Background The possible causal association between depression and cardiovascular disease might be partly explained by an increased risk of hypertension. Several epidemiological studies have investigated the role of depression in the development of hypertension but the evidence is inconclusive. A previous systematic review of these studies has a number of shortcomings, including inappropriate pooling of different effect measures and lack of inclusion of all relevant studies. Additional primary studies have also been published since this earlier review was completed. Our aim was to identify, critically appraise, and synthesise evidence on the association between depression and subsequent hypertension.

Methods We performed a systematic electronic search in PsycINFO, Medline, and EMBASE to identify cohort or longitudinal studies reporting on the risk of hypertension among participants with versus without depressive symptoms and/or clinical depression. We restricted our search to articles published in English. We extracted information on study characteristics, methodology, and results using customised data extraction forms and assessed study quality using the SIGN checklist for cohort studies. We used Stata 14 to perform random effects meta-analyses, to obtain summary effect estimates for the effect of depression on hypertension, pooling hazard ratios and odds ratios separately. We also separately combined studies which defined depression as a categorical or a continuous variable.

Results After de-duplication, the search identified 7402 studies. Twenty-two studies were eligible for inclusion in the review, 17 of which were included in the meta-analyses. Meta-analyses showed an increased hypertension risk among depressed versus non-depressed participants (pooled OR: 1.31, 95% CI: 1.05–1.64; pooled HR: 1.18, 95% CI: 1.02–1.36). Among studies which assessed depressive symptoms on continuous scales meta-analyses indicated an increased risk with every unit increase on the depressive symptoms scale (pooled OR: 1.06, 95% CI: 0.97–1.16; pooled HR: 1.06, 95% CI: 1.01–1.12).

Discussion Our review findings provide evidence that depression may be associated with an increased risk of hypertension. However, existing studies have important limitations and the substantial heterogeneity between studies included in two of the four meta-analyses remained unexplained after performing subgroup analyses. Before concluding that depression is indeed associated with an increased risk of hypertension, future prospective studies should improve the accuracy of exposure and outcome assessment, aim to take all major confounding and effect modifying factors into account, and present effect estimates for subgroups in order to help facilitate more meaningful meta-analyses of study findings. Further research is also needed to determine whether the observed association between depression and hypertension is causal.