Chronotype-Dependent Changes in Sleep Habits Associated with Dim Light Melatonin Onset in the Antarctic Summer

Abstract

Dim light melatonin onset (DLMO) is the most reliable measure of human central circadian timing. Its modulation by light exposure and chronotype has been scarcely approached. We evaluated the impact of light changes on the interaction between melatonin, sleep, and chronotype in university students (n = 12) between the Antarctic summer (10 days) and the autumn equinox in Montevideo, Uruguay (10 days). Circadian preferences were tested by validated questionnaires. A Morningness–Eveningness Questionnaire average value (47 ± 8.01) was used to separate late and early participants. Daylight exposure (measured by actimetry) was significantly higher in Antarctica versus Montevideo in both sensitive time windows (the morning phase-advancing and the evening phase-delaying). Melatonin was measured in hourly saliva samples (18–24 h) collected in dim light conditions (<30 lx) during the last night of each study period. Early and late participants were exposed to similar amounts of light in both sites and time windows, but only early participants were significantly more exposed during the late evening in Antarctica. Late participants advanced their DLMO with no changes in sleep onset time in Antarctica, while early participants delayed their DLMO and sleep onset time. This different susceptibility to respond to light may be explained by a subtle difference in evening light exposure between chronotypes.

Early chronotype with advanced activity rhythms and dim light melatonin onset in a rural population

“…DLMO for the Baependi population (mean is marked with red dotted line) compared with published DLMO data from other adult populations. [ 5 ] 9,28‐30,32,35‐42 Data are presented as mean ± SEM. Different methodologies for determining DLMO are shown as follows: dynamic threshold refers to defining DLMO based on two standard deviations above the mean of three or more prerise values or from parameters describing a fitted curve to the time series of melatonin samples.…”

Short Sleep Duration and Extremely Delayed Chronotypes in Uruguayan Youth: The Role of School Start Times and Social Constraints

“…The Uruguayan school system appears as particularly advantageous for chronobiological studies because students are randomly assigned into shifts, creating a natural experiment to compare between similar populations under different social pressures (Estevan et al, 2018). The chronotype distribution of Uruguayan high school students reported in this study (as well as in Uruguayan university students; Silva et al, 2019;Tassino et al, 2016) is extremely delayed, with some of the most extreme late chronotype values reported so far in the literature (Carissimi et al, 2016;Fischer et al, 2017;Masal et al, 2015Masal et al, , 2016Pande et al, 2018;Porcheret et al, 2018;Randler, 2008;Randler et al, 2009;Roenneberg et al, 2007a;Vollmer et al, 2017). It is noteworthy that late chronotypes have also been reported in students from countries with very similar cultural practices such as Buenos Aires (Argentina) or Madrid (Spain) (Randler, 2008).…”

Relationship between circadian rhythm characteristics and chronotypes with multiple sclerosis: literature review

“…Chro no ti pai skirs to mi á tris pa grin di nes gru pes, ið skiriant ry ti ná ti pà (bû din gas ið reikð tas no ras ei ti mie go ti ir kel tis anks ti ry te; di dþiau siu pro duk ty vu mo lai ko tar piu ávar di jant ry tà), va ka ri ná ti pà (ei na ma mie go ti la bai vë lai va ka re ar ba net po vi dur nak èio ir ke lia ma si ati tin ka mai vëliau -vë lai ry te ar ba die nà; pro duk ty viau sias die nos lai kotar pis daþ niau siai bû na po pie të) ir tar pi ná, pa tá daþ niau sià ti pà (ðá chro no ti pà tu ri apie 60 % po pu lia ci jos), ku riam bûdin ga ry ti niø ir va ka ri niø ti pø sam plai ka [12,13].…”

“…Vis dël to ryð ki ðvie sa va ka re ga li slo pin ti nak tinae me la to ni no ga my bà, to dël itin svar bu ðio hor mo no koncen tra ci jà ma tuo ti blan kios ðvie sos ap lin ko je. Vë les në mela to ni no ið si sky ri mo pra dþia reikð min gai sie ja si su ati dë ta cir ka di ne fa ze, taip pat su va ka ri niu chro no ti pu [11,13,17];…”