According to WebMD, some research has linked vitamin D deficiency to chronic fatigue syndrome. It is said that a vitamin D deficiency has the ability to disrupt your sleep cycle and worsen other disorders that may cause fatigue. “According to a study in the August 2013 issue of "Endocrine." If you have a vitamin D deficiency affecting your ability to get to sleep or stay asleep throughout the night, you're more likely to feel tired throughout the day (SFGATE).”