Recent scientific evidence has indicated that the daily physiologic requirement of vitamin D may be as high as 4,000 international units per day. The peripheral and central nervous systems, along with T-cells have sites of vitamin D action. It is likely that vitamin D modulates serotonin and melatonin synthesis and metabolism. In testing my patients I find it takes 2 to 3 drops directly under the tongue each day to get to the upper levels of normal. 2000 IU per drop. 1 fluid ounce.
Sublingual is the method of choice for raising levels of Vitamin D3 in obese or moderately overweight individuals.