Sleep duration; general and abdominal obesity; and weight change among the older adult population of Spain

Nutrition Research Newsletter, March, 2008

Spain and other developed countries have witnessed an obesity epidemic during the past decades. This epidemic has important public health consequences because obesity is associated with numerous diseases and disability, greater use of health services, and shorter life expectancy. Because obesity treatments are of limited efficacy, the identification of new determinants of excess weight that could lead to preventive strategies is of the greatest interest. Among these new determinants, habitual sleep curtailment has recently received much attention.

In Western societies, obesity has raised in parallel with a decrease in hours of sleep, because of biological factors, such as sleep and other medical disorders, and because of behavioral and social factors, such as child care, shift-work, and round-the-clock entertainment. Experimental evidence in animals also shows that circadian rhythm is associated with obesity and metabolic dysfunction, as well as clinical evidence in humans that sleep debt has a harmful effect on carbohydrate metabolism and endocrine function. Epidemiologic studies on children and adolescents have shown a consistent and strong association between shorter sleep duration and greater frequency of both concurrent and future obesity. In adults, the results are less consistent, although a number of cross-sectional studies have reported that obesity is more frequent among those who sleep less.

This study examined the cross-sectional association between habitual sleep duration and general and abdominal obesity among the older adult population of Spain. In addition, it examined the longitudinal relation between sleep duration and short-term weight change. This prospective study was conducted from 2001 to 2003 on 3576 persons whose habitual sleep duration was self-reported in 2001. The outcomes were obesity [BMI; in kg/[m.sup.2]) 30], severe obesity (BMI 35), and abdominal obesity (waist circumference > 102 cm in men and >88 cm in women) in 2001 and weight gain 5 kg in the period 2001-2003.

Compared with subjects who slept 7 h, subjects who slept 5 h had a greater frequency of obesity and severe obesity. In addition, sleeping 8 h was associated with obesity and severe obesity. Similarly, subjects sleeping 9 h were more likely to have severe obesity. Among women, weight gain 5 kg was more frequent among subjects sleeping 5 h, 8 h, and 9 h. No association was observed between sleep duration and abdominal obesity.

In the present study, sleeping 5 h and sleeping 8 or 9 h were both associated with a weight gain of 5 kg in 2 y in women. Because these results proceed from a prospective follow-up, and because they are in line with results of the cross-sectional analysis, they reinforce the hypothesis that sleep duration is associated with obesity in the elderly. However, the researchers do not have an explanation for this association being observed only in women. Other researchers have observed sex differences in the study association, but participant's age ranged from 3 through 102 y and data were not disaggregated by age. In addition, present knowledge of the mechanisms for the association between sleep duration and obesity is insufficient to explain sex differences. Thus, the results on this particular issue should be confirmed in future studies.

Finally, although sleep duration was associated with general obesity, it showed no such association with abdominal obesity. This discrepancy may be linked to the different pathogenic mechanisms of each type of obesity. Among the elderly, the frequency of general obesity decreases with age, but the frequency of abdominal obesity remains stable or even increases. Moreover, the frequency of abdominal obesity was high in this cohort, so that the effect of sleep duration on abdominal obesity would have had to be marked to be discernible.

Among older adults, short as well as 8- and 9-h habitual sleep duration is associated with obesity and with short-term weight gain in women. However, no association was observed between sleep duration, abdominal obesity, and weight loss among older Spanish adults. Because this is one of the first studies on the older adult population, these results should be confirmed in future investigations. Moreover, the mechanisms of the relation between sleep duration and obesity in the elderly require further research.

E Lopez-Garcia, R Faubel, L Leon-Munoz, et al. Sleep duration, general and abdominal obesity, and weight change among the older adult population of Spain. AJCN; 87:310-316 (February 2008) [Correspondence: F Rodriguez-Artalejo, Departamento de Medicina Preventiva y Salud Publica, Facultad de Medicina, Universidad Autonoma de Madrid, C/ Arzobispo Morcillo, 2, 28029 Madrid, Spain. E-mail: fernando.artalejo@uam.es]