Ecology of sleep and circadian phenotypes of the Brazilian population

Daniel Vartanian

University of São Paulo

2023-11-16

Hello, there 👋

This presentation will provide an overview of the thesis objectives, main concepts, methods, and results. Here is our itinerary.

1. Object and objectives
2. Introduction to the main concepts

1. Biological rhythms and complexity
2. Temporal phenotypes (AKA chronotypes)
3. Zeitgebers and the entrainment phenomenon
4. The two process of sleep regulation and the MCTQ
5. The latitude hypothesis

3. Thesis outline
4. Materials and methods
5. Main results
6. Discussion
7. Final remarks

Object and objectives

This thesis focuses on the ecology of sleep and circadian phenotypes (chronotypes) with the aim of providing answers to the following questions:

Q1. How are the sleep-wake cycles and circadian phenotypes of the adult Brazilian population characterized?

Q2. Is latitude associated with the regulation of circadian rhythms in humans?

The primary objectives (PO) are as follows:

PO1. Quantitatively describe the expression of sleep-wake cycles and circadian phenotypes of the Brazilian adult population at the end of the year 2017 (pre-pandemic).

PO2. Investigate and model the presence/absence of a significant association and effect between decimal degrees of latitude (independent variable (IV)) and circadian phenotypes (dependent variable (DV)) of the Brazilian population.

Methods and hypothesis

• Problem approach method: Hypothetico-deductive method (Popper, 1979)
• Procedure method: Statistical methods

The basic hypothesis to be tested is that populations residing near the equator (latitude 0°) have, on average, a shorter/more morning-oriented circadian phenotype compared to populations living near the Earth’s poles (Hut et al., 2013; Leocadio-Miguel et al., 2014, 2017; Pittendrigh et al., 1991; Randler, 2008; Randler & Rahafar, 2017; Roenneberg et al., 2003).

\[ \begin{cases} \text{H}_{0}: \text{R}^{2}_{r} >= \text{R}^{2}_{f} \\ \text{H}_{a}: \text{R}^{2}_{r} < \text{R}^{2}_{f} \end{cases} \]

\[ f^{2} = \cfrac{\text{R}^{2}_{f} - \text{R}^{2}_{r}}{1 - \text{R}^{2}_{f}} = \cfrac{\text{Additional Var. Explained}}{\text{Var. unexplained}} \]

Complex systems

• “Systems that don’t yield to compact forms of representation or description” (David Krakauer apud Mitchell (2013))
• “A system of many interacting parts where the system is more than just the sum of its parts” (Mark Newman apud Mitchell (2013))
• Systems with many connected agents that interact and exhibit self-organization and emergence behavior, all without the need for a central controller (adapted from Camilo Rodrigues Neto’s definition, supervisor of this thesis)
• Dialectics at its finest (my working definition)

Methods

• Problem approach method: Hypothetico-deductive method (Popper, 1979)
• Procedure method: Statistical methods

flowchart LR
  A[P1] --> B(TT)
  B --> C[EE]
  C --> D[P2]

Hypothesis test

The main idea of nested models is to verify the effect of the inclusion of one or more predictors in the model variance explanation (i.e., the \(\text{R}^{2}\)) (Allen, 1997). This can be made by creating a restricted model and then comparing it with a full model. Hence, the hypothesis can be schematized as follows.

\[ \begin{cases} \text{H}_{0}: \text{R}^{2}_{r} >= \text{R}^{2}_{f} \\ \text{H}_{a}: \text{R}^{2}_{r} < \text{R}^{2}_{f} \end{cases} \]

\[ f^{2} = \cfrac{\text{R}^{2}_{f} - \text{R}^{2}_{r}}{1 - \text{R}^{2}_{f}} = \cfrac{\text{Additional Var. Explained}}{\text{Var. unexplained}} \]

Restricted model (\(r\))

\[ \text{MSF}_{\text{sc}} = \beta_{0} + \beta_{1} \text{Sex} + \beta_{2} \text{Age} + \varepsilon \]

