While some vitamin D is good for you, too much can be harmful to your health. It's quite possible to overdose on vitamin D because your body stores this fat-soluble vitamin, so toxic levels can accumulate over time if you consume too much. Vitamin D toxicity, or hypervitaminosis D, may cause potentially serious complications that endanger your good health.
How Much Is Too Much?
Vitamin D toxicity occurs almost exclusively from consuming too many nutritional supplements as opposed to excess amounts from your diet or sun exposure. The recommended upper limit for vitamin D intake is 4,000 international units or 100 micrograms daily, including both dietary and supplemental sources. If you take multivitamins and vitamin D supplements, check the dose in each to determine the total amount of supplemental vitamin D you consume daily. Also check the ingredients if you take a calcium supplement; many brands include vitamin D.
Vitamin D stimulates active absorption of dietary calcium from your small intestine. It also promotes urinary retention of calcium in your kidneys. An abnormally high amount of vitamin D in your body may cause an elevated blood calcium level, or hypercalcemia. Many of the signs and symptoms of hypervitaminosis D stem from too much calcium in your body.
Nausea, Vomiting and Loss of Appetite
Early symptoms of too much vitamin D include appetite loss, nausea and vomiting. Constipation may also occur. Because many medical conditions cause these symptoms, you may not immediately associate them with excess vitamin D intake.
The calcium concentration in your muscle cells and bloodstream influences muscle function. With a high blood calcium level due to vitamin D toxicity, you may experience muscle weakness and easy fatigability. Muscle tics and twitching may also occur.
Increased Urination and Thirst
Excess calcium in your bloodstream caused by hypervitaminosis D commonly leads to increased urination. Because you lose total body water through excess urination, your thirst also increases. If your water intake does not keep pace with the losses through your kidneys, you may become dehydrated.
Hypercalcemia associated with vitamin D toxicity may cause problems with your kidneys, potentially leading to kidney failure. Formation of calcium-containing kidney stones may occur and contribute to reduced kidney function. Loss of protein through your urine is a common sign of kidney damage.
Irritability and Fatigue
The chemical imbalances in your body that occur with hypervitaminosis D can affect your mental state, commonly causing irritability, nervousness and fatigue. Although these symptoms occur with many illnesses, their presence along with others associated with hypervitaminosis D can help your doctor determine the correct diagnosis.