Plasma Beta Amyloid Level and Depression in Older Adults

Background. Older adults with depression have an increased risk of developing dementia. Low plasma beta-amyloid 42 (A beta 42) and A beta 42/A beta 40 have emerged as promising biomarkers of dementia. The association between depression and plasma A beta is unclear. Methods. In this longitudinal study of 988 community-dwelling elders from the Health Aging and Body Composition study, depression was assessed with the Center for Epidemiologic Studies-Depression Scale 10-item version. We determined the association between A beta 42 and A beta 42/A beta 40 tertile and depression at baseline and over 9 years. We also stratified the models to determine if apolipoprotein E e4 allele status modified the associations. Results. Mean baseline age was 74.0 +/- 3.0 years, 51(5.2%) participants had depression, 545 (55.2%) were women, 531 (53.7%) were black, and 286(30.7%) had one or more apolipoprotein E e4 allele. At baseline, there was no association between A beta 42/A beta 40 or A beta 42 and depression. Over 9 years, 220 (23.5%) participants developed depression. In adjusted Cox proportional hazards models, among those with one or more e4 allele, low A beta 42/A beta 40 was associated with an increased risk of developing depression over time (low 10.8% vs high 3.2%, hazard ratio = 2.38, 95% confidence interval: 1.15-4.92). Among those with no e4 allele, there was no association between A beta 42/A beta 40 and risk of depression over time (13.3% vs 17.5%, hazard ratio = 0.80, 95% confidence interval: 0.52-1.23; p value for interaction = .003). Conclusions. The association between low plasma A beta 42/A beta 40 and increased risk of incident depression among those with one or more apolipoprotein E e4 allele implies a synergistic relationship similar to that found with dementia. Future work should investigate the interrelationships among plasma A beta 42/A beta 40, depression, and dementia.