Influence of Day Length and Physical Activity on Sleep Patterns in Older Icelandic Men and Women..

Brychta RJ, Arnardottir NY, Johannsson E, Wright EC, Eiriksdottir G, Gudnason V, Marinac CR, Davis M, Koster A, Caserotti P, Sveinsson T, Harris T, Chen KY. J Clin Sleep Med. 2016 Feb;12(2):203-13. PMID:26414978