An inter­na­tional team of researchers recently found that people with MGUS who consumed fruit at least three times a week had a lower risk of pro­gress­ing to multiple myeloma than people with MGUS who consumed fruit less frequently.

The impact of higher fruit consumption on risk of pro­gres­sion was sizable. The statistical models developed by the researchers indicate that eating fruit three times or more each week cut the risk of pro­gres­sion by at least a half.

The researchers also found that the risk of devel­op­ing MGUS was about 35 per­cent lower in people who consumed fruit at least three times a week during ado­les­cence, and 20-25 per­cent lower in people who ate whole wheat bread at least five times a week in midlife.

Consumption of other food groups in either ado­les­cence or midlife did not have a statistically sig­nif­i­cant impact on the risk of devel­op­ing MGUS.

MGUS And Multiple Myeloma

MGUS, or "monoclonal gam­mop­athy of undetermined sig­nif­i­cance," is a disorder similar to multiple myeloma in that both con­di­tions involve the presence of ab­nor­mal (“clonal”) plasma cells in the body. These dysfunctional plasma cells typically produce either mono­clonal immuno­glob­u­lins, excess kappa or lambda free light chains, or both.

Everyone who has multiple myeloma has had MGUS at some point in the past, even if they were never diag­nosed with the disease. Someone who has MGUS, on the other hand, will not automatically progress to having multiple myeloma at some later date. Indeed, the risk of MGUS progressing to multiple myeloma or a related disorder is only about 1 per­cent per year.

Interpretation Of Study Results

In their article summarizing the results of their study investigating diet, MGUS, and pro­gres­sion to multiple myeloma, the authors write that their findings are in line with pre­vi­ous research, which has shown that eating a diet rich in plant-based food tends to reduce the risk of devel­op­ing cancer.

However, the authors recog­nize that there may be alter­na­tive explanations for some of their results. For example, their study was carried out using data for people in Iceland who were born prior to World War II. Among these individuals, fruit con­sump­tion during ado­les­cence may have been more common in families with a higher socio­eco­nomic status, and pre­vi­ous research has found that higher socio­eco­nomic status in and of itself is asso­ci­ated with a lower risk of multiple myeloma.

The researchers did not observe an association between high fish intake and the risk of devel­op­ing MGUS or the risk of MGUS progressing to multiple myeloma. This came as a bit of a surprise to the authors, as some studies have suggested that fish consumption may lower a person's risk of devel­op­ing multiple myeloma. The authors speculate that their finding may be due to the fact that fish consumption is high for all residents in Iceland, and they did not have a control group in their study which did not consume fish.

Nevertheless, based on their findings, the researchers believe that diet may affect a person's risk of devel­op­ing MGUS and the risk of MGUS progressing to multiple myeloma.

Study Design And Additional Results

The new study makes use of data from the Age, Gene/Environment Susceptibility-Reykjavik ("AGES") Study. The AGES study in­cluded 5,764 individuals from the Reykjavik metropolitan area who were born between 1907 and 1935 and who were ran­domly chosen to par­tic­i­pate in the study based on their par­tic­i­pa­tion in a precursor study, known as the Reykjavik Study, which started in 1967.

The mean age of the AGES study participants was 77 years old at study entry; 5.2 per­cent of the patients had MGUS accompanied by a serum M-spike at study entry, and 4.8 per­cent had light chain-only MGUS at study entry.

During a median follow-up time of eight years, 3.1 per­cent of the all study participants with MGUS had progressed to active multiple myeloma, and 5.1 per­cent had progressed to either multiple myeloma or another lymphoproliferative disease, such as Hodgkin's or non-Hodgkin's lym­phoma, Waldenström's macroglobulinemia, or acute or chronic lym­pho­cytic leukemia. (Lymphoproliferative diseases occur when the body overproduces white blood cells known as lym­pho­cytes.)

Progression to either multiple myeloma or another lymphoproliferative disease occurred primarily in patients with non light chain MGUS (that is, MGUS with a serum M-spike); 8.7 per­cent of non light chain MGUS patients progressed, compared to 1.1 per­cent of the light chain MGUS patients. (For more in­for­ma­tion on the risk of pro­gres­sion in light chain MGUS, see this Beacon news article).

The AGES study participants provided in­for­ma­tion about their dietary habits via answers to a ques­tion­naire. They were asked questions about their diet during three periods of their lives: adolescence (14 to 19 years old), midlife (40 to 50 years old), and late life. The questions covered the intake of certain foods and food groups, such as fish, meat, milk and milk prod­ucts, fruit, vegetables, whole wheat bread, and oatmeal.

Data from the AGES study was linked with data in the nationwide Icelandic Cancer Registry to determine which AGES study participants developed multiple myeloma or some other lymphoproliferative diseases.

For more in­for­ma­tion, please see the study by Thordardottir, M. et al., “Dietary intake is asso­ci­ated with risk of multiple myeloma and its precursor disease,” in PLOS One, November 1, 2018 (full text).