Study: General service in the US military may lower the risk of depression

General service in the US military may lower, rather than heighten, the risk of depression, despite the relatively high prevalence of the condition among active duty and veteran personnel, finds a large observational study published online in BMJ Military Health.

The potentially protective effects of military service challenge some previous assumptions about its overall effects on mental health, suggest the researchers.

The military environment can foster the development and progression of depression, as a result of the enforced separation from loved ones and support systems and the emotional and physical toll taken by experiences of combat, point out the researchers. But it can also shape personal growth and enhance coping skills, they add. 

To explore this further, the researchers looked at the potential associations between military service and the risk of depression, drawing on data from five cycles of the nationally representative US National Health and Nutrition Examination Survey (NHANES) from 2011 to 2023. 

Depression was assessed using the Patient Health Questionnaire (PHQ-9), which scores the frequency of 9 depressive symptoms experienced in the past 2 weeks from 0 to 3, where 3 represents 'nearly every day'. 

A total score for all 9 symptoms of 0–4 indicates no depression; 5–9 mild depression; 10–14 moderate depression; and 15 or higher severe depression. A score of at least 10 is considered indicative of clinically significant depressive symptoms.

Among the 25,949 respondents, 2407 had served in the military which, when weighted, corresponds to 8,847,416 people; 23,542 hadn't, corresponding to 89,206,647 people. 

In all, 2548 respondents were identified as having depression, weighted to represent 8,852,943 people, while 23,401 didn't, corresponding to 89,201,120 people. 

The overall prevalence of depression was nearly 9.5%, and 7.5% among those who had served in the military. 

Significant differences were observed, depending on military service and a diagnosis of depression. These included age, sex, race, marital status, education level, income, and the presence of high blood pressure, high cholesterol, and diabetes.

After accounting for potentially influential factors, including non-Hispanic Black ethnicity, marriage, and a high income, military service was associated with a 22% lower risk of depression compared with no time spent in the Armed Forces. 

And after further adjustments for high blood pressure, high cholesterol, and diabetes, military service was associated with a 23% lower risk of depression.

Among the 2407 veterans, 213 were diagnosed with depression. The unadjusted prevalence of depression among veterans didn't differ significantly from that of anyone else. 

But after accounting for potentially influential factors, female sex and being unmarried or divorced emerged as significant risk factors for depression, while a high income and the absence of high blood pressure were seemingly protective. Active service didn't emerge as a significant risk factor.

This is an observational study, and no firm conclusions can be drawn about cause and effect. The researchers acknowledge that they lacked information on veterans' experiences of combat, and that type and length of service, experience of trauma, and serious illness can all influence depression risk.

But they suggest: "While the prevalence of depression is notably high among both active duty personnel and veterans, this large-sample cross sectional study does not support the conclusion that military service increases the risk of depression."

They explain: "Previous research has indicated that the incidence of depressive symptoms among veterans is nearly double that of the general population; however, these studies often involve samples drawn from healthcare systems, which may not accurately represent the broader community."

They conclude: "The NHANES database used in this study provides a representative sample of the US population, confirming that military service may, in fact, serve as a protective factor against depression after adjusting for sociodemographic variables."