determine whether an early-life exposure such as obesity would have an association with risk for myeloma,” says Birmann.
The researchers classified the participants’ BMIs into one of five categories: less than 23, 23 to less than 25, 25 to less than 27.5, 27.5 to less than 30, or greater than or equal to 30. A person whose BMI is 30 or greater is considered to have obesity. They also looked at whether the participants’ BMI changed – indicating that they had lost or gained weight – throughout adulthood.
A final component of the researchers’ analysis involved assessing the participants’ physical activity. “We know that physical activity is associated with BMI, and we thought that physical activity might counter some of the negative effects of obesity,” says Marinac. They calculated a summary measure of the participants’ weekly physical activity and walking using metabolic equivalents, which gauge exercise intensity based on known measures of oxygen consumption. They identified four levels of activity and walking, ranging from none to high.
Participant reports of multiple myeloma diagnoses were confirmed with medical records, tumor registries, death records, or other means.
Statistical analysis revealed that the participants were mostly white males and females. Their average BMI ranged from 23.8 to 25.8 at the time of enrollment, and from 21.3 to 23.0 in young adulthood. During the three study periods, 575 participants developed multiple myeloma.
The study yielded surprising results regarding physical activity. “Contrary to our hypothesis, we didn’t see an association between physical activity or walking and risk of multiple myeloma,” says Marinac. “This lack of association may be because the participants reported their own activities. Self-reporting is often an imprecise measure of physical activity,” says Marinac.
The findings from this study suggest that BMI influences a person’s risk of developing multiple myeloma. “We learned that young adult BMI is as important – if not more important – than later adult BMI,” says Birmann. “This lends additional support to public health messages and adds to the benefits that people can enjoy by maintaining a healthy weight throughout life.”
The strengths of this study include its prospective design and a large number of participants. One notable weakness, however, is the lack of social and demographic diversity among the participants, which makes generalizing the findings across other populations difficult.
Marinac, Catherine R., et al. “Body mass index throughout adulthood, physical activity, and risk of multiple myeloma: a prospective analysis in three large cohorts.” British journal of cancer 118.7 (2018): 1013.
Cancer Stat Facts: Myeloma, National Cancer Institute, accessed November 1, 2018.