Depression, chronic diseases, and decrements in health: results from the World Health Surveys.

BACKGROUND: Depression is an important public-health problem, and one of the leading causes of disease burden worldwide. Depression is often comorbid with other chronic diseases and can worsen their associated health outcomes. Few studies have explored the effect of depression, alone or as a comorbidity, on overall health status. METHODS: The WHO World Health Survey (WHS) studied adults aged 18 years and older to obtain data for health, health-related outcomes, and their determinants. Prevalence of depression in respondents based on ICD-10 criteria was estimated. Prevalence values for four chronic physical diseases--angina, arthritis, asthma, and diabetes--were also estimated using algorithms derived via a Diagnostic Item Probability Study. Mean health scores were constructed using factor analysis and compared across different disease states and demographic variables. The relation of these disease states to mean health scores was determined through regression modelling. FINDINGS: Observations were available for 245 404 participants from 60 countries in all regions of the world. Overall, 1-year prevalence for ICD-10 depressive episode alone was 3.2% (95% CI 3.0-3.5); for angina 4.5% (4.3-4.8); for arthritis 4.1% (3.8-4.3); for asthma 3.3% (2.9-3.6); and for diabetes 2.0% (1.8-2.2). An average of between 9.3% and 23.0% of participants with one or more chronic physical disease had comorbid depression. This result was significantly higher than the likelihood of having depression in the absence of a chronic physical disease (p