The main symptoms of vitamin D overdose which are those of hypercalcemia including anorexia , nausea, and vomiting. These may be followed by polyuria , polydipsia , weakness, insomnia, nervousness, pruritus and ultimately renal failure . Furthermore, proteinuria , urinary casts , azotemia , and metastatic calcification (especially in the kidneys) may develop.  Other symptoms of vitamin D toxicity include mental retardation in young children, abnormal bone growth and formation, diarrhea, irritability, weight loss, and severe depression.  
This type of vitamins is a type of fat-soluble secosteroids. Vitamin D in addition to helping the body absorb calcium also helps the body keep the right amount of calcium and phosphorus in the blood. A Vitamin D deficiency in the body can cause rickets which is most commonly seen in children. It could also lead to a condition known as osteoporosis in adults. There is also a lot of ongoing research regarding D3 vitamin for depression as well as other D3 vitamin benefits. An excess of vitamin D is known to cause high levels of calcium in the blood resulting in calcium deposits in sensitive organs such as the heart and lungs. This is one of the main vitamin D3 side effects and is generally the result of an excessive intake of Vitamin D supplements and not through dietary choices. It is important that a person suffering from vitamin D side effects receive immediate treatment to prevent further complications. D3 vitamin deficiency reduces the amount of calcium and phosphorous that is absorbed by the body and so it is important that children and young adults receive adequate amounts of this vitamin.