Vitamin D belongs to a group of vitamins called fat-soluble vitamins. When you eat foods or take supplements that contain fat-soluble vitamins, your body uses what it needs and then stores the rest in your fat cells. When your dietary intake falls short, your body uses the stored vitamins to meet your needs. Because of this ability to store excess vitamin D, consuming high amounts of a vitamin D supplement regularly can make you sick.
Action of Vitamin D
Vitamin D acts as a hormone in your body and is responsible for regulating calcium and phosphorus levels. Vitamin D stimulates the absorption of these minerals in your digestive tract so that they can reach your bloodstream. Normally, this process ensures that the calcium and phosphorus levels in your blood are adequate enough keep your bones healthy. If you consume high amounts of vitamin D supplements, it can cause a toxic condition called hypervitaminosis D. Hypervitaminosis D causes a severe increase in calcium absorption and calcium loss from the bones. As a result, calcium levels in your blood accumulate to potentially dangerous levels, a condition called hypercalcemia.
Hypercalcemia
Specific symptoms of hypercalcemia can vary between individuals. The most commonly seen symptoms include nausea, vomiting, increased thirst, abdominal pain, muscle weakness, loss of appetite, frequent urination, muscle aches, joint pain, confusion, constipation and fatigue. If left untreated, hypercalcemia can lead to osteoporosis, a condition in which the bones become weak and brittle and have an increased susceptibility to breakage. If the calcium in your blood travels to your kidneys, it can cause kidney stones and eventually lead to kidney damage. Severe hypercalcemia can disrupt your heart rhythm and cause nervous system dysfunction.
Treatment
If you develop any of the symptoms of hypercalcemia, the first thing you should do is discontinue use of your vitamin D supplements. If hypercalcemia is severe, you may need hospitalization. During hospitalization, you will be given intravenous fluids and diuretics to help flush the calcium out of your blood and keep you hydrated. You may also receive hormones or medications to reverse the effects of too much vitamin D.
Upper Tolerable Intake Level
To prevent hypervitaminosis D and hypercalcemia, it is important to avoid consuming vitamin D supplements with a high concentration of the vitamin. The Food and Nutrition Board developed an upper tolerable intake level, or UL, for vitamin D. This level represents the highest amount of vitamin D that can be consumed each day without causing any adverse health effects. The UL for vitamin D for adults is 100mcg per day. When choosing a supplement, the amount of vitamin D should not exceed this amount.
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