Energy drink consumption and depressive symptoms in Iceland: associations with season and circadian preference

Abstract Background Energy drinks are among the fastest-growing segments of the global beverage market, and their consumption is increasingly recognised as a public health concern, especially given their associations with sleep disturbances and depressive symptoms. These outcomes are also associated with circadian preference, a proxy for chronotype, and seasonal variation in daylight. Evening types tend to report higher levels of insomnia and depressive symptoms and consume energy drinks more frequently, while reduced daylight in autumn and winter is similarly associated with poorer sleep and mood. Yet no study has examined how energy drink intake, circadian preference, and seasonal variation jointly relate to insomnia and depressive symptoms across seasons, or whether such associations are specific to energy drinks rather than coffee. Iceland, with its extreme seasonal variation in daylight, offers a unique setting to study these associations. Methods An Icelandic adult sample (baseline N = 281) completed self-report measures across four seasons, comprising the Food Frequency Questionnaire (energy drink and coffee intake frequency), the Morningness–Eveningness Questionnaire (circadian preference), the Bergen Insomnia Scale, and the Depression Anxiety Stress Scales depression subscale. Cross-sectional associations were examined using multiple linear regression, and longitudinal associations were examined using linear mixed-effects models. Results Energy drink intake frequency was associated with insomnia cross-sectionally, although this association did not survive correction for multiple comparisons; coffee showed no association with insomnia at either stage. Longitudinally, both energy drink and coffee intake frequency showed interactions with autumn and circadian preference in predicting depressive symptoms before correction; however, only the energy drink × autumn interaction survived correction for multiple comparisons. The seasonal energy drink effect appeared more pronounced among evening types before correction, although this chronotype-specific pattern did not remain significant after correction. A supplementary categorical analysis provided additional support for a possible chronotype-specific pattern. Conclusions Energy drink intake frequency showed a stronger association with depressive symptoms in autumn than in summer, a pattern not observed for coffee. Although the primary analyses did not provide statistically robust evidence for a chronotype-specific effect after correction, supplementary categorical findings suggest that evening types who frequently consume energy drinks may warrant further investigation, particularly during periods of rapid seasonal decline in daylight. These findings underscore the importance of considering circadian preference and seasonal context when examining associations between energy drink consumption and mental health, and support continued public health attention to this area.