Does inflammation explain the link between multiple sensory impairment and dementia?

Background Multiple sensory impairments are associated with increased risk of dementia, but the underlying mechanisms are unclear. One potential explanation is that the association is due to shared risk factors such as inflammation. Our objective was to evaluate whether multisensory impairment was associated with markers of inflammation (interleukin‐6, and C‐Reactive Protein (CRP) independent of other health conditions and test whether inflammation might explain the association between multisensory impairments and dementia risk. Method We studied 1,794 black and white older adults from the Health, Aging, and Body Composition Study, a prospective cohort study of older adults who were aged 70‐79 and dementia‐free at enrollment. Sensory abilities were assessed at study years 3‐5, vision was measured by log contrast sensitivity, hearing by pure tone average at 500, 1,000, 2,000, and 4,000 Hz; smell by the 12‐item Cross Cultural Smell Identification Test; and touch by vibration detection threshold of the big toe. A multisensory score (0‐12) was calculated based on sample quartiles and summed across each sensory domain. Interleukin‐6, and CRP were assayed based on blood sample near baseline and log transformed. Incident dementia over follow‐up was determined based on a combination of hospitalization records, dementia medications, or clinically significant cognitive decline. Using regression models, we investigated the associations between inflammation biomarkers, multisensory impairment, and dementia with adjustment for demographics, health conditions, and health behaviors. Result Both measures of inflammation were associated with higher multisensory impairment scores. 1‐log interleukin‐6 was associated with 0.25 points worse multisensory score (95%CI: 0.10, 0.40; p>0.001), 1‐log CRP levels was associated with 0.11 points worse multisensory score (95%CI: 0.01, 0.20; p=0.02). Higher level of interleukin‐6 (HR = 1.18; 95% CI: 1.02, 1.37; p=0.03) but not CRP (p=0.84) was associated increased dementia risk. In adjusted models, a 1‐point increase in the multisensory score was associated with a 14% higher risk of dementia (95% CI: 1.08; 1.20), estimates were similar even after including interleukin‐6 as an explanatory variable. Conclusion Inflammation was independently associated with worse multisensory impairment scores. Although inflammation is also associated with dementia, it did not explain the association between multisensory impairment and dementia.