Dietary Pattern and Risk of Monoclonal Gammopathy of Undetermined Significance: A Population-Based Study

Background: All multiple myeloma (MM) cases are preceded by the premalignant state, monoclonal gammopathy of undetermined significance (MGUS). The etiology of MM and MGUS is to a large extent unknown. Few studies on the effect of diet on MM have been conducted and the results have been inconclusive. No studies have been conducted on the effect of diet on MGUS. Studying dietary patterns offers broader view of food consumption and possible effects of diet on diseases since many nutrients and other substances in foods act together. The aim of this study was to identify different dietary patterns at three time points throughout the lifespan and examine whether adherence to these patterns was associated with risk of MGUS and light chain MGUS (LC-MGUS) and progression to MM and other lymphoproliferative diseases.

Methods: This study was based on participants from the AGES-Reykjavik Study (N=5,764; mean age 77 years). Participants gave information on frequency of intake of common foods from early life (14-19 years old), midlife (45-55 years old), and currently at study baseline (67 years and older). All participants were screened for MGUS and LC-MGUS by serum protein electrophoresis and serum free light-chain assay. We identified MM and other lymphoproliferative diseases by cross linking with the Icelandic Cancer Registry. Principal component analysis was used to extract dietary patterns. This method is data driven and forms new linear factors, (dietary patterns) by reducing data dimension and grouping correlated variables (food intake). For each pattern extracted a new variable is created, ranking participants on their adherence to that particular pattern. We used logistic regression to test association between adherence to the early life and midlife dietary patterns and MGUS and LC-MGUS, and Cox proportional hazard regression to test association between adherence to the late life patterns and progression to MM and other lymphoproliferative diseases.

Results: A total of 300 (5.2%) MGUS cases and 52 (0.9%) LC-MGUS cases were identified. During 11 years of follow-up 18 cases had progressed to MM and 10 to other lymphoproliferative diseases. We extracted four dietary patterns from early life, four from midlife, and six from baseline. When analyzing MGUS and LC-MGUS cases combined we found that high adherence to pattern I from early life, the old traditional Icelandic diet (high intake of salted/smoked meat and fish, blood and liver sausage, rye bread, milk, oatmeal, and potatoes), decreased the risk (odds ratio (OR) = 0.89, 95% confidence interval (CI) 0.79-1.00), however no association was found when analyzing MGUS and LC-MGUS separately (Table 1). When analyzing midlife patterns we found that the estimate for pattern I, the old traditional Icelandic diet (high intake of salted/smoked meat and fish, blood and liver sausage, fish in salad or on bread, and meat meals) was similar to the findings from early life, although it did not reach a statistical significance (OR = 0.90, 95% CI 0.80 - 1.02). High adherence to pattern III (high intake of potatoes, whole wheat bread, milk, rye bread, and fish) from midlife decreased the risk of combined MGUS (OR = 0.88, 95% CI 0.79-0.98). When analyzing MGUS and LC-MGUS separately we found that high adherence to pattern III decreased the risk of LC-MGUS (OR = 0.69, 95% CI 0.53-0.90) but not MGUS. We did not find an association between the six patterns from late life and progression to MM. However when analyzing progression to MM and other lymphoproliferative diseases combined we found that high adherence to pattern VI (high intake of meat and milk, low intake of fish) increased the risk of progression (HR = 1.82, 95% CI 1.24-2.67). Further results can be seen in Table 1.

Conclusion: Our findings suggest that high adherence to the old traditional Icelandic diet consumed during early and mid 19^th century, including salted or smoked meat and fish, blood or liver sausage, rye bread, and potatoes decreases the risk of MGUS/LC-MGUS later in life. They additionally suggest an increased risk of progression to MM and other lymphoproliferative diseases, with high adherence to a pattern with high meat and low fish intake. The mechanisms for these findings are unknown but our study suggests that food intake can alter the risk of developing MGUS/LC-MGUS as well as the risk of progression to MM.

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