and report baseline characteristics of the 10,975 ARIC women and men included in the study according to quartiles of FEV1 at visit 2. Individuals with worse lung function were more likely to be older, African-American, smokers, less educated, diabetic, hypertensive, and more likely to have higher body mass index and the APOEε4 allele. A similar pattern was observed for FVC (data not shown).
Selected characteristics of study participants by quartiles of forced expiratory volume in 1 second (FEV1), women, ARIC Study, 1990–1992. Numbers correspond to means (standard deviation) or percentages.
Selected characteristics of study participants by quartiles of forced expiratory volume in 1 second (FEV1), men, ARIC Study, 1990–1992. Numbers correspond to means (standard deviation) or percentages.
In cross-sectional analysis, individuals with lower FEV1 and FVC at visit 2 scored lower in the cognitive tests, even after adjustment for multiple confounders (). In multivariable analysis, DWR, DSS and WF among those in the lowest quartile of FEV1 were 0.15 (95% 0.07, 0.24), 1.6 (95% 1.1, 2.2) and 1.2 (95% CI 0.5, 1.8) points lower, respectively, than among those in the upper quartile. Results were similar for FVC or for the sample restricted to nonsmokers (), after additionally adjusting for height or vital exhaustion, or using percent of predicted lung function as the main exposure (data not shown). No clear associations with cognitive tests were found for the FEV1/FVC ratio. Compared to individuals with a normal ventilatory pattern, those with restrictive or mixed patterns had lower scores in cognitive tests, while no association was found between obstructive ventilatory pattern and cognitive tests ().
Difference in cognitive score by gender-specific quartiles of FEV1, FVC and FEV1/FVC at visit 2, ARIC Study, 1990–1992.
Difference in cognitive score by patterns of ventilatory function at visit 2, ARIC Study, 1990–1992
The average decline in cognitive test scores between ARIC visit 2 and 4 was 0.14 (95% CI 0.11–0.17) for DWR, 2.5 (95% CI 2.4–2.7) for DSS, and 0.47 (95% CI 0.31–0.64) for WF. Neither FEV1 nor FVC at ARIC visit 2 were associated with change in cognitive score between both visits (supplement table S1
). Among 904 ARIC participants who had two additional cognitive assessments (the last one in 2004–2006), the average decline per 10 years (and 95% CIs) was 0.53 (0.45, 0.61) for DWR, 3.1 (2.8, 3.4) for DSS, and 1.3 (1.0, 1.6) for WF. Overall, individuals included in this analysis had slightly better pulmonary function and cognitive scores than the entire cohort. For example, age, gender and race-adjusted mean FVC was 3.7 L vs. 3.6 L in those included and not included (p<0.001), and mean DWR was 6.7 vs. 6.4 in each group (p<0.001). As in the analysis considering only two cognitive assessments, pulmonary function tests were not associated with changes in cognitive score over time (supplement table S2
We also studied the association of lung function with incidence of dementia hospitalization among 9837 ARIC participants. During a median follow-up of 14.1 years, 205 cases of dementia hospitalization were identified. Both FEV1 and FVC were associated with this outcome. The HR (95% CI) of dementia hospitalization among those in the lowest quartile of FEV1 compared to those in the highest one was 1.6 (0.9, 2.3). The corresponding figure for FVC was 2.1 (1.2, 3.7) (). The FEV1/FVC ratio was not associated with the incidence of dementia hospitalization. Consistently, dementia risk was higher among individuals presenting a restrictive ventilatory pattern (HR 1.6, 95% CI 1.0–2.6, in an age, gender, and race-adjusted analysis, and 1.4, 95% CI 0.9–2.3 in a multivariable model), but not among those with obstructive or mixed ventilatory patterns (multivariable HR 1.0, 95% CI 0.7–1.4 and 1.3, 95% CI 0.7–2.3, respectively), compared to normal.
Hazard ratios (95% confidence intervals) of dementia hospitalization by quartiles of FEV1, FVC and FEV1/FVC ratio at visit 2, ARIC, 1990–2005
Associations were similar in individuals with or without the APOE
ε4 allele. However, gender and race modified the association of lung function with cognitive scores in the cross-sectional analysis. Worse lung function was more strongly associated with lower scores in the cognitive tests in women and African-Americans, compared to men and whites, respectively ( and supplement table S3
). However, no differences by gender, race, or APOE genotype were found for the associations of lung function with dementia hospitalization or cognitive score change (data not shown). Finally, age did not modify the association of lung function with cognitive function in cross-sectional or longitudinal analysis, but in younger individuals (≤60 at baseline) worse lung function was more strongly related with the incidence of dementia hospitalization than in the older group (). HR (95% CI) of dementia comparing extreme quartiles of FEV1 was 1.7 (0.8, 4.0) in those 60 or younger, and 1.3(0.6, 2.8) in older participants (p for interaction=0.07), while the corresponding figures for FVC were 2.5 (1.0–6.6) for younger and 1.6 (0.8–3.2) for older participants (p for interaction=0.02)
Cognitive score difference by 1 liter increase in FEV1 or FVC at visit 2, ARIC, 1990–1992. Analysis stratified by gender, race, and APOE genotype.
Figure 2 Cumulative risk of dementia hospitalization by FEV1 and FVC and by age (≤60 or >60). Low and high FVC or FEV1 defined as extreme quartiles (low: quartile 1, high: quartile 4). Results are based on survival curves from a Cox model, adjusting (more ...)