In older adults, both low (anemia) and high (polycythemia) hemoglobin (Hb) have been associated with health problems, including cardiovascular and thromboembolic events and cognitive decline. A recent prospective cohort study in the U.K. evaluated the association between Hb and long-term mortality by age and sex. Baseline Hb was measured at 22 assessment centers at enrollment in 502,188 individuals (medium age at enrollment, 58 years; age range, 37-73 years; 46% men) from 2006 to 2010; individuals were followed for a median of 13.6 years. Almost two-thirds (65%) of participants had an enrollment Hb 1 to 3 g/dL above the World Health Organization (WHO) definition of anemia (< 13.0 g/dL for men and <12.0 g/dL for women), while only 4.4% met the WHO criteria for anemia and 1.0% had high hemoglobin levels or polycythemia (>4.0 g/dL over the WHO thresholds for anemia). Hemoglobin levels varied based on sex and age—women were more likely than men to have lower Hb levels but this difference narrowed with age. Mortality based on any cause, a cardiovascular event or cancer all followed a U-shaped curve across Hb levels with the highest rates of mortality in those >2 g/dL below the WHO threshold for anemia or >4 g/dL above the threshold. While study participants were predominantly white and healthy, further research is needed in other populations and to determine if treating the causes of anemia and polycythemia improves long-term outcomes.
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