A study presented at a scientific congress Thursday reported a link between long naps and a higher risk of diabetes, though it couldn’t say if daytime sleeping was a symptom or a cause. People who slept more than an hour each day were 45 percent more likely to develop type 2 diabetes, a debilitating condition associated with overweight and a sedentary lifestyle, the study found. Without treatment, the disease can lead to blindness, nerve damage, kidney failure, heart disease and premature death.