Vitamin D comes in two forms and and plays a critical role in controlling calcium levels and regulating cell health and the immune system. Your body can make vitamin D from sunlight, and some foods also contain it. You can also take capsules containing the two forms of the vitamin: vitamin D2, or ergocalciferol, and vitamin D3, or cholecalciferol. If you buy a vitamin D supplement over the counter, it's vitamin D3.
Upper Intake Limits
Vitamin D is a fat-soluble vitamin, meaning you body stores what it does not immediately need. You cannot get too much vitamin D from the sun, but if you take over-the-counter vitamin D3 capsules you should know how much of the nutrient your body can safely accommodate. The upper intake limits for vitamin D3 depend on your age. For children and adults 9 and older, the maximum daily intake is 4,000 IUs per day, or 100 mcg. For kids between the ages of 4 and 8, the maximum daily intake is 3,000 IUs or 75 mcg. Toddlers who are 1 to 3 years old should get no more than 2,500 IUs or 63 mcg per day. For babies younger than 6 months, the established maximum intake is 1,000 IUs or 25 mcg. For babies between 7 and 12 months old, the maximum daily intake is 1,500 IUs or 38 mcg.
People who take over-the-counter vitamin D3 supplements may experience excessive thirst, frequent urination, constipation, diarrhea, vomiting, poor appetite, weight loss, a metallic taste, bone pain, muscle problems, fatigue, itchy skin and sore eyes, the University of Maryland Medical Center reports. Side effects more commonly occur with high doses of cholecalciferol. Before taking vitamin D3 capsules, consult with your doctor about a safe and effective dose.
Vitamin D Toxicity
If you take high doses of vitamin D3 over an extended period, you may end up with too much of the vitamin stored in your body. This can cause potentially serious health effects. In particular, too much vitamin D can cause the level of calcium in your blood to increase, a condition called hypercalcemia. People who have hypercalcemia can experience loss of bone mass and may also develop kidney stones and calcium deposits in other organs. This high blood calcium level has been associated with massive doses of vitamin D3 in excess of 50,000 IUs per day.
Because vitamin D3 capsules can affect calcium levels in the body, people with certain conditions should not take them. If you already have a high calcium level because of another health condition, do not take vitamin D3 your doctor advises you to do so. The vitamin also may not be safe for people who have high phosphorus levels and those with heart and kidney disease, the University of Maryland Medical Center reports.