Circadian temperature and cortisol rhythms during a constant routine are phase-delayed in hypersomnic winter depression.
Level 4 - case-series / case-control
Small case-control comparison with non-randomized pre-post intervention assessment
PubMed 9146822 · doi:10.1016/S0006-3223(96)00210-7
What was done
Six female controls and six female patients with hypersomnic seasonal affective disorder (SAD) were evaluated under a 27-hour constant routine (bed rest and sleep deprivation) following 6 days of standardized sleep. Core rectal temperature, plasma cortisol, and thyroid-stimulating hormone (TSH) rhythms were measured in controls and in SAD patients before and after morning bright light treatment.
What was found
The fitted rectal temperature minimum was significantly phase-delayed in SAD patients compared to controls (5:42 AM vs. 3:16 AM, p < .005); following morning bright light treatment, it advanced to 3:36 AM (p = .06). The cortisol rhythm minimum was also phase-delayed in SAD patients compared to controls (12:11 AM vs. 10:03 PM, p < .05) and advanced to 10:38 PM post-treatment (p = .06). TSH acrophase was not statistically significantly phase-delayed compared to controls (trend p = .07) and showed a non-significant trend toward phase-advancing after light treatment (p = .09).
Why it matters
This study provides physiological evidence that hypersomnic winter depression involves a circadian phase delay relative to sleep, supporting the phase-shift hypothesis for the mechanism of morning bright light therapy.
Limits
The sample size is extremely small (N = 12 total, 6 per group) and restricted exclusively to females. The light treatment phase-shift effects were borderline non-significant (p = .06 to .09), and the study lacked a sham or randomized control group for the light intervention.
Cited by
- supports Studies published by Dr. Avery in the 1980s and 1997 demonstrated that individuals with depression often exhibit elevated nighttime body temperature and impaired thermoregulatory cooling.