Sex differences in the impact of diabetes on mortality in chronic dialysis patients

Background. Although females have a survival advantage in the general population, women undergoing dialysis have similar mortality to men. Because the reasons for this difference are unknown, we hypothesized that sex differences in cardiovascular disease (CVD) risk profile exist at dialysis initiation and that the association of such risk factors with mortality differs between sexes. Methods. This study was a prospective observational cohort study (NECOSAD) of incident dialysis patients with 5 years of follow-up where we calculated male: female odds ratios (OR) and relative risks of mortality (hazard ratio, HR) for the presence of CVD risk factors at the start of dialysis. We also examined the presence of interaction between sex and CVD risk factors in their association with mortality. Results. In 1577 patients (61% men, 60 +/- 15 years), men presented more CVD co-morbidity [OR: 1.88 (95% CI: 1.51, 2.35)] but less diabetes mellitus (OR: 0.70 [0.55, 0.89]) than women. Both sexes presented equal survival [HR 0.98 (0.83, 1.16)]. Women with diabetes had a higher mortality risk [HR 2.93 (2.27, 3.79)] than their male counterparts [HR 1.99 (1.52, 2.59)], showing an interaction effect between sex and diabetes [relative excess risk due to interaction 1.18 (0.37, 2.00)]. Conclusion. Despite a lower prevalence of CVD, women starting dialysis had the same mortality risk as men. The mortality risk was strikingly higher in diabetic women than diabetic men. This excess mortality may help explain why dialysis cancels out the female survival advantage. Our study identifies a high-risk group of patients that may warrant further investigation and intensified therapeutic care.