The Efficacy Of Exercise In The Reduction Of Depressive Symptoms Across Serotonin Transporter Genotypes

Abstract

Exercise is effective in the alleviation of depressive symptoms and may have physiological effects similar to those of selective serotonin reuptake inhibitors (SSRIs). Recent research has begun to identify individual differences in response to treatment, such as the difference in treatment effects across genetic polymorphisms of the serotonin transporter polymorphic region (5-HTTLPR), which characterized by two alleles: long (l) and short (s). The l allele has been associated with a better response to SSRIs. PURPOSE:: To examine the antidepressant effects of exercise across 5-HTTLPR genotypes. METHODS: Participants, ages 18-23, were randomly assigned to a 5-week exercise intervention or a no-treatment control group. Participants completed the Beck Depression Inventory prior to and following the intervention and provided a saliva sample for DNA analysis. RESULTS: A mixed 2 × 2 (group × time) ANOVA revealed a significant interaction, F(1, 127) = 16.82, p <.01, indicating a significant reduction in depression in the exercise group compared to the control group. A mixed 3 × 2 × 2 (genotype × group × time) ANOVA was used to analyze the effect of exercise across 5-HTTLPR genotypes. The three-way interaction approached significance, F(1, 124) = 2.76, p = 0.067. However, the distribution of genotypes was not consistent across the treatment groups, putting the analysis at risk due to multicollinearity. To address this concern, the ls and ll genotypes were grouped together, due to their similar response to exercise. An additional 2 × 2 × 2 ANOVA revealed a significant three-way interaction, F(1, 124) = 4.836, p <.05, indicating that the effect of exercise varied across genotype. Follow-up tests revealed a significant reduction in depression symptoms in the ll/ls group compared to the ss group. CONCLUSIONS: The effects of exercise on depressive symptoms appear to be moderated by 5-HTTLPR genotype. When combined with previous research this suggests that the mechanisms responsible alleviation of depressive symptoms may be the same for exercise and SSRI treatment, thus strengthening the case for exercise as a legitimate treatment for depressive disorders. Furthermore, these findings suggest that 5-HTTLPR genotype should be a factor in determining the proper line of treatment for depression.