Toxicity & Vitamins

Vitamins are classified into two categories: water-soluble and fat-soluble. The water-soluble vitamins, including the B vitamins and vitamin C, are not stored in the body, so excess amounts are simply eliminated in the urine. Conversely, fat-soluble vitamins -- vitamins A, D, E and K -- are stored in fat tissue and various organs and are not quickly eliminated, so accumulation to toxic levels can occur with long-term consumption of large doses.

Vitamin A

Vitamin A toxicity, or hypervitaminosis A, usually results from taking excess amounts of this vitamin in supplements. Acute toxicity, which develops after taking large amounts over a short period of time, may manifest with symptoms of nausea, vomiting, dizziness, headache and blurred vision. The tolerable upper intake level for vitamin A is 10,000 IU; the risk of adverse health effects like birth defects, liver problems, reduced bone mineral density and nervous system disorders increases at intakes greater than this level.

Vitamin D

Synthesis of active vitamin D is tightly regulated, so toxicity only results when excessive doses are taken. Adults who take 50,000 IU per day for several months develop vitamin D toxicity, according to Merck Manuals. Symptoms are due to hypercalcemia, or too much calcium in the blood, and they include nausea, vomiting and loss of appetite, which can be followed by frequent urination, extreme thirst, weakness, itchy skin and eventually kidney failure. Treatment entails stopping vitamin D intake, IV hydration with corticosteriods or bisphosphonates to reduce blood calcium levels, and reducing calcium intake.

Vitamin E

Vitamin E acts as an important antioxidant in the body, preventing damage to cells. Many adults take large amounts of vitamin E for long periods of time without apparent harm, but occasionally fatigue, nausea, diarrhea and muscle weakness can occur. There are also some reports of bleeding, hemorrhagic stroke and premature death with high vitamin E intake.

Vitamin K

There is no known toxicity associated with phylloquinone or menaquinone, simply referred to as vitamins K1 and K2. However, the synthetic form called menadione, or vitamin K3, can be toxic. It interferes with certain antioxidants, causing oxidative damage to cell membranes. It can induce jaundice, the rupture of red blood cells and liver toxicity in infants.

Vitamin C

This vitamin is water-soluble, so any excess vitamin C is simply excreted through the urine. As a result, toxicity is rare. However, amounts greater than 2,000 mg per day can lead to intestinal problems like diarrhea and stomach pain.

The B Vitamins

The B vitamins are all water-soluble, toxicities rarely develop. However, occasionally excessive amounts of vitamin B-1 cause headaches, convulsions and cardiac arrhythmia. Larges doses of vitamin B-3 are used to treat high blood cholesterol, but some side effects include intestinal problems, liver injury, headaches, a rise in uric acid levels potentially leading to gout and elevated glucose levels. Similarly, large doses of vitamin B6 are given to prevent or treat certain issues, but some symptoms of neuropathy may develop.