Risk factors for IgA nephropathy: A case-control study with incident cases in Japan

Background/Aim: Our previous study with prevalent cases suggested that some genetic, immunological and lifestyle-related factors increased the risk of immunoglobulin A nephropathy (IgAN). To confirm this hypothesis, we conducted another case-control study. Methods: The study included 116 incident cases and 276 sex-, age-and residence-matched controls in central Japan. Information on family and individual history and on lifestyle was collected using a self-administered questionnaire. The strength of association between IgAN and a potential risk factor was assessed by calculating an odds ratio. Results: A family history of chronic glomerulonephritis, susceptibility to the common cold, episodes of tonsillitis in the preceding year, preference for salty foods and a high intake of rice and n-6 polyunsaturated fatty acids (PUFA) were associated with an increased risk of IgAN. Coffee consumption and dietary calcium intake were somewhat negatively related to the risk. A significance of alcohol drinking, use of vitamin supplements, consumption of raw eggs and intake of nutrients other than n-6 PUFA and calcium, though previously suggested, was not shown in the present study. Conclusion: Our findings imply that some genetic factors, immune response to infections in the upper respiratory tract and nutritional imbalance would promote the development of IgAN.