Objective: To evaluate the prevalence of obesity and weight changes in night shift workers and their relationship with sleep. Methods: Fifty night shift and twenty-six day shift workers were evaluated. They belonged to one of two groups: nurse technicians/assistants or nurses. The night shift started at 7:00 p.m. and ended at 7:00 a.m., while the day shift was either from 7:00 a.m. to 1:00 p.m. or from 1:00 p.m. to 7:00 p.m. Data were collected using sleep diaries, personal questionnaires, scales to measure weight, and height measurement to calculate body mass index (BMI). Results: There were significant differences between the day shift and the night shift groups in sleep latency (6m54s and 20m6s; p<0.001), wakeup call (6h25m and 7h52m; p<0.001), sleep duration (7h12m and 8h21m; p=0.002), quality of nocturnal sleep (8.48 and 7.62; p=0.009), and total nap time (34m48s and 1h30m; p=0.001), respectively. The average BMI-1 (24.57; p=0.015) and BMI-2 (25.63; p=0.033) values from the day shift group were lower than those of the night shift group - BMI-1 (27.01) and BMI-2 (28.04). The frequency of physical activity was correlated with the difference in BMI (r=-0.296; p=0.0366). Conclusions: The night shift workers showed a higher average BMI than day shift workers did. However, it was not possible to ascertain whether sleep alterations influenced the weight gain of night shift workers.34125130Niedhammer, I., Lert, F., Marne, M.J., Prevalence of overweight and weight gain in relation to night work in a nurses' cohort (1996) Int J Obes Relat Metab Disord., 20 (7), pp. 625-633Costa, G., Shift work and occupational medicine: An overview (2003) Occup Med (Lond)., 53 (2), pp. 83-88Sharifian, A., Farahani, S., Pasalar, P., Gharavi, M., Aminian, O., Shift work as an oxidative stressor (2005) J Circadian Rhythms., 3, p. 15Waage, S., Moen, B.E., Pallesen, S., Eriksen, H.R., Ursin, H., Akerstedt, T., Shift work disorder among oil rig workers in the North Sea (2009) Sleep., 32 (4), pp. 558-565Vangelova, K., The effect of shift rotation on variations of cortisol, fatigue and sleep in sound engineers (2008) Ind Health., 46 (5), pp. 490-493Morikawa, Y., Nakagawa, H., Miura, K., Soyama, Y., Ishizaki, M., Kido, T., Effect of shift work on body mass index and metabolic parameters (2007) Scand J Work Environ Health., 33 (1), pp. 45-50Biggi, N., Consonni, D., Galluzzo, V., Sogliani, M., Costa, G., Metabolic syndrome in permanent night workers (2008) Chronobiol Int., 25 (2), pp. 443-454Crispim, C.A., Zalcman, I., Dáttilo, M., Padilha, H.G., Tufik, S., Mello, M.T., Relation between sleep and obesity: A literature review (2007) Arq Bras Endocrinol Metabol., 51 (7), pp. 1041-1049. , PortugueseWatanabe, M., Kikuchi, H., Tanaka, K., Takahashi, M., Association of short sleep duration with weight gain and obesity at 1-year follow-up: A large-scale prospective study (2010) Sleep., 33 (2), pp. 161-167. , Comment in: Sleep. 2010;33(2):143-4De Martino, M.M., Comparative study of sleep patterns in nurses working day and night shifts (2002) Rev Panam Salud Publica., 12 (2), pp. 95-100. , SpanishGeliebter, A., Gluck, M.E., Tanowitz, M., Aronoff, N.J., Zammit, G.K., Work-shift period and weight change (2000) Nutrition., 16 (1), pp. 27-29Antunes, L.C., Levandovski, R., Dantas, G., Caumo, W., Hidalgo, M.P., Obesity and shift work: Chronobiological aspects (2010) Nutr Res Rev., 23 (1), pp. 155-168Spiegel, K., Leproult, R., Van Cauter, E., Impact of sleep debt on metabolic and endocrine function (1999) Lancet., 354 (9188), pp. 1435-1439Gangwisch, J.E., Malaspina, D., Boden-Albala, B., Heymsfield, S.B., Inadequate sleep as a risk factor for obesity: Analyses of the NHANES I (2005) Sleep, 28 (10), pp. 1289-1296. , Comment in: Sleep. 2005;28(10):1217-20. Sleep. 2008;31(5):595-6Taheri, S., Lin, L., Austin, D., Young, T., Mingot, E., Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index (2004) PLoS Med., 1 (3), pp. e62Spiegel, K., Leproult, R., L'hermite-Balériaux, M., Copinschi, G., Penev, P.D., Van Cauter, E., Leptin levels are dependent on sleep duration: Relationships with sympathovagal balance, carbohydrate regulation, cortisol, and thyrotropin (2004) J Clin Endocrinol Metab., 89 (11), pp. 5762-5771Spiegel, K., Tasali, E., Penev, P., Van Cauter, E., Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite (2004) Ann Intern Med., 141 (11), pp. 846-850. , Comment in: Ann Intern Med. 2004;141(11):885-6. Ann Intern Med. 2004;141(11):152Knutson, K.L., Spiegel, K., Penev, P., Van Cauter, E., The metabolic consequences of sleep deprivation (2007) Sleep Med Rev., 11 (3), pp. 163-178. , Comment in: Sleep Med Rev. 2007;11(3):241-3author reply 244-7. Sleep Med Rev. 2007;11(3):159-62Fernandez, A.C., Mello, M.T., Tufik, S., Castro, P.M., Fisberg, M., Influência do treinamento aeróbico e anaeróbico na massa de gordura corporal de adolescentes obesos (2004) Rev Bras Med Esporte., 10 (3), pp. 152-164Monteiro, R.C.A., Riether, P.T.A., Burini, R.C., Efeito do programa misto de intervenção nutricional e exercício físico sobre a composição corporal e os hábitos alimentares de mulheres obesas em climatério (2004) Rev Nutr., 17 (4), pp. 479-489Flores, M.B.S., (2006) Papel da leptina e insulina na PI3 quinase/AKT em hipotálamo de ratos submetidos a exercício físico [tese], , Campinas: Universidade Estadual de CampinasDe Martino, M.M.F., (1996) Estudo da variabilidade circadiana da temperatura oral, do ciclo vigília-sono e de testes psicofisiológicos de enfermeiras em diferentes turnos de trabalho [tese], , Campinas: Universidade Estadual de Campinas;Fischer, F.M., Moreno, C.R., da Silva Borges Notarnicola, F., Louzada, F.M., Implementation of 12-hour shifts in a Brazilian petro-petrochemical plant: Impact on sleep and alertness (2000) Chronobiol Int., 17 (4), pp. 521-537Stampi, C., (1996) Cochilos e padrões polifásicos do sono humano, pp. 392-411. , In: Reimão R. Sono: estudo abrangente. São Paulo: AtheneuKnutson, K.L., Van Cauter, E., Associations between sleep loss and increased risk of obesity and diabetes (2008) Ann N Y Acad Sci., 1129, pp. 287-304