Association of family stress with natural killer cell activity and the frequency of illnesses in children.

OBJECTIVE To examine prospective associations between chronic stress in the parent-child and family systems and subsequent rates of illnesses and the activity of natural killer (NK) cells in children. DESIGN Prospective cohort study. SETTING The Golisano Children's Hospital at Strong, Rochester, NY, from July 1, 2001, to June 30, 2003. PARTICIPANTS One hundred sixty-nine socioeconomically and racially diverse children (aged 5-10 years) and their parents. Parents completed measures of their psychiatric symptoms and stress in the family every 6 months. Children's blood samples were obtained for NK cytotoxicity assays every 6 months. MAIN OUTCOME MEASURES Parent-reported total child illnesses and febrile illnesses and results of NK cell cytotoxicity assays. We estimated adjusted illness rate ratios and adjusted mean differences in NK activity. RESULTS Elevated parental psychiatric symptoms occurring with family stressors were associated with more total illnesses (rate ratio, 1.11; 95% confidence interval [CI], 1.00-1.22) and febrile illnesses (rate ratio, 1.36; 95% CI, 1.13-1.64) in children. Natural killer cell function was enhanced in children whose parents reported more chronic stress (estimate, 0.15; 95% CI, 0.05-0.26). Natural killer cell function was not associated with short-term changes in stress. Stress-illness relationships were not associated with stress-related alterations in NK cell function. CONCLUSIONS Chronic family stress was associated with increased illnesses in children. Unlike older adults, children living with elevated chronic stress had enhanced rather than decreased NK cytotoxicity, suggesting chronic stress may have different effects on the developing immune system. Impaired parental functioning may be a mechanism linking family stress with adverse effects on children's health.