A systematic review including 6 case-control studies (a total of 2 375 women with connective tissue disease and over 15 000 controls), 6 cohort studies (a total of 4 040 women with breast implants) and 1 cross-sectional study (150 women with breast implants and 4 079 without) was abstracted in DARE. Individual study risks of breast implants for connective tissue diseases ranged from 0 to 4.5, and all confidence intervals included 1. For 12 studies, the summary relative risk for any connective tissue disease in women with implants compared to women without implants was 0.76 (95% CI 0.55 to 1.04).
Comment: The quality of evidence is upgraded by consistency of results in different types of studies and (nonsignificant) direction of effect (decreased risk with implants).