Sleep and light exposure across different levels of urbanisation in Brazilian communities

Abstract

Quilombos are settlements originally founded by Africans and African descendants (Quilombolas) in remote parts of Brazil to escape slavery. Due to individual histories, Quilombos nowadays exhibit different states of industrialisation, making them ideal for studying the influence of electrification on daily behaviour. In a comparative approach, we aimed to understand whether and how human sleep changes with the introduction of artificial light. We investigated daily rest-activity-rhythms and sleep-patterns in the Quilombolas' by both wrist actimetry and the Munich ChronoType Questionnaire (MCTQ; the results of these two instruments correlated highly). Seven communities (MCTQ: N = 213/actimetry: N = 125) were compared in this study. Light exposure, phase of activity, sleep timing and duration differ across communities with various levels of urbanisation and histories of access to electricity. People living without electricity and those, who acquired it only very recently on average sleep earlier than those in more urbanised communities (mid-sleep about 1 hour earlier); sleep duration tends to be longer. Our results and those of others show that use of electricity and modern lifestyles have changed sleep behaviour. To understand the consequences of these changes for health, further studies are warranted.

Figure 1

Studied Quilombos in the South of Brazil. Peixoto dos Botinhas (PB–Viamão, RS), São Roque (SR–Praia Grande, SC), Morro do Fortunato (MF–Garopaba, SC), Mamãs (MM–Castro, PR), Bombas (BB–Iporanga, SP), Areia Branca (AB–Bocaiúva do Sul, PR), Córrego do Franco (CF–Adrianópolis, PR). Maps created using Mapbox TileMill (v. 0.10.1).

Figure 2

Average light profiles: each graph shows the average light profile of a community, calculated using individuals actimetry data. A comparison between the extremes, Bombas (BB) and Peixoto dos Botinhas (PB) can be seen at the bottom, being the graph to the right log scaled. Backgrounds represent photoperiod length (on the longest and shortest day). n = 11–27. BB: Bombas, AB: Areia Branca, SR: São Roque, CF: Córrego do Franco, MM: Mamãs, MF: Morro do Fortunato, PB: Peixoto dos Botinhas.

Figure 3

Light exposure: dots represent the median, whiskers represent interquartile ranges of light exposure during photoperiod (Kruskal-Wallis, χ²(6) = 11.95, p = 0.06) and after dusk (Kruskal-Wallis, χ² (6) = 50.96, p < 0.0001). Dots are colour coded according to the geographical isolation index. The greener the bar, the more geographically isolated the community. Dunn’s test adjusted p-values: ^*p < 0.05; ^**p < 0.01; ^***p < 0.001; ^****p < 0.0001). n = 11–27. BB: Bombas, AB: Areia Branca, SR: São Roque, CF: Córrego do Franco, MM: Mamãs, MF: Morro do Fortunato, PB: Peixoto dos Botinhas.

Figure 4

Centre of Gravity of Activity: dots represent the mean, whiskers represent the standard deviation. Dots are colour coded according to the geographical isolation index. The greener the bar, the more geographically isolated the community. The dotted line marks BB mean as a reference. ANOVA, F_(6,118) = 4.40, p < 0.001. Tukey’s adjusted p-values: ^*p < 0.05; ^**p < 0.01. n = 11–27. BB: Bombas, AB: Areia Branca, SR: São Roque, CF: Córrego do Franco, MM: Mamãs, MF: Morro do Fortunato, PB: Peixoto dos Botinhas.

Figure 5

Sleep timing and duration: (a) ‘Brushed’ lines represent average sleep episodes calculated from actimetry data. Horizontal whiskers represent standard deviation and triangles mid-sleep. Episodes are colour-coded according to the geographical isolation index. The greener the bar, the more geographically isolated the community. The dotted line marks BB mid-sleep mean as a reference. Sleep onset: ANOVA F_(6,118) = 6.88, p < 0.0001, mid-sleep: ANOVA F_(6,118) = 5.09, p < 0.001, wake-up: ANOVA F_(6,118) = 3.36, p < 0.01, sleep duration: ANOVA F_(6,118) = 6.54, p < 0.0001. (b) Tukey’s adjusted p-values: ^*p < 0.05; ^**p < 0.01; ^***p < 0.001; ^****p < 0.0001, ^#p < 0.15). n = 11–27. BB: Bombas, AB: Areia Branca, SR: São Roque, CF: Córrego do Franco, MM: Mamãs, MF: Morro do Fortunato, PB: Peixoto dos Botinhas.