Homocysteine or Renal Impairment: Which is the real cardiovascular risk factor?

Objective-The purpose of this study was to determine whether adjustment for renal function eliminates the relationship between total plasma homocysteine (tHcy) and vascular risk, assessed by carotid intima medial thickness (CIMT) and flow-mediated dilation (FMD) of the brachial artery.Methods and Results-We used cross-sectional data from 173 stroke patients treated with B-vitamins (folic acid 2 mg, vitamin B-6 25 mg, and vitamin B-12 0.5 mg) or placebo in a randomized double-blinded trial to test the relationships between posttreatment tHcy, cystatin C (a marker of glomerular filtration rate), estimated glomerular filtration rate (eGFR, Modification of Diet in Renal Disease equation) creatinine, CIMT, and FMD in stepwise and multivariable regression models. The strong linear relationship between tHcy and cystatin C was not altered by long-term B-vitamin treatment. tHcy lost significance as a predictor of the vascular measurements after adjustment for any single marker of renal function. Cystatin C, but not tHcy, was a significant independent predictor of FMD after adjustment for age, sex, smoking, systolic blood pressure, high-density lipoprotein cholesterol, and treatment group.Conclusions-Adjusting for renal function eliminates the relationship between tHcy and CIMT and FMD, supporting the hypothesis that elevated tHcy is a marker for renal impairment rather than an independent cardiovascular risk factor.