A recent 2015 study of older men also found that lower vitamin D levels were associated with shorter sleep duration and more time spent awake after initially falling asleep. (sonima.com)
There is however little existing data showing the effects of chronic short sleep duration under natural conditions. (ahealthblog.com)
This study used «real world» conditions which showed that shorter sleep duration shuts down processes involved in the immune response of circulating white blood cells. (ahealthblog.com)