Full model (\(f\))

\[ \text{MSF}_{\text{sc}} = \beta_{0} + \beta_{1} \text{Sex} + \beta_{2} \text{Age} + \beta_{3} \text{Latitude} + \varepsilon \]

Elegibility criteria

Inclusion criteria

IC1. Residents in Brazil

IC2. Adults (i.e., age \(\geq\) 18 years)

IC3. Literate

IC4. With internet access

Exclusion criteria

None (besides validation)

Population

According to the Continuous National Household Sample Survey (PNAD), in 2017, Brazil had an illiteracy rate of \(6.9\%\) among individuals aged 18 years or older (Instituto Brasileiro de Geografia e Estatística, n.d.-c).

In that same year, the Brazilian population in this age group comprised approximately \(151,321,000\) individuals (Instituto Brasileiro de Geografia e Estatística, n.d.-b). Considering these two pieces of data, it can be inferred that there were around \(140,879,851\) literate individuals aged 18 years or older in Brazil in 2017.

According to the PNAD, the proportion of men and women above 18 years old in 2017 was \(48.163\%\) and \(51.837\%\), respectively (Instituto Brasileiro de Geografia e Estatística, n.d.-a). Another edition of the same study showed that internet usage covered \(82.17\%\) of Brazilian households in 2019 (Instituto Brasileiro de Geografia e Estatística, 2021). Based on this data, it is estimated that the size of the population to be represented in this study is around \(115,760,973\) individuals, which corresponds to approximately \(76.500\%\) of the adult Brazilian population in 2017.

Sample (raw) characteristics

• Convenience sample (non-probabilistic)
• Unit of observation and analysis: Individuals
• Total of \(120,265\) entries in the raw state
• \(118,068\) responses within a seven-day window (from 15th to 21st October 2017)
• Encompasses all states of Brazil
• \(92,107\) Brazilian resident subjects aged 18 years or older (\(78.012\%\) of the total) (ages between \(18-79\) years; mean of \(32.726 \pm 10.176\) years)
• \(66.320\%\) are female (ages between \(18-79\) years; mean of \(32.543 \pm 10.259\) years) and \(33.600\%\) are male (ages between \(18-79\) years; mean of \(33.076 \pm 9.987\) years)
• It is assumed that individuals in the sample are literate and have internet access, as it would not be possible to respond to the questionnaire without these characteristics.

Dataset characteristics

• \(120,265 entries\), divided into \(94\) variables, representing a total of \(11,304,910\) data points.
• All fields in the form were mandatory.
• The value of minutes in the collected times was obtained through intervals of \(5\) or \(10\) minutes.
• As it was a prototype, the collection form did not contain response validation rules for most fields, which resulted in a variety of formats in some of the collected variables.

Data categories

Record/Control

• id
• timestamp
• track

Personal

• Name
• Email
• Sex
• Date of birth
• Country of residence
• State of residence
• City of residence
• Residential ZIP code
• […]

Health

• Use of sleeping medication
• Use of other types of medication
• Presence of sleep disorders

Data categories

Habits

• Employment status
• Student status
• Work periods
• Study periods

MCTQ standard version

(workdays days and work-free days)

• Number of workdays per week
• Local time of going to bed
• Local time of preparing to sleep
• Sleep latency or time to fall asleep after preparing to sleep

• Local time of sleep end
• Use of alarm clock to wake up
• Time that it takes to get up after sleep end
• Light exposure

Data plan

See: https://dmphub.cdlib.org/dmps/doi:10.48321/D1DW8P

Research compendium

See:

• https://www.tandfonline.com/doi/abs/10.1080/00031305.2017.1375986.
• https://github.com/danielvartan/mastersthesis

Local time of the sleep corrected midpoint between sleep onset and sleep end on work-free days (MSF_sc), MCTQ proxy for measuring the chronotype, statistics of sample subjects.

name	value
n	79198
n_rm_na	79198
n_na	0
mean	04:28:17.770957
var	08:05:53.49992
sd	01:26:51.406096
min	00:22:30
q_1	03:26:25.714286
median	04:20:42.857143
q_3	05:25:42.857143
max	08:31:04.285714
iqr	01:59:17.142857
skewness	0.284586184927996
kurtosis	2.77321491178072

Residential geographic distribution among sample subjects.

