Fat-soluble vitamins dissolve in fat and are stored in your body's tissues. These types of vitamins have a danger of toxicity because your body holds onto them until it uses them up. Water-soluble vitamins, as the name suggests, dissolve in water and are not stored in your body. Because you flush the excess from your body, it is very difficult to overdose and reach toxic levels with water-soluble vitamins, but it is not impossible.
Water-soluble Vitamins
Vitamin C and the B group are all water-soluble. There are a total of eight B vitamins: B-1 or thiamine, B-2 or riboflavin, B-3 or niacin, B-5 or pantothenic acid, B-6, B-7 or biotin, B-12, and folate or folic acid. Vitamin C contributes to collagen synthesis and tissue repair and supports the immune system. The B group helps you convert food into energy and helps form red blood cells. You can get vitamin C from fruits and vegetables and B vitamins from meats, dairy, legumes and fortified grain products.
Potential for Overdose
Vitamin C and three of the B vitamins -- B6, folate and niacin -- all have the potential for overdose through supplementation. The overdose usually occurs when you take supplements beyond the tolerable upper intake levels outlined by the National Institutes of Health. At these levels, the body is unable to clear the excess vitamin from the blood fast enough. The tolerable upper intake level varies by vitamin and by age group. In general, the tolerable upper intake level of vitamin C is 2,000 mg for adults, 1,200 to 1,800 mg for children ages 9 through 18, and 400 to 650 mg for children under age 9. The UL for niacin is 30 mg for children ages 14 to 18, and 35 mg for adults over 19. The UL for folate is 800 mcg for children 14 to 18, and 1,000 mg for adults. The UL for B-6 is 80 mg for children 14 to 18, and 100 mg for adults.
Toxicity Symptoms
The symptoms of overdose and toxicity vary by vitamin. Vitamin C causes nausea, diarrhea and abdominal cramps at high doses. Prolonged use may also cause kidney stones. A folate overdose does not have any outward symptoms, but it will mask the symptoms of a B-12 deficiency in patients with pernicious anemia. A vitamin B-6 overdose causes sensitivity to sunlight and numbness in the extremities, or neuropathy. The neuropathy may cause trouble walking, or ataxia. Niacin toxicity causes flushing, or hot flashes, nausea, tingling in the extremities and dizziness. Prolonged use can cause liver damage and increased urination, and it can alter your cholesterol levels.
Considerations
It is possible to overdose on high doses of certain water-soluble vitamins. To prevent this, avoid taking more than the recommended dose of any vitamin supplement and consult your physician before starting a vitamin and supplement program.
References
- Colorado State University Extension; Water-Soluble Vitamins; J. Anderson and L. Young; August 2008
- CSU Extension; Fat-Soluble Vitamins; Anderson and Young; August 2008
- MIT DAPER: Optimizing Your Diet: Best Foods for Specific Vitamins
- National Institutes of Health: Tolerable Upper Intake Levels
- USDA: Vitamin Toxicity Chart
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