You may be considering vitamin D supplements if you think you're not getting enough of this essential nutrient from food, such as fortified dairy products, or from sunshine. Medical cases involving too much vitamin D-3 are rare, but ingesting excessive amounts can cause toxic effects, according to the Vitamin D Council.
Types and Doses
Vitamin D-2, synthesized by plants, and vitamin D-3, produced by humans in skin during exposure to sunlight, are both available as supplements. You can buy high-potency vitamin D-3 supplements of 5,000 IU. Published cases involving vitamin D toxicity have all involved an intake of at least 40,000 IU per day, according to the Vitamin D Council. In two cases, men were taking over 2 million IU of vitamin D per day, and both survived. Such high doses can cause permanent physical damage, however.
Digestive Effects
Too much vitamin D-3 can cause unpleasant gastrointestinal effects. Immediate effects from an acute overdose include abdominal cramps, nausea and vomiting. Excessive vitamin D-3 taken on a long-term basis can cause these symptoms, along with constipation, which may alternate with diarrhea; tingling sensations in the mouth; lack of appetite; and weight loss.
Electrolyte Imbalance Symptoms
Additional effects from vitamin D toxicity may include confusion, nervousness, weakness, generalized itching and heart rhythm abnormalities. Vitamin D boosts calcium absorption, and these symptoms can be signs of excess calcium in the blood if you take very high doses of vitamin D. Known as hypercalcemia, excess blood calcium is an electrolyte imbalance that can become dangerous.
Hypercalcemia
Hypercalcemia can lead to deposits of calcium crystals in the heart, lungs and kidneys. Permanent damage to these organs is possible if hypercalcemia is severe and allowed to continue for a prolonged time. Calcification in the kidneys from excess blood calcium can eventually result in kidney failure, warns Merck Medical Manuals. In most cases, however, vitamin D toxicity can be resolved without permanent health problems if the condition has not gone on too long, according to the Vitamin D Council.
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