Purpose: Mental health problems are associated with sickness absence (SA). The present study aimed at establishing which symptoms-distress, depression, anxiety, or somatization-at which symptom levels were associated with SA frequency and duration. Moreover, a number of possible confounders or effect modifiers were taken into account.
Methods: A survey was completed by 3,678 employees of a large Dutch telecom company. Symptoms were measured using the Four-Dimensional Symptom Questionnaire (4DSQ). SA data were registered by the company's occupational health service during the 12 months' period following the survey. Poisson regression was used to analyze the number of SA spells (SA frequency). Negative binomial regression was used to analyze the total number of SA days (SA duration).
Results: In the bivariate analyses distress, depression, anxiety, and somatization impacted on SA frequency and duration. In the multivariate analyses, anxiety and depression turned out not to be directly associated with SA, suggesting that the effect of anxiety and depression was due to the association between anxiety/depression and distress/somatization. Regarding the SA frequency, the rate ratio for 'subclinical' distress was 1.13 (95% CI 1.03-1.25), for 'clinical' distress 1.26 (1.08-1.47), for 'subclinical' somatization 1.34 (1.23-1.46), and for 'clinical' somatization 1.69 (1.46-1.95). Regarding the SA duration, the count ratio for 'subclinical' distress was 1.15 (95% CI 0.91-1.44), for 'clinical' distress 1.50 (1.04-2.16), for 'subclinical' somatization 1.34 (1.10-1.64), and for 'clinical' somatization 1.45 (1.04-2.03).
Conclusions: Somatization and distress are key to understand why depression and anxiety are related to SA.