The red cell distribution width and anemia in association with prevalent dementia

The red cell distribution width (RDW), a measure of anisocytosis, independently predicts cardiovascular disease outcomes and chronic disease mortality. Little is known about the RDW, or the interplay between RDW and anemia, in relation to dementia risk. We evaluated the association between the RDW and prevalent dementia, overall and by anemia status, among 2556 community-dwelling older adults participating in the Chicago Health and Aging Project. RDW measurements came from complete blood counts, and participants underwent diagnosis for dementia according to standard clinical criteria. Five hundred twenty-five participants were diagnosed with dementia. Elevated RDW was associated with increased odds of having dementia: after adjusting for age, sex, race, and education, the odds of prevalent dementia increased progressively over increasing quartile of RDW (Ptrend=0.02), and persons in the highest RDW quartile (≥14.8%) had 42% greater odds of having dementia than those in the lowest quartile [odds ratio (OR), 1.42; 95% confidence interval (CI), 1.05-1.92)]. Per unit (%) increment in RDW, the odds of dementia were higher by 6% (OR, 1.06; 95% CI, 1.00-1.13). Findings were similar upon further adjustment for health behaviors and diabetes. In analyses adjusted for hemoglobin concentration, the RDW-dementia association was attenuated, whereas the inverse association between hemoglobin and dementia remained significant. However, RDW was associated with dementia more strongly among participants without anemia (OR, 1.09; 95% CI, 1.00-1.43) than among those with anemia (OR, 0.99; 95% CI, 0.86-1.18), although this difference was not statistically significant. The RDW, a readily available and inexpensive hematologic measure, may offer novel information about dementia risk, particularly among persons without anemia. Future studies should establish the RDW's ability to predict risk prospectively.