Beran M, Muzambi R, Geraets A, et al. - According to this systematic review and meta-analysis, there was an existence of a bidirectional longitudinal relationship between depressive symptoms and HbA _1c. The observed effect sizes, however, were small, and further research in large-scale longitudinal studies is required to confirm this association. The findings could have clinical implications because depressive symptoms and HbA _1c levels could be targeted at the same time in the prevention and treatment of diabetes and depression.

• One thousand six hundred forty-two studies were retrieved; 26 studies were included in the systematic review and eleven in the meta-analysis.

• The majority of the studies (16/26) concentrated on type 2 diabetes.

• The quality of the study was rated as good (n = 19), fair (n = 2), and poor (n = 5).

• Six of the meta-analysed studies looked at the longitudinal relationship between self-reported depressive symptoms and HbA _1c, and five looked at the reverse longitudinal relationship, with a total sample size of n = 48,793 and a mean follow-up of 2 years.

• Higher levels of baseline depressive symptoms were linked to subsequent higher levels of HbA _1c.

• Higher baseline HbA _1c levels were also linked to an 18% increased risk of (probable) depression.