Fasting glucose and the risk of depressive symptoms: Instrumental-variable regression in the Cardiovascular Risk in Young Finns Study

: Wesołowska K, Elovainio M, Hintsa T, Jokela M, Pulkki-Råback L, Pitkänen N, Lipsanen J, Tukiainen J, Lyytikäinen LP, Lehtimäki T, Juonala M, Raitakari O, Keltikangas-Järvinen L

Publisher: Springer

: 2017

: International Journal of Behavioral Medicine

: IJBM

: 24

: 6

: 901

: 907

: 7

: 1070-5503

DOI: https://doi.org/10.1007/s12529-017-9639-2

: https://www.ncbi.nlm.nih.gov/pubmed/28779468

PURPOSE: Type 2 diabetes (T2D) has been
associated with depressive symptoms, but the causal direction of this
association and the underlying mechanisms, such as increased glucose
levels, remain unclear. We used instrumental-variable regression with a
genetic instrument (Mendelian randomization) to examine a causal role of
increased glucose concentrations in the development of depressive
symptoms. METHOD: Data were from the population-based
Cardiovascular Risk in Young Finns Study (n = 1217). Depressive symptoms
were assessed in 2012 using a modified Beck Depression Inventory
(BDI-I). Fasting glucose was measured concurrently with depressive
symptoms. A genetic risk score for fasting glucose (with 35 single
nucleotide polymorphisms) was used as an instrumental variable for
glucose. RESULTS: Glucose was not associated with
depressive symptoms in the standard linear regression (B = -0.04, 95% CI
[-0.12, 0.04], p = .34), but the instrumental-variable regression
showed an inverse association between glucose and depressive symptoms
(B = -0.43, 95% CI [-0.79, -0.07], p = .020). The difference between the
estimates of standard linear regression and instrumental-variable
regression was significant (p = .026). CONCLUSION: Our results suggest
that the association between T2D and depressive symptoms is unlikely to
be caused by increased glucose concentrations. It seems possible that
T2D might be linked to depressive symptoms due to low glucose levels.