With a long list of to-dos and not enough hours in the day, you might be tempted to skimp on the amount of z's you get. Besides, you can sleep when you're dead, right? But, if you sleep less than six or seven hours a night, death might come sooner than you think. Over the past few years, an abundance of research has come to light linking sleep deprivation to everything from obesity to cancer. Many unknowns remain; in fact, scientists aren't even completely sure as to why we sleep, and last year, researchers from Britain's University of Warwick Medical School found that getting too much sleep can be equally unhealthy for reasons they have yet to pin down. While the scientific community wrestles over the finer facts of slumber, they have begun to determine the causal relationships between lack of sleep and the following ailments:

Obesity. A Columbia University study involving nearly 10,000 people found a correlation between lack of sleep and a higher body mass index (BMI). Those who got only two to four hours of sleep every night were 73 percent more likely to have an elevated BMI; those getting five or six hours were more prone to obesity by 50 percent and 23 percent, respectively. Researchers believe that sleep deprivation triggers an imbalance in the levels of the hormones ghrelin and leptin, raising the former (which increases the appetite) while lowering the latter (which induces feelings of satiety).

Diabetes. Not getting enough deep sleep can make your body less sensitive to insulin and decrease its ability to regulate blood sugar levels, which can lead to the onset of type 2 diabetes, according to researchers at the University of Chicago. The study found that when the slow-wave sleep patterns of young, healthy subjects was disturbed, the participants were 25 percent less sensitive to insulin and experienced a 23 percent increase in blood sugar levels. 

Heart Disease. Participants in Harvard University's Nurses Health Study who slept for just five or six hours a night were shown to be at a significantly greater risk for a coronary event. Lack of sleep has been associated with high blood pressure and elevated levels of stress hormones such as cortisol. Additionally, a study conducted at Pennsylvania State University found that people who didn't get sufficient sleep had higher levels of cytokine in their blood, triggering inflammation, which damages tissue and plays a significant role in heart disease.

Cancer. Lack of quality slumber can also cause an imbalance in hormonal levels. Melatonin, a hormone that the brain produces while you sleep, plays an important role in wiping out free radicals, so any factor that diminishes its production also diminishes the body's cancer-fighting capabilities.

Accidents. Researchers at the University of Pennsylvania reported that study participants who got only four to six hours of sleep a night over a two-week period exhibited significant cognitive deficiencies on par with those who hadn't slept for three days in a row. Worst of all, they were unaware of how sleep deprived they were or how much it was affecting their ability to function. Such cognitive dysfunction can lead to accidents in the workplace, at home, and on the road. The National Sleep Foundation estimates that 100,000 highway crashes are caused by fatigue.