Differences in sleep functioning between individuals with seasonal affective disorder and major depressive disorder in Finland.

BACKGROUND: Sleep problems are commonly reported in seasonal affective disorder (SAD) and major depressive disorder (MDD). However, the specific characteristics of sleep difficulties differ. Frequent sleep problems in MDD are insomnia and night awakenings, whereas SAD patients complain of hypersomnia and daytime sleepiness. No previous studies have reported differences in sleep functioning between these two disorders.

METHODS: We interviewed 4554 subjects from the Health 2011 survey and included 4153 individuals in this study. We selected participants who fulfilled the criteria for SAD (n = 223), nonseasonal-MDD (n = 238), SAD + MDD (n = 65), and controls (n = 3627). They completed the World Health Organization Composite International Diagnostic Interview, Munich version (M-CIDI), the Seasonal Pattern Assessment Questionnaire (SPAQ), The Beck Depression Inventory (BDI), the EuroQoL (EQ-5), the Alcohol Use Disorders Identification Test (AUDIT) and several questions about sleeping, based on the Basic Nordic Sleep Questionnaire (BNSQ).

RESULTS: We found Significant differences between groups for "enough sleep", "breathing interruptions during sleep", "tiredness during the day", and "sleeping difficulties". Controls reported better functioning in all sleep variables. SAD + MDD individuals showed more problems in "enough sleep" than SAD, more "breathing interruptions during sleep" than SAD and nonseasonal-MDD, felt more "tired during the day" than SAD and nonseasonal-MDD, and reported more "sleeping difficulties" than SAD and nonseasonal-MDD. Finally, nonseasonal-MDD individuals felt more "tired during the day" than SAD.

CONCLUSION: Individuals with SAD + MDD show generalized sleeping problems. However, when SAD and nonseasonal-MDD appear separately, similar sleep functioning is observed. Nonseasonal-MDD subjects report to be more tired during the day than SAD.