Despite the recent advances made in the arena of obesity and its links to sleep deprivation, significant knowledge gaps remain in place and continue to hinder the application of public health’s understanding of this issue to real-world problems. While there is not a single study in the literature in which the authors have examined the relationship between sleep deprivation and obesity and failed to report a significant association, there is significant confusion as to the direction (or even as to the existence) of causality between the independent and dependant variables.
One study’s authors report that “there was a dose dependent decrease in the proportion of overweight and obese children by duration of sleep” (von Kries, Toschke, Wurmser, Sauerwald, & Koletzko, 2002, p.714). Dose-response mechanisms are one of the primary qualities for which one should look when determining the level of causality according to the Bradford Hill criteria (Friedman, 2005). However, the same study later reveals that “reduced sleep might at least possibly be rather a consequence of overweight and obesity than its cause,” noting as a potential reason the fact that “exercise may account for better and longer sleep;” a problematic interaction in terms of determining causality because exercise is also known to be independently associated with weight loss (von Kries et al., 2002, p.714).
This same uncertainty is echoed in nearly every article in the literature. Another study’s authors conclude a discussion of the effects of changes in ghrelin and leptin levels on BMI by writing that “these changes can be hypothesized to play a contributory rather than compensatory, role in the development of overweight and obesity with sleep restriction” (Taheri, Lin, Austin, Young, & Mignot, 2004, p.214). Two additional studies strongly suggest the need for additional research into the relationship between the independent variable and the dependent variables (Vorona, Winn, Babineau, Eng, Feldman, & Ware, 2005; Spiegel, Tasali, Penev & Van Cauter, 2004).
Jennifer Altman concludes her summary of a conference in Neuroendocrinology with the assertion that “As ghrelin and leptin have such a broad palette of actions, it is not surprising that so many conundrums and paradoxes remain in this young field”
(2002, p.135). Now that we have a rudimentary understanding of the interaction between sleep deprivation, leptin, ghrelin, and BMI, the field is ready for a more rigorous study of the phenomenon at hand.
Public health and the associated medical fields have only recently begun to examine the relationship between sleep deprivation and overweight and obesity. Because the prevalence of overweight and obesity has increased so dramatically in the past 15 years (Bass & Turek, 2005), and because the consequences of this epidemic are so severe, including complications such as “insulin resistance and type 2 diabetes mellitus, hyperlipidemia, cardiovascular disease, hypertension, stroke, cancer, and arthritis” (Bass & Turek, 2005, p.15), much focus has been placed on overweight and obesity in the scientific literature. However, before the year 2000, most of this research examined sleep deprivation as a potential confounder or mediating variable in other relationships (such as between sedentary behavior and obesity).
Recent journal articles have noted that that the upward trend of obesity mirrors the increasingly severe trend of sleeplessness, especially among working class, where “49% of shift workers stated that, while working, they slept 6.5 hours or less… compared to estimates that the average American slept about 9 hours per night a century ago” (Vorona et al., 2005, p.25). This casually noticed, parallel trend has led to more rigorous investigation of the relationship between the two variables in the recent past, and several studies are still being processed. Only in 2004 did the Journal of the American Medical Association (JAMA) acknowledge the parallel trend between self-reported hours of sleep and obesity as a potential area of study, noting that “sleep deprivation and sleep disorders are comorbid or causative factors of diabetes and obesity” (Lamberg, 2004, p.2517).
What does this mean for the "average" person? If you are concerned about your weight and you have an irregular or short sleep schedule, it is entirely possible that your activities directed toward weight loss should include regulating your sleep schedule and ensuring that it lasts about nine hours.