Interaction of greenness and polygenic risk score of Alzheimer's disease on risk of cognitive impairment

Studies have shown contact with nature has positive psychological, neurological, and cognitive benefits. Whether the built environment can affect genetic predisposition of Alzheimer's disease (AD) should be explored. We aimed to examine whether greenness around the residential environment can modify the effect of genetic AD risk on cognitive function. We used a genetic sub-study of the Chinese Longitudinal Healthy Longevity Survey including 1199 older adults (mean age: 100.3 ± 3.4 years) aged 90 years old or older. We used Polygenic Risk Score (PRS) to quantify the genetic AD risk and two types of measurements based on Normalized Difference Vegetation Index (NDVI) to access the residential greenness (contemporaneous and annual average NDVI). Contemporaneous NDVI values were the NDVI value collected at the corresponding survey, and the annual average NDVI was the average value of NDVI during the year before the corresponding survey. We defined cognitive impairment as having a Mini-Mental State Examination score below 25. In the multivariable logistics regression models, contemporaneous NDVI and genetic AD risk were associated with cognitive impairment. Among those with low genetic AD risk, the risk of cognitive impairment was lower in those living around higher greenness (contemporaneous NDVI OR: 0.55, 95% CI: [0.34, 0.86]; Pinteraction: 0.071; annual average NDVI OR: 0.49, 95% CI: [0.31, 0.79]; Pinteraction: 0.040). We did not observe significant associations between greenness and cognitive impairment among those with high genetic AD risk. Prevention efforts using PRS warrant a higher granularity of environmental exposures and biological etiology data.