Respiratory disease and lower pulmonary function as risk factors for subsequent dementia: a systematic review with meta-analysis

Russ, Tom C.; Kivimäki, Mika; Batty, G. David

Background In addition to affecting the oxygen supply to the brain, pulmonary function is a marker of multiple insults throughout life (including smoking, illness, and socioeconomic deprivation). By meta-analysing existing studies, we tested the hypothesis that lower pulmonary function and respiratory illness are linked to an elevated risk of dementia. Aims To review the best available evidence, taken from longitudinal studies, for pulmonary function and respiratory disease as risk factors of dementia. Method We conducted a systematic review of longitudinal studies using PubMed until April 1st, 2019 and, where possible, pooled results in random-effects meta-analyses. Results We identified eleven studies relating pulmonary function to later dementia risk, and eleven studies of respiratory illness and dementia (including one which studied both). The lowest quartile of lung function measure Forced Expiratory Volume in one second (FEV1) compared with the highest was associated with a 1.5-fold (1.51, 95%CI 0.94-2.42) increased dementia risk (Ntotal=127,710, 3 studies). Respiratory illness was also associated with increased dementia risk to a similar degree (1.54, 1.30-1.81, Ntotal=288,641, 11 studies). Conclusions Individuals with poor pulmonary function are at increased risk of dementia. The extent to which the association between poor pulmonary function and dementia is causal remains unclear.