Despite the link that risk factors, such as early-life stressors and genetic polymorphisms, have with the development of depressive symptoms, not every individual who is 'at risk' develops this disorder. It has been suggested that lifestyle factors, such as diet and exercise, may play a critical role in this regard. To date, there have been few reports examining the interactions between these lifestyle factors and other risk factors in promoting depressive features. The purpose of the present investigation was to assess the moderating effects of dietary pattern and exercise frequency, in the relations between stressors experienced early in life and psychological outcomes (depressive symptoms and creative problem solving), as well as current stressors and a biological outcome (cortisol response). In addition, the present investigation sought to examine whether these lifestyle variables might interact with immune related gene mutations, in predicting depressive symptoms and other related measures (executive functioning, coping flexibility, and coping endorsement), as both depression and these lifestyle factors are related to immune functioning.
In Study 1 (N=278), physical trauma was negatively related to performance on the Remote Associates Test, a measure of creative problem solving, but this relation only existed for individuals who consumed smaller amounts of healthy foods. It was also found that sexual trauma was positively related to depressive symptoms, but this relation was stronger among participants who consumed greater amounts of unhealthy foods. Study 2 (N=163) demonstrated that dietary patterns interact with immune related genetic polymorphisms and sex, in predicting depressive symptoms, coping flexibility, and coping strategy endorsement. Building upon the findings of the previous study, Study 3 (N=144) indicated that diet and exercise interacted with immune related polymorphisms and sex, in predicting performance on the Iowa Gambling Task (a measure of executive functioning). Finally, Study 4 (N=81) showed that adherence to an unhealthy dietary pattern was associated with elevated levels of cortisol in response to the Trier Social Stress Test. Together, these studies suggest that dietary pattern and exercise habits, can interact with stressors (both current and past) and immune related polymorphisms, in predicting risk for depression.