Notably, however, one study suggests that not only is fewer than five hours of sleep associated with increased cardiovascular disease, but so is getting too much sleep! That is, people who reported sleeping for more than eight or nine hours per night also had an increased risk of coronary artery disease, stroke or death from cardiovascular causes.
If this latter study is correct, then there is an "optimal sleep range" of roughly between six and eight hours of sleep per night.
There are several theories as to why chronic sleep deprivation may predispose a person to heart disease. Chief among these is that a lack of sleep interferes with certain hormone levels - in particular, leptin and ghrelin - which affect appetite levels and energy expenditure. So, short sleep duration can increase your chances of becoming overweight, sedentary, and developing insulin resistance and metabolic syndrome.
Why too much sleep might be associated with the development of heart disease is completely unknown. It might be that people who have certain medical conditions that predispose to heart disease (such as chronic depression) might also simply sleep more hours.
Your best bet is to try to get a solid six or seven hours of sleep most nights. However, occasionally staying up late (or occasionally sleeping in!) is not particularly hazardous to your health, and in any case is a natural feature of the human condition.
Knutson, KL, Van Cauter, E, Rathouz, PJ, et al. Association between sleep and blood pressure in midlife: the CARDIA sleep study. Arch Intern Med 2009; 169:1055.
King, CR, Knutson, KL, Rathouz, PJ, et al. Short sleep duration and incident coronary artery calcification. JAMA 2008; 300:2859.
Sabanayagam, C, Shankar, A. Sleep duration and cardiovascular disease: results from the National Health Interview Survey. Sleep 2010; 33:1037.
Cappuccio FP, Cooper D, D'Elia L, et al. Sleep duration predicts cardiovascular outcomes: A systematic review and meta-analysis of prospective studies. Eur Heart J 2011: DOI:10.1093/eurheartj/ehr007.