A reader asks:

Is there any correlation between core body temperature and SAD? I have noticed that my body temperature drops markedly when experiencing depression during the fall.


Body Temp in SAD and Depressed Patients the Same

A simple question with a complicated answer — sorry about that! Depressed patients often report feeling colder than when they are well. Investigators have measured core body temperature in SAD patients in both winter and summer. They have also compared patients with non-depressed control subjects in both seasons. Puzzlingly, they have found no differences, or even elevated temperatures in the patients.

Body Temp Variation

However, there is a possible explanation for your observation: come fall, the circadian rhythm of the body temperature may start to shift later. Normally, temperature is higher during the day than in the late evening and night. For someone who usually wakes up at 6:00 a.m., nighttime temperature gradually declines until about 3:30 a.m., at which point it starts rising toward daytime levels even before you wake up.

Variation Due to Time of Year

In SAD, the time of the temperature minimum may shift substantially later in the fall and winter, to about 5:30 a.m. Therefore, if you were to take your temperature at 6 a.m. during the dark months, it would probably be lower than when you take it at 6 a.m. in the summer. As sunrise moves earlier in the spring — this can be simulated by morning light therapy in the fall and winter — the internal circadian clock shifts the temperature cycle back to its summertime state.