Since it's almost impossible to eat enough food for vitamin toxicity to occur, the likeliest way too get too much of certain vitamins is by taking excessive quantities of supplements.
What is Considered Excessive?
Currently there is no clear definition of what constitutes excessive when it comes to vitamins. However, the general consensus is that excessive is considered to be several times the RDA (Recommended Dietary Allowance) or more than the Tolerable Upper Intake Level (UL) set by the Institute of Medicine.
Which Vitamins are Toxic in Large Doses?
Vitamin A: The UL of vitamin A for adults is 3,000 mcg (10,000 IU). Anything over that and the following may occur: liver damage, reduced bone density which may result in osteoporosis, and central nervous system disorders. Also, pregnant women who take more than the UL doubles the risk of giving birth to a child with birth defects. Vitamin A taken in great amounts over a short period of time can result in: nausea, vomiting, headache, abnormal vision, constipation, loss of appetite, and low-grade fever.
Vitamin B6: Long-term use of more than 100 mg of vitamin B6 may result in damaged nerves in the arms, legs, hands, and feet. It is not clear whether this damage is reversible once supplementation has stopped.
Vitamin C: Healthy adult non-smokers who take more 1,000 mg or more of vitamin C may experience stomach upset, diarrhea or constipation.
Vitamin D: The UL of vitamin D is 50 mcg (2,000 IU) for adults. Long-term megadoses higher than the UL can result in: kidney damage, heart damage, nausea, vomiting, loss of appetite, weight loss, muscle weakness, mental confusion, and elevated levels of calcium in the blood.
Large doses of vitamin D taken over a short period of time typically does not cause toxicity as excess vitamin D is stored and used by the body as needed.
Vitamin E: Since vitamin E acts as an anticoagulant and may increase the risk of bleeding problems, the Food and Nutrition Board of the Institute of Medicine recommends the UL of vitamin E to be 1,000 mg (1,500 IU). Also, excessive levels of vitamin E may cause dizziness or an upset stomach.
To avoid vitamin toxicity, healthy adults should choose quality supplements that contain no more than the RDA for any ingredient and only take the amount listed on the label. Combining a daily multivitamin with a healthy diet can ensure that the body is getting all the vitamins and nutrients it needs without risking the health effects of vitamin toxicity.
Source:
Jennifer Murray - Jennifer Murray is a freelance writer specializing in nutrition, weight loss and fitness.
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