An overdose of vitamin D is called hypervitaminosis D, or vitamin D toxicity. The effects of vitamin D overdose include gastrointestinal disturbances, increased blood pressure and increased levels of calcium in the blood (hypercalcemia), which can lead to irregular heartbeat and other medical problems. It is unlikely that an overdose of vitamin D would result from diet or from the body’s own ability to synthesize this nutrient; overuse of supplements or supplemental fish oils is more likely to be the cause. The safe upper limit for vitamin D intake, established by the Food and Nutrition Board of the Institute of Medicine, is set at 2,000 international units (IU) a day. Speak to your doctor about the best dosage if you plan to take vitamin D supplements for any reason.
Nausea, vomiting, constipation and loss of appetite are all symptoms of vitamin D overdose that can affect the stomach and intestinal tract. While these are not the most serious side effects of vitamin D toxicity, gastrointestinal problems may be early indicators of hypercalcemia, which can lead to additional health problems.
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A vitamin D overdose can result in hypercalcemia because one of the roles vitamin D plays in the body is controlling the levels of calcium in the blood. Hypercalcemia is a serious condition if it becomes chronic, and can lead to bone mineral loss, or decalcification of the bones that leaves them brittle and weakened. At the same time, ongoing hypercalcemia can result in abnormal and debilitating calcium deposits in the kidneys and other organs. Signs of chronic hypercalcemia include excess thirst, fatigue, headaches, dry mouth, insomnia, mood changes, ringing in the ears, dizziness and vertigo.
Vitamin D overdose may also result in hyperphosphatemia, or too much phosphorus in the blood. Along with elevated blood calcium levels, high phosphorus levels can lead to hardening of the arteries, cardiovascular disease and death from heart attack, particularly in anyone with a kidney condition.
The effects of vitamin D overdose can linger for months, even after supplements are stopped. High blood pressure, possibly with fever and more severe gastrointestinal problems, may be experienced as a later symptom of vitamin D overdose. High blood pressure does not produce early symptoms but ultimately contributes to atherosclerosis, kidney failure, heart attack and stroke if left untreated.
Rare but possible effects of vitamin D overdose include blindness, deafness, seizures, elevated cholesterol and even death, according to University of Michigan Health System professionals. People with certain medical conditions, such as hyperparathyroidism and a variety of inflammatory diseases, are particularly sensitive to vitamin D and are more susceptible than healthy people to the extreme effects of vitamin D overdose.