Emerging data indicates that the relationship between chronic conditions and sleep disorders are likely mediated by the relationship between sleep disorders and obesity 
Lopez-Garcia E, Faubel R, Leon-Munoz L, Zuluaga MC, Banegas JR, Rodriguez-Artalejo F. Sleep duration, general and abdominal obesity, and weight change among the older adult population of Spain. Am J Clin Nutr. 2008;87:310–316. 7. Patel SR, Blackwell T, Redline S, et al. The association between sleep duration and obesity in older adults. Int J Obes (Lond). 2008;32: 1825–1834..
For example, in a study , \citep{Taheri2004} showed that shorter sleep durations were associated with 15% lower lepin levels and 14.9% higher ghrelin levels which were independent of Body Mass Index (BMI). They conclude that chronically shortened sleep duration could increase appetite leading to overeating and eventually obesity. The neuro-cognitive theory of insomnia suggests that insomnia is associated with increased levels of cortisol \citep{Perlis1997}\citet{Dallman2003}, proposed that chronic evaluation of gluocorticoids, such as cortisol may be implicated in overconsumption of high fat and sugar foods and to store fat around the abdominal area. They argue that chronically elevated levels of glucocortical hormones increase  corticotropin-releasing factor activity in the central nucleus of the amygdala which increased stimulus salience and abdominal obesity. This mechanism then moderates metabolic inhibitory feedback on the catecholamines in the brain and the expression of corticotropin-releasing factor. Accordingly, the authors propose that, in an attempt to dampen activity in the brain,  the same mechanisms which mediates hyperactivity in insomnia facilitates overconsumption of high fat and sugary foods as well as promoting abdominal obesity.