In the right doses, the cure can kill. Yet it is done as we self-medicate with the belief that we will prevent or abort occurring processes. Toxicity caused by vitamins can be acute, or it can be chronic. In the case of the former, toxicity causes increased intracranial pressure, drowsiness, irritability, abdominal pain, nausea, and vomiting. Sometimes the skin subsequently peels. Early symptoms of chronic toxicity are sparsely distributed and may include coarse hair; alopecia of the eyebrows; dry, rough skin; dry eyes; and cracked lips. Later, severe headache, pseudo-tumor cerebri, and generalized weakness develop. Cortical hyperostosis of bone and arthralgia may occur, especially in children, while fractures may occur easily in elderly.
Vitamin A Toxicity
Both acute and chronic toxicity usually cause headaches and increased intracranial pressure. Acute toxicity also causes nausea and vomiting and is seen in children who accidentally took large doses, or in children who ingest seal or bear liver. Chronic toxicity occurs from megavitamin therapy and can cause changes in skin, hair, and nails; abnormal liver test results; and in a fetus, birth defects.
Vitamin B6 Toxicity
The ingestion of mega-doses of pyroxidoxine may cause peripheral neuropathy with deficits in a stocking-glove distribution, including progressive sensory ataxia and severe impairment of positon and vibration senses. Senses of touch, temperature, and pain are less affected. Motor and central nervous system are usually intact.
Vitamin C Toxicity
The upper limit for vitamin C intake is 2000mg per day. Up to 10g per day of vitamin C are sometimes taken for unproven health benefits, such as preventing or shortening the duration of viral infections or slowing or reversing the progression of cancer or atherosclerosis. Such doses may acidify the urine, cause nausea and diarrhea, interfere with the healthy antioxidant-prooxidant balance in the body, and in patients with thalassemia or hemochromatosis, promote iron overload.
Vitamin D Toxicity
Because the synthesis of vitamin D is tightly regulated, toxicity usually occurs only if excessive doses are taken. The main symptoms results from hypercalcemia. Anorexia, nausea and vomiting can develop, often followed by polyuria, polydipsia, weakness, nervousness, pruritus, and eventual renal failure. Proteinuria, urinary casts, azotemia, and metastatic calcifications may also present.