Women who slept five hours or less a night had a 65 percent greater risk of rapid decline in kidney function, compared with women sleeping seven to eight hours a night, the investigators discovered, HealthDay said. "This is concerning because as a general population the amount of sleep we are getting has decreased over the last 20 years," said lead researcher Dr. Ciaran McMullan, an instructor in medicine. It's not known whether sleeping longer improves kidney function or reverses damage caused by shortened sleep, he said. McMullan cautioned that this study can only show that decreased kidney function is associated with less sleep, not that less sleep causes the decline in kidney function. For that, more research is needed, he said. A connection between disrupted sleep and heart disease has been studied before. A link between reduced sleep and diminished kidney function might be the result of medical conditions that affect kidney function, such as diabetes and high blood pressure, McMullan said. "Diabetes occurs more often in people who sleep less, as does high blood pressure," he said. "We know that two of the greatest factors that decrease kidney function are diabetes and high blood pressure." The body's natural rhythms, or so-called circadian clock, might also play a role, McMullan said. The kidney is timed to work differently during the night than during the day because the demands on the body are different, he explained. "Maybe short sleep changes the physiology of the kidney over the daily cycle, and these changes might damage the kidney," McMullan suggested. As the US population ages and as more people suffer from diabetes and high blood pressure, the number of people with kidney disease will increase, and too little sleep may play a part, he added. "We are a sleep-deprived society," McMullan said. "The concern is that sleep deprivation will lead to a decline in kidney function." He said it's likely the findings would also apply to men, but noted that would need to be studied.