Longer Napping Means Higher Risk
In this 2014 study, researchers followed more than 16,000 Britons for more than 13 years. They correlated the number of deaths with the napping habits of individuals and found that napping was correlated with a significantly higher risk of all-cause mortality.
Researchers found that people who napped for less than an hour a day were 14% more likely to die, while those who napped for one hour or longer were 32% more likely to die. This overall mortality correlation was independent of age, sex, social class, education level, marital status, employment status, body mass index, physical activity level, smoking status, alcohol intake, time spent in bed at night, and other confounders.
When looking at deaths due to respiratory illness for people under age 65, the correlation was even higher. People who napped for less than an hour a day were 40% more likely to die of respiratory illness, while those who napped for more than an hour a day were 156% more likely to die of a respiratory illness.