Vitamin D3 is a fat-soluble Vitamin. Only a handful of foods contain significant amounts of this Vitamin, such as cod liver oil, salmon and eggs, and although our body can produce it from sunlight, Vitamin D deficiency is very common. This is associated with poor sleep quality, increased stress, cardiovascular disease and growth disruption. Supplementation has been shown to decrease fatigue and improve sleep. Of the two main forms of vitamin D, i.e., D2 and D3, the latter is more effective at raising vitamin D levels in the blood.