Abstract and Introduction
Background: Depressive disorders are highly prevalent, have a detrimental impact on the quality of life of patients and their relatives and are associated with increased mortality rates, high levels of service use and substantial economic costs. Current treatments are estimated to only reduce about one-third of the disease burden of depressive disorders. Prevention may be an alternative strategy to further reduce the disease burden of depression.
Methods: We conducted a meta-analysis of randomized controlled trials examining the effects of preventive interventions in participants with no diagnosed depression at baseline on the incidence of diagnosed depressive disorders at follow-up. We identified 32 studies that met our inclusion criteria.
Results: We found that the relative risk of developing a depressive disorder was incidence rate ratio = 0.79 (95% confidence interval: 0.69–0.91), indicating a 21% decrease in incidence in prevention groups in comparison with control groups. Heterogeneity was low (I 2 = 24%). The number needed to treat (NNT) to prevent one new case of depressive disorder was 20. Sensitivity analyses revealed no differences between type of prevention (e.g. selective, indicated or universal) nor between type of intervention (e.g. cognitive behavioural therapy, interpersonal psychotherapy or other). However, data on NNT did show differences.
Conclusions: Prevention of depression seems feasible and may, in addition to treatment, be an effective way to delay or prevent the onset of depressive disorders. Preventing or delaying these disorders may contribute to the further reduction of the disease burden and the economic costs associated with depressive disorders.
About 150 million people worldwide are affected with depression at any moment in time, and one in every five women and 1 in every eight men experience an episode of major depression over the course of their life.[1–3]
Depression is a major factor in quality of life decrements and is also associated with premature death. People suffering from depressive disorders experience substantial loss in quality of life. Between 1990 and 2010, major depression moved up from 15th to 11th in terms of global disease burden measured in disability-adjusted life years (DALYs) and it is projected to become the single leading cause of disease burden by 2030. Depressive disorders are associated with high levels of service use and economic costs stemming from productivity losses. Although effective treatments are available, it has been estimated that, even under optimal conditions, contemporary treatments can reduce only about one-third of the disease burden associated with major depressive disorder (MDD).[9,10]
A way to further reduce the disease burden of major depression could be to reduce the influx of new cases that is, to reduce the incidence. This is done by prevention rather than treatment. Strengthening protective factors (e.g. social, cognitive or problem-solving skills) or alleviating prodromal disease stages (e.g. reducing severity of depressive symptoms) have been investigated in a considerable number of preventive studies.[11–13] Several studies examining the effects of preventive interventions have found favourable effects on the incidence of new cases,[14–20] but several others did not.[21–24] Whether the effect of the currently available preventive interventions decays over time, indicating effectiveness only when a person is participating in the preventive intervention, is being investigated.
There are different types of prevention. Universal prevention focuses on the general public or a whole population group regardless of risk status. Selective prevention targets individuals or subgroups that are at higher risk of developing mental disorders than average individuals or subgroups. Indicated prevention focuses on individuals who are identified as having prodromal symptoms or biological markers to mental disorders, but who do not yet meet the diagnostic criteria for a full-blown diagnosis.[25,26] In a previous meta-analysis of studies examining the effects of preventive interventions on the incidence of new cases, we found an overall effect of universal, selective and indicated prevention on the incidence of depressive disorders. Universal prevention was only examined in two studies and it was therefore impossible to investigate effectiveness.[21,27] The studies included in that meta-analysis were conducted among various populations and the interventions differed considerably, which might have influenced the results.
One way to examine whether preventive interventions are effective is to look at the numbers needed to treat (NNT). The NNT indicates the number of people who would have to receive a preventive intervention in order to prevent one new case of depression. This leads to the expectation that NNT is inversely related to the a priori risk of the disorder (i.e. lower NNTs in indicated prevention).
In our earlier meta-analysis we could include 19 trials examining the effects of preventive interventions, whereas we identified 32 studies for the current meta-analysis, using even more stringent criteria for inclusion. It was therefore deemed opportune to update the earlier meta-analysis, thus allowing us to not only estimate the overall effects of preventive interventions with greater precision, but also to examine characteristics of the interventions and participants as moderators of outcome. In addition, the large number of included studies allows us to examine subfields of prevention in more detail and with greater statistical power, such as prevention of postpartum depression, prevention at schools and prevention of depression in people with somatic illnesses. Also, we focus on whether the effect of type of intervention decays over time, thereby investigating if type of intervention works as a protection or inoculation against new onsets of MDD.
Int J Epidemiol. 2014;43(2):318-329. © 2014 Oxford University Press
Copyright 2007 International Epidemiological Association. Published by Oxford University Press. All rights reserved.