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The discrepancy between biological and social rhythms known as social jetlag (SJL) is common in modern society and has a range of negative consequences for cognitive functioning, well-being and health. Social jetlag is typical for people with late chronotypes. As shown earlier, the prevalence of individuals with a late chronotype is higher among the residents of high latitudes. Therefore, a higher rate of detection of people with SJL should be expected in the North. In this study we assessed the detection rate of SJL among 62 young inhabitants of the European North of Russia (the Komi Republic), and the relationship between SJL, the circadian rhythm of the wrist temperature, and the cortisol awakening response (CAR). The detection rate of SJL was 65% among the people examined. A significant decrease in the amplitude (A) of circadian rhythm of wrist temperature: (β = -0.34 (CI 95%: -0.66 to -0.33); F1,60 = 10.4; p < 0.0001; η(2) = 0.31), an increased incidence of depression: No-SJL = 4.5%; SJL = 17.5% (H = 4.84; p < 0.05), and a tendency for an increase in CAR was also observed in the SJL group. There were sex differences in sensitivity to SJL. Females with SJL but not males had higher global seasonality scores (β = 0.51 (CI 95%: 0.21 to 0.81); F1,33 = 10.9; p < 0.002; η(2) =0.24), shorter sleep duration (β = -0.52 (CI 95%: -0.82 to -0.22); F1,33 = 12.9; p < 0.001; η(2) = 0.28), worse sleep quality (β = 0.39 (CI 95%: 0.07 to 0.72); F1,33 = 6.31; p < 0.017; η(2) = 0.16) and lower A of circadian rhythm of wrist temperature (β = -0.18 (CI 95%: -0.55 to 0.18); F1,33 = 4.48; p < 0.043; η(2) = 0.13) compared with females without SJL. Thus, our data indicate that 40 of 62 participants of investigation had social jetlag. A decrease of the amplitude of the circadian rhythm of the wrist temperature appears to be an objective marker of SJL. Social jetlag had a strong negative impact on females but not on males.

The aim of this study was to evaluate the effects of chronotype and social jetlag (SJL) on intelligence. Subjects were aged 14-25 years (n = 1008). A significant effect of intelligence on academic performance, as measured by the Raven's Standard Progressive Matrices test, was found (F = 11.75, P < 0.0001, η = 0.03). When SJL was less than 2 hours, the intelligence of people with late chronotype was found to be higher than that of subjects with early and intermediate chronotypes (F = 3.12, P < 0.05, η = 0.02). A negative effect of SJL on the results of intelligence testing was noted only in subjects with late chronotype (F = 2.61, P < 0.05, η = 0.02). Our data suggest that people with late chronotype have a higher level of intelligence, but these advantages disappear when SJL ≥2 hours.