Age pyramid of the sample subjects.

Relation between age and chronotype, divided by sex. Chronotype is represented by the local time of the sleep corrected midpoint between sleep onset and sleep end on work-free days (MSF_sc), MCTQ proxy for measuring the chronotype. The gray line represents both sex. Vertical lines represent the standard error of the mean (SEM).

Distribution of the local time of the sleep corrected midpoint between sleep onset and sleep end on work-free days (MSF_sc), MCTQ proxy for measuring the chronotype. The categorical cut-offs follow a quantile approach going from extremely early (\(0 |- 0.11\)) to the extremely late (\(0.88 - 1\)).

Correlation matrix of main variables.

Local time of the sleep corrected midpoint between sleep onset and sleep end on work-free days (MSF_sc), MCTQ proxy for measuring the chronotype, statistics of sample subjects.

name	value
n	76744
n_rm_na	76744
n_na	0
mean	04:28:35.437224
var	12:15:36.924895
sd	01:26:44.549637
min	00:22:30
q_1	03:26:47.142857
median	04:21:25.714286
q_3	05:26:04.285714
max	08:31:04.285714
iqr	01:59:17.142857
skewness	0.284161285620669
kurtosis	2.77330246940943

Distribution of mean aggregates of the local time of the sleep corrected midpoint between sleep onset and sleep end on work-free days (MSF_sc), MCTQ proxy for measuring the chronotype, in relation to latitude decimal degree intervals. Higher values of MSF_sc indicate a tendency toward a late chronotype. The red line represents a linear regression, and the shaded area indicates a pointwise 95% confidence interval.

Discussion

A significant p-value (\(\text{p-value} = 2e-16\)) was found, but with a negligible effect size (Cohen’s \(f^2 = 0.00740\)). Based on these results, we must reject \(\text{H}_{a}\) in favor of \(\text{H}_{0}\).

\[ \begin{cases} \text{H}_{0}: \text{R}^{2}_{r} >= \text{R}^{2}_{f} \\ \text{H}_{a}: \text{R}^{2}_{r} < \text{R}^{2}_{f} \end{cases} \]

It is then possible to answer one of the study main question: Is latitude associated with the regulation of circadian rhythms in humans? Based on these results the answer is no.

Discussion

Despite the lack of evidence, is not uncommon to hear talks insisting that the latitude effect is real and already confirmed, but, at this time, at least in humans, no empirical evidence can support this claim.

The results show that even with a wide latitudinal spectrum and with a big and aligned sample of biological states the latitude effect does not reveal itself in a non-negligible size.

As Karl Popper said, science begins and ends with questions (Popper, 1979). The absence of a strong entrainment with the solar zeitgeber shows that the entrainment phenomenon is more complex than we previously imagined. Other hypotheses for the human circadian entrainment, like the entrainment to self-selected light, proposed by Anna Skeldon and Derk-Jan Dijk (2021), need to be tested and may produce significant results.

{visibility=“hidden”} # IDK

Final remarks

This thesis was presented to the School of Arts, Sciences and Humanities (EACH) at the University of São Paulo (USP), as a requirement for the degree of Master of Science by the Graduate Program in Complex Systems Modeling (PPG-SCX).

Financial support was provided by the Coordination for the Improvement of Higher Education Personnel (CAPES (Grant number: 88887.703720/2022-00).

Thesis Supervisor: Prof. Dr. Camilo Rodrigues Neto.

Area of concentration: Fundamentals of complex systems.

You can learn more about this work at: https://github.com/danielvartan/mastersthesis

References

In accordance with the American Psychological Association (APA) Style, 7th edition.

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