Objective: To investigate the associations among depression, smoking behaviour and enumerative measures of immunity in a population-based cohort study.
Methods: Participants in the European Prospective Investigation into Cancer and Nutrition in Norfolk, England, aged 40-80 years, were identified through age-sex general practice registers. After exclusions for prevalent conditions, white blood cell (WBC) counts and a measure of depressive episode history were available from 11,367 participants and, after a mean interval of 44 months, from 11,857 at a second health check. The measure of depression was completed between health checks.
Results: Observed associations between leukocyte counts and depression for men were weakened following adjustment for cigarette smoking. There was an incremental elevation in age-smoking adjusted mean WBC count by recency of depression such that there was a 3.1% (P=.03) and 5.6% (P=.0004) difference across depression history subgroups (never, lifetime, current) at the first and second health checks, respectively. No age-smoking adjusted associations were observed for women.
Conclusion: Following adjustment for age and cigarette smoking, these data provide evidence for an association between major depressive disorder and leukocyte counts for men, but not for women.