Poor sleep is associated with higher plasma proinflammatory cytokine interleukin-6 and procoagulant marker fibrin D-dimer in older caregivers of people with Alzheimer's disease

OBJECTIVES: To determine whether objective measures of sleep correlate with plasma levels of the proinflammatory cytokine interleukin (IL)-6 and the procoagulant marker fibrin D-dimer in caregivers of patients with dementia. DESIGN: Cross-sectional study. SETTING: Subjects' homes. PARTICIPANTS: Sixty-four community-dwelling spousal caregivers (69% women, mean age +/- standard deviation 72 +/- 9) and 36 sex-matched noncaregiving controls. MEASUREMENTS: All participants underwent in-home full-night polysomnography. Demographic and lifestyle factors, depression, diseases, and medication that could affect inflammation, coagulation, and sleep were controlled for in analyses regressing sleep variables and caregiver status and their interaction on plasma levels of IL-6 and D-dimer. RESULTS: Caregivers had higher levels of D-dimer (781 +/- 591 vs 463 +/- 214 ng/mL, P=.001) and IL-6 (1.42 +/- 1.52 vs 0.99 +/- 0.86 pg/mL, P <.06) and lower levels of total sleep time (369 +/- 70 vs 393 +/- 51 minutes, P=.049) and sleep efficiency (77 +/- 11 vs 82 +/- 9%, P=.04) than controls. After controlling for age and body mass index, longer wake time after sleep onset (change in coefficient of determination (Delta R-2)=0.039, P=.04) and the interaction between caregiver status and higher apnea-hypopnea index (Delta R-2=0.054, P=.01) were predictors of IL-6. Controlling for age, caregiver status independently predicted D-dimer levels (Delta R-2=0.047, P=.01). Controlling for age and caregiver status, lower sleep efficiency (Delta R-2=0.032, P=.03) and the interaction between caregiver status and more Stage 2 sleep (Delta R-2=0.037, P=.02) independently predicted plasma D-dimer levels. CONCLUSION: Poor sleep was associated with higher plasma IL-6 and D-dimer levels. These effects were most pronounced in caregivers of subjects with Alzheimer's disease. The findings suggest a mechanism that may explain how disturbed sleep might be associated downstream with cardiovascular risk, particularly in older people under chronic stress.