The relationship between anaemia, haemoglobin levels, and cognitive function: Evidence in two population-based cohorts from India and the United States.
Winchester LM., Newby D., Ghose U., Hu P., Green H., Chien S., Ranson JM., Faul J., Llewellyn D., Lee J., Bauermeister S., Nevado-Holgado A.
BACKGROUND: In India, studies of anaemia in older populations are lacking despite the adverse effect on cognitive function and dementia. The Longitudinal Ageing Study in India-Harmonized Diagnostic Assessment of Dementia (LASI-DAD) dataset contains detailed measures to allow better understanding of anaemia as a potential risk factor for dementia. METHOD: Linear regression was applied in the LASI-DAD cohort (n = 2758) between blood measures (including anaemia and haemoglobin concentration (g/dL)) with 11 cognitive tests. All models were adjusted for age and gender (full model includes rural location, education, smoking, region, BMI and population weights). The USA-based Health and Retirement Study (HRS) cohort (n = 5720) was used to replicate associations between blood and global cognition. RESULTS: In LASI-DAD, we showed an association between anaemia and poor memory (p-value = 0.0054). We found a positive association between haemoglobin concentration and ten cognitive tests (β = 0.041-0.071,p-value<0.05). The strongest association with haemoglobin was identified for memory-based tests (β = 0.061-0.071,p-value<0.005). Positive associations were shown between the general cognitive score and red blood count tests including mean corpuscular haemoglobin concentration (MCHC,β = 0.06,p-value = 0.0001) and red cell distribution width (RDW,β = -0.11,p-value<0.0001). In the HRS, associations were replicated between general cognitive score and other blood count tests (Red Blood Cell, MCHC, RDW, p-value<0.05). CONCLUSIONS: We have established in a South Asian population that low haemoglobin and anaemia are associated with low cognitive function, therefore indicating that anaemia could be an important modifiable risk factor for dementia. We have validated this result demonstrating both the variability of this risk factor cross-nationally and its generalizable association with cognitive outcomes.