Abstract
Background: Increased lipoprotein (a) (Lp(a)) is associated with coronary risk, but links with stroke have been less consistent. Blacks have 2-4-fold higher Lp(a) levels than whites, and have higher stroke incidence than whites, but have been under-represented in studies of Lp(a) and stroke to date. Hypothesis: Lp(a) is a risk factor for ischemic stroke, and this risk differs by race. Methods: REGARDS recruited 30,239 black and white U.S. men and women in 2003-7 to study regional and racial differences in stroke mortality. We measured Lp(a) by immunonepholometric assay in 572 cases of incident ischemic stroke and a 1,104-person cohort random sample. The hazard ratio of stroke by baseline Lp(a) was calculated using Cox proportional hazards models, stratified by race. Lp(a) was modeled both as a continuous variable (per sex- and race-specific SD) and in sex- and race-specific quartiles, given known differences in distributions by race and sex. Results: As shown in the Figure, being in the 4 th vs 1 st Lp(a) quartile was associated with ischemic stroke in black but not white participants, adjusted for age and sex (Model 1). The HRs were essentially unchanged with added adjustment for stroke risk factors (Model 2). There was no significant association between Lp(a) as a continuous variable and stroke, though race-specific patterns were similar. There remained no association between Lp(a) and stroke in whites when we used the sex- and race-specific 90 th percentile as a cut-off (HR: 0.91 95% CI: 0.52, 1.60). Discussion: Lp(a) was associated with ischemic stroke risk in black but not white REGARDS participants, this might partly explain the black/white disparity in stroke. Further studies in racially diverse groups are necessary to confirm these findings. Figure 1. Hazard ratios for Lp(a) and stroke in blacks and whites, per quartile (compared with first quartile) and SD.
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