Objective. The etiology of mixed connective tissue disease (MCTD) has not been elucidated in detail. Case control studies of MCTD and systemic lupus erythematosus (SLE) were conducted in order to compare factors related to these two diseases. Methods. We selected 48 MCTD and 54 SLE female patients throughout Japan from 2009 to 2010. Controls were 182 female patients who visited the clinics of general internal medicine during the study periods. Results. Smoking and walking a longer time showed an increased age-adjusted risk for MCTD as well as SLE. On the other hand, frequent intake of bread increased the risk of MCTD and high intake of green tea decreased the risk of MCTD. Even after an additional adjustment of smoking and drinking, frequent intake of bread increased the risk of MCTD, while walking increased the risk of SLE. Conclusion. The present study suggests that Westernization of dietary habits (i.e. frequent intake of bread and low intake of green tea) may increase the risk of MCTD, while walking may increase the risk of SLE (probably due to exposure to the sunlight) among Japanese females. Further studies are needed to confirm the result of the present study.
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