Hemoglobin Concentration and the Incidence of Stroke in the General Japanese Population: The Jichi Medical School Cohort Study

BACKGROUND Several studies have described an association between hemoglobin concentration and stroke; however, the influence of hemoglobin on stroke incidence has not been fully revealed. Our objective was to elucidate the association between hemoglobin concentration and stroke incidence in Japanese community residents. METHODS In the present study, we collected the data of 12,490 subjects who were enrolled between April 1992 and July 1995 in the Jichi Medical School (JMS) Cohort Study. We excluded the subjects with a history of stroke. Hemoglobin concentrations were grouped in quartiles, and quartile 2 (Q2) was used as the reference category. A Cox proportional-hazards model was used to examine hazard ratios (HRs) and the stroke incidence rates with 95% confidence intervals (CIs). RESULTS During 10.8 years of follow-up, 409 participants (212 men and 197 women) experienced a new stroke, including 97 intracerebral hemorrhages, 259 cerebral infarctions, and 52 subarachnoid hemorrhages (SAH). In sex-specific hemoglobin quartiles, the multivariate-adjusted HR was statistically significantly higher in Q1 than in Q2, and a relationship similar to a J shape was observed between all strokes (HR in Q2 vs. Q1, 1.36; 95% CI, 1.02-1.83; Q3, 1.20; 95% CI, 0.87-1.64; and Q4, 1.16; 95% CI, 0.84-1.60). Furthermore, the analysis of stroke subtypes showed a statistically significantly higher multivariate-adjusted HR in Q1 than in Q2 for SAH (HR, 2.61; 95% CI, 1.08-6.27). CONCLUSIONS A low hemoglobin concentration was associated with an increased risk of stroke, which was strongly influenced by the incidence of SAH.