Uric acid and skin microvascular function: the Maastricht study
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Objective: Microvascular dysfunction has been suggested as a possible underlying mechanism for the association between uric acid and various diseases, such as hypertension, renal disease and cardiomyopathies. We therefore analysed the association between serum uric acid and skin microvascular function, a model of generalized microvascular function. Methods: A cross-sectional study was performed in 610 individuals [51.8% men; mean age 58.7 +/- 8.6 years; 23.6% with type 2 diabetes (by design)] from The Maastricht Study. We assessed skin capillary density (capillaries/mm(2)) by capillaroscopy at baseline, after 4 min of arterial occlusion, and after 2 min of venous congestion. Capillary recruitment after arterial occlusion and during venous congestion was expressed as the absolute change in capillary density after recruitment and as the percentage change in capillary density from baseline. Results: Crude linear regression analyses showed that serum uric acid [per +1 standard deviation (SD) of 74 mu mol/l] was not associated with baseline capillary density [beta = -0.21 (95% confidence interval, 95% CI -1.61 to 1.19) P = 0.765], while an inverse association was found between uric acid and absolute change in capillary density after arterial occlusion [beta = -1.15 (95% CI -2.36 to 0.06) P = 0.062] and during venous congestion [beta = -1.41 (95% CI -2.68 to -0.14) P = 0.029]. However, after adjustment for sex, age and glucose metabolism status, these associations were no longer statistically significant. In addition, we found no association between uric acid and percentage capillary recruitment after arterial occlusion [beta = -1.66 (95% CI -3.97 to 0.65) P = 0.159] or during venous congestion [beta = -2.02 (95% CI -4.46 to 0.42) P = 0.104] in unadjusted analyses; multivariable analyses gave similar results. Conclusion: These results do not support the hypothesis that generalized microvascular dysfunction (as estimated in skin microcirculation) is the underlying mechanism for the association between uric acid and cardiovascular and renal diseases. The possibility that uric acid is associated with microvascular dysfunction in specific end-organs, for example heart or kidney, needs further investigation.