Lay Summary

This study compared the risk of MCI in UK military veterans and the general population with or without depression. We found the risk of MCI was higher in military veterans with depression compared to the general population without depression but not those in the general population with depression. These findings are important as it suggests depression maybe a potential clinical marker for identifying individuals with MCI who may progress to develop dementia.

Background

Depression is prevalent in military veterans, and this is of particular concern as depression is a risk factor of Mild Cognitive Impairment (MCI) in the general population. Due to limited findings of this associated risk in UK military veterans, the objectives were to investigate if depression is a risk factor of MCI in ageing UK military veterans compared to the general population.

Methods

We performed a prospective cohort study using data from the PROTECT study of participants (n=13,440) who were followed-up over 6 years between 2014-2022. Military veteran status was defined as a history of serving (and no longer serving) in the UK Armed Forces. Depression caseness was identified using the PHQ-9. MCI was defined as objective cognitive impairment (≥1 SD below the mean in either the Digit span, Paired Associated Learning, Verbal reasoning, the Self-ordered search test, Stroop test or the Trails Making test part B) and subjective cognitive impairment (using the IQCODE). Multivariate Cox proportional models were used to examine time to MCI in military veterans and non-veterans with or without depression.

Results

At baseline, military veterans were older than non-veterans (mean age: 65±8.9 vs 61±7.1 years). The proportion of depression caseness did not significantly differ between military veterans and non-veterans (19.8% vs 20.2%, p>0.05). Military veterans with depression were at a significant increased risk of MCI (HR=1.49, 95% CI 1.30-1.72) compared to non-veterans without depression. Although, the risk of MCI in military veterans with depression did not significantly differ to non-veterans with depression (HR=1.41, 95% CI 1.41-1.53).

Conclusion

In this population-based cohort study, the finding’s showed depression is an important risk factor of MCI in UK military veterans and non-veterans.