One that declares itself atheist. After all, one uses countries that officially declare themselves to be religious as officially religious, does one not?
Sources? All officially atheist societies. :shrug:
But if you want specific studies (which are rare in officially atheist societies, since they also happen to be low on freedom as well as anti-intellectual)
The empirical literature from epidemiological and clinical studies regarding the relationship between religious factors (eg, frequency of religious attendance, private religious involvement, and relying on one's religious beliefs as a source of strength and coping) and physical and mental health status in the areas of prevention, coping, and recovery was reviewed. Empirical studies from the published literature that contained at least 1 measure of subjects' religious commitment and at least 1 measure of their physical or mental health status were used. In particular, studies that examined the role of religious commitment or religious involvement in the prevention of illness, coping with illnesses that have already arisen, and recovery from illness were highlighted. A large proportion of published empirical data suggest that religious commitment may play a beneficial role in preventing mental and physical illness, improving how people cope with mental and physical illness, and facilitating recovery from illness. However, much still remains to be investigated with improved studies that are specially designed to investigate the connection between religious involvement and health status. Nevertheless, the available data suggest that practitioners who make several small changes in how patients' religious commitments are broached in clinical practice may enhance health care outcomes.
http://archfami.ama-assn.org/cgi/content/full/7/2/118
