However, some research suggests that napping could have a dark side. Long daytime naps are associated with increased risk of death, particularly from respiratory illness, according to a longitudinal study in the United Kingdom that controlled for factors like age, weight, and income. But this study, which spooked many a reader in 2014, showed a correlation, not a causation. While more research still needs to be done, experts say that instead of naps causing disease, it's possible that people who are developing respiratory conditions simply take more naps. Similar studies have found correlations with other health issues. For example, elderly Japanese people were more likely to nap regularly if they smoked or struggled with insomnia, among other problematic health factors. Napping didn't cause these problems, per se, but it didn't appear to fix them either.