Female systemic lupus erythematosus in Miyagi Prefecture, Japan: a case-control study of dietary and reproductive factors.

To investigate risk factors of systemic lupus erythematosus (SLE) in relation to diet and reproduction, a population-based case-control study was conducted during the period from October 1988 to October 1989 in Miyagi Prefecture in northeastern Japan. Included in the study were 52 female patients with the recent SLE onset. Two sex- and birth year-matched (+/- 2 years) controls for each patient were selected from the general population. The analysis on diet showed that the frequent intake of meat was associated with an increased risk (frequent vs. rare, relative risk (RR) 3.36; 95% confidence interval (CI) 1.10-10.24) and that the patients preferred fatty meat such as beef or pork. The analysis on menstrual history revealed that menstrual irregularity was also associated with an increased risk (RR 3.79; 95% CI 1.43-10.01). These results suggest that dietary and reproductive factors may be responsible for the onset and the progression of SLE.