Contents
A study showing the relationship between the duration and stability of circadian rhythms and the level of depression.
Introduction
It is known that the duration and stability of circadian rhythms in humans varies. Traditionally, the chronotypes of an owl (persons with a pronounced increased duration of the daily rhythm), a lark (persons with a pronounced reduced duration of the daily rhythm), a pigeon (persons with an approximate coincidence of the daily rhythm with astronomical days) and dysrhythmics (arrhythmics, persons with an unexpressed daily rhythm) are distinguished.
Larks wake up easily, fall asleep easily, the most productive time of the day for them is morning, in the evening they may feel tired. Owls are reluctant to go to sleep, tend to wake up late, the most productive time of day for them is evening or night, they may feel sleepy in the morning. Pigeons are intermediate between the two, with no major fluctuations in performance during the day, and no major inconvenience when going to bed or waking up late or early.
There is an assumption that the difference between them consists in the duration of the subjective daily rhythm, which is not exactly equal to the duration of the astronomical day. In larks this duration is less than 24 hours, in owls it is longer. The physiological reasons for this phenomenon are the subject of discussion.
According to the stability of rhythms, people, regardless of the chronotype, can be pronounced rhythmics, the regimen of which does not provide for fluctuations, they go to bed and get up at the same time, experiencing inconvenience when they are forced to change the regime, change time zones or switch to seasonal time; unexpressed rhythms, the regime of which can change depending on the circumstances without serious inconvenience, and arrhythmias, the regime of which depends little on the astronomical day and which experience inconvenience if it is necessary to obey a strict regime.
According to one hypothesis, the division of people into chronotypes is caused by evolutionary necessity — the flock needs awake observers, regardless of the time of day. Larks provided «duty» in the mornings, owls — at night, arrhythmics filled in the possible gaps in the «schedule». According to another hypothesis, a person belongs to unconditionally diurnal animals, night wakefulness is abnormal for him and indicates psychological health disorders, in particular, sleep disturbance.
Hypothesis
Since sleep disturbances are one of the clearest symptoms of depression, it was assumed that if the second hypothesis were true, there would be a correlation between an increased circadian rhythm and the severity of signs of depression.
Methods
To determine the severity of depression, the depression scale of the Research Institute named after N.N. Bekhterev, the questionnaire was developed at the Research Institute of Psychoneurology. Ankylosing spondylitis for the differential diagnosis of depressive states and conditions close to depression, for screening diagnostics in mass studies and for the purposes of preliminary, pre-medical diagnosis.
To determine the duration of circadian rhythms, we used our own scale, consisting of 9 questions:
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Subjective circadian rhythm duration scale
1. I wake up easily.
2. I fall asleep easily.
3. I get up on time without an alarm.
4. I prefer to do serious things in the morning, with a fresh mind.
5. On a working day, I turn on immediately, without overclocking.
6. On weekends I like to sleep longer.
7. I prefer to work at night.
8. I consider it common to run to a night shop for groceries.
9. I like to stay up late at a party.
Positive answers to questions 1-5 and negative answers to questions 6-9 indicate a reduced subjective circadian rhythm, the reverse answers indicate an extended one.
To determine the stability of circadian rhythms, we used our own scale, consisting of 11 questions:
Subjective circadian rhythm stability scale
1. I go to bed at the same time.
2. My appetite coincides with lunch time.
3. If I had to go to bed later than usual, then I will wake up, respectively, the same amount later.
4. If possible, I like to lie down after dinner.
5. During the holidays I go to bed and get up later than usual.
6. During the holidays, my routine changes.
7. It is easy for me to change lanes when changing time zones or changing to daylight saving time.
8. If I am tired, I can fall asleep at any time of the day.
9. If you don’t feel like sleeping, then I prefer to sit for an extra hour or two.
10. I can switch to a nocturnal lifestyle.
11. I can work on a floating schedule — sometimes during the day, sometimes at night.
Positive answers to questions 1,2 and negative answers to questions 3-11 indicate the stability of the subjective circadian rhythm, the reverse answers indicate instability.
3 questions of these scales had an intercorrelation from in the range of 0.5-0.7, 3 more questions of these scales had a correlation with 3 questions of the depression scale in the range of 0.5-0.7, 4 questions of the depression scale had an intercorrelation in the range of 0.5-0.7, for the remaining questions of the block, the pairwise correlation coefficients modulo were
A questionnaire composed of these three scales was presented to the respondents on the Internet.
The results
The sample consisted of 94 respondents aged 14 to 52, 32 men and 62 women.
A very weak positive (R=0.25) significant (p=.018) correlation was found between the duration of the subjective circadian rhythm and the level of depression.
A weak positive (R=0.4) significant (p=.0001) was found between the sum of the scales of the duration and stability of the subjective circadian rhythm (combination of the «owl» mode with arrhythmia) and the level of depression.
No correlation was found between the level of depression and arrhythmia alone (R=0.03, p=0.76), nor was there a correlation between the level of depression and the combination of early morning mode with arrhythmia (R=0.11, p=.27).
Removal of the Depression Scale #4 statement “I have a bad night’s sleep” did not affect the result (changes in the third or fourth decimal places).
Separately, a correlation was determined with the Depression Scale #4 statement, «I have a bad night’s sleep.» There is no correlation for the duration and stability scales of the subjective circadian rhythm (R=0.06, p=.5 and R=0.09, p=.0.4, respectively), for the combination of the «owl» mode and arrhythmia, a very weak positive (R=0.3) significant ( p=.004) correlation.
Conclusions
The combination of night owl mode with arrhythmia is symptomatically indistinguishable from sleep disorders, so despite the relatively higher correlation coefficient of this combination with the level of depression, the fact that only a slightly lower correlation was found for this combination with the Depression Scale #4 statement “I have a bad night sleep”, which has a correlation coefficient of R = 0.4 with the entire scale, while both factors separately do not have such a correlation, indicates the need to differentiate this combination and sleep disorders in order to draw any conclusions. In any case, the correlation is rather weak, and there is no apparent significance of such a question.
Judging by the results obtained, individual differences in the duration and stability of subjective circadian rhythms cannot be considered a deviation from the norm.
Long circadian rhythms may be considered a minor risk factor for depression.
In the future, it is necessary to investigate how the experience of the «owl» mode affects the likelihood of developing depression.