Longitudinal associations between number of cigarettes per day and depressive symptoms in adult smokers with type 2 diabetes: A path analysis approach

Objective: Three theoretical models describe the direction of the association between depressive symptoms and cigarettes per day (CPD) in smokers: 1) CPD predicts subsequent depressive symptoms, 2) depressive symptoms predict CPD, and 3) there is a bidirectional relation between CPD and depressive symptoms. The objective of the study was to compare the fit of these three theoretical models to data from a community-based sample of adults with type 2 diabetes (T2D) who smoke cigarettes.

Methods: Data were from adults with T2D who participated in the Evaluation of Diabetes Treatment Study. At baseline, 296 participants reported being a current smoker and were included in the analyses. Measures of CPD and depressive symptoms were collected annually over four years. Path models corresponding to the three directionality hypotheses were estimated. Model fit was compared, and the best fitting model was selected on the basis of Akaike's Information Criterion (AIC).

Results: The path model depicting a unidirectional association from CPD to subsequent depressive symptoms had the lowest AIC value (7110.94) and was thus identified as the best fitting model. Although some paths within the model did not meet conventional levels of statistical significance, in general, more CPD predicted higher levels of depressive symptoms at subsequent follow-up points.

Conclusion: Amongst smokers with T2D, a primary smoking model, in which smoking precedes depressive symptoms, may best explain the longitudinal association between CPD and depressive symptoms. These findings further justify the need for early smoking cessation in diabetes care.