ORIGINAL ARTICLE Sleep length, working hours and socio-demographic variables are associated with time attending evening classes among working college students Roberta NAGAI-MANELLI, 1,3 Arne LOWDEN, 3 Claudia Roberta de CASTRO MORENO, 1 Liliane Reis TEIXEIRA, 2 Andréa Aparecida da LUZ, 1 Marina Hurga MUSSI, 1 Adriana Balian CONCEIÇÃO 1 and Frida Marina FISCHER 1 1 Department of Environmental Health, School of Public Health, University of São Paulo, São Paulo, 2 National School of Public Health, FIOCRUZ, Rio de Janeiro, Brazil, and 3 Stress Research Institute, Stockholm University, Stockholm, Sweden Abstract It is the aim of the present study to assess factors associated with time spent in class among working college students. Eighty-two working students from 21 to 26 years old participated in this study. They were enrolled in an evening course of the University of São Paulo, Brazil. Participants answered a questionnaire on living and working conditions. During seven consecutive days, they wore an actigraph, filled out daily activity diaries (including time spent in classes) and the Karolinska Sleepiness Scale every three hours from waking until bedtime. Linear regression analyses were performed in order to assess the variables associated with time spent in classes. The results showed that gender, sleep length, excessive sleepiness, alcoholic beverage consumption (during workdays) and working hours were associated factors with time spent in class. Thus, those who spent less time in class were males, slept longer hours, reported excessive sleepiness on Saturdays, worked longer hours, and reported alcohol consumption. The combined effects of long work hours (>40 h/week) and reduced sleep length may affect lifestyles and academic performance. Future studies should aim to look at adverse health effects induced by reduced sleep duration, even among working students who spent more time attending evening classes. Key words: college students, time spent in classes, work and study. INTRODUCTION Data from the Brazilian Institute of Geography and Sta- tistics 1 showed that in 2003, there were approximately 34 million people between 15 and 24 years old in Brazil. Among them, 64% were considered as workers. The data also suggested that, as they get older, the number of those who exclusively study decreases, whereas the number of those only working increases. There is also a third group, of those who both work and study, repre- senting around 25% of the young Brazilian population. Usually they are engaged in full-time jobs (daily Correspondence: Dr Roberta Nagai-Manelli, Stress Research Institute, Stockholm University, SE-106 91 Stockholm, Sweden. Email: roberta01@gmail.com Frida Marina Fischer supervised Roberta Nagai-Manelli in her doctoral program conducted at the School of Public Health, Dept Environmental Health, University of São Paulo, Brazil. Accepted 23 August 2011. Sleep and Biological Rhythms 2012; 10: 53–60 doi:10.1111/j.1479-8425.2011.00519.x 53 © 2011 The Authors Sleep and Biological Rhythms © 2011 Japanese Society of Sleep Research