Vitamins are classified as either water or fat soluble. Excessively high intakes of fat soluble vitamins can lead to toxicities because your body has the capacity to store any excess intake. Most water soluble vitamins, on the other hand, do not build up in the body to toxic levels since excesses are excreted in the urine. Vitamins C, niacin and B-6 are the exceptions to this. Tolerable upper intake levels have been established to safeguard against possible toxic intake levels.
Background
Your body has the capability to store fat soluble vitamins, A, D, E and K, in the liver and fatty tissues when intakes exceed needs. Because of this, high dosages have the potential to cause toxicities.Toxicity risks occur only from high dosage supplements, not from just eating food. More is not always better when it comes to vitamin intakes.
Vitamin A
The tolerable upper intake level for vitamin A in adults is 3,000 mcg RAE. Be sure and check the labels of any supplements you take to ensure that your dosage falls below this. Initial vitamin A toxicity signs include headaches, nausea, loss of appetite, blurry vision and dry scaly skin. Over time, hair loss, joint pain, bone fractures, impaired growth and liver damage may occur. Excessive vitamin A intake during pregnancy can also lead to birth defects.
Vitamin D
Mega dosages of vitamin D adversely affect many body organs, including the kidneys, brain, heart and bones. The nervous system can also be affected causing depression. The tolerable upper intake level for vitamin D is 50 mcg, or 2,000 IU. Signs of toxicity include nausea and vomiting, impaired growth and high blood calcium levels. Infants and the elderly are most susceptible to vitamin D toxicity from supplements. .
Vitamin E
Even though vitamin E is fat soluble, toxicity risk is not as great as with vitamins A and D. In individuals on blood thinning medications excessive vitamin E intakes can impair blood clotting ability causing uncontrolled bleeding. High dosages of vitamin E may also interfere with the proper workings of statin drugs. Individuals on these medications should not take vitamin E supplements.
Vitamin K
Although there is no established tolerable upper intake level for vitamin K, high dosages can contribute to liver damage and red blood cell breakdown resulting in jaundice.
Others
The water soluble vitamins C, niacin and B-6 also have toxicity problems associated with them. The tolerable upper intake level for vitamin C is set at 2,000 mg. Toxicity signs include nausea, cramping, diarrhea and susceptibility to gout and kidney stones. Large dosages of niacin can cause liver damage, vision problems, excessive sweating and a rash known as niacin flush. Vitamin B-6 also has the potential to be toxic at dosages above the tolerable upper intake level of 100 mg. Signs of this include memory impairment, irritability, depression, headaches and nerve damage.
References
- Institute of Medicine Dietary Reference Intakes: Recommended Dietary Allowances and Adequate Intakes for Vitamins
- Institute of Medicine: DRIs for Calcium and Vitamin D
- Linus Pauling Institute at Oregon State University: Vitamin K
- National Institutes of Health Dietary Supplement Fact Sheet: Vitamin A and Carotenoids
- eMedicine Endocrinology: Vitamin E Toxicity
- Colorado State University Extension: Fat Soluble Vitamins; J. Anderson and L. Young; August, 2008
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