In general, only the fat-soluble vitamins A, D, E and K have the potential to be toxic and only when taken as supplements in high doses over time. Vitamins C and B-complex are water-soluble and, as such, are eliminated from your body much more quickly than the fat-soluble vitamins, which are stored in fat cells for longer periods of time. The Food and Nutrition Board of the National Academy of Sciences Research Council has established Tolerable Upper Intake Levels (UL) for most of the fat-soluble vitamins. Beyond these UL doses, symptoms of toxicity may appear.
Vitamin A
For teenagers and adults age 14 and over, the Daily Reference Intake (DRI), or safe intake level, of vitamin A for females is 2,333 international units (IU) or 700 micrograms (mcg). For the same age males, the DRI is 3,000 IU or 900 mcg. The UL for both males and females is 2,800 mcg for ages 14 to 18 and 3,000 mg for ages 19 and above. Symptoms of mild vitamin A toxicity include nausea, irritability and blurred vision. Symptoms of more severe toxicity include hair loss, bone pain, skull pressure, skin changes and enlarged liver and spleen.
Vitamin D
The DRI for vitamin D for males and females ages 14 to 50 is 5 mcg or 200 IU. For ages 51 to 70, the DRI is 10 mcg or 400 IU. For ages 71 and above, the DRI is 15 mcg or 600 IU. The UL for vitamin D for all males and females over the age of 14 is 50 mcg. Symptoms of vitamin D toxicity include excessive absorption of calcium, which results in too much calcium in your blood. This can interfere with normal hormone and nerve functions. Other possible effects of vitamin D toxicity include kidney damage, decreased appetite, nausea and vomiting.
Vitamin E
The DRI for vitamin E for both men and women ages 14 and above is 15 mg or 22.5 IU. The UL for male and females ages 14 to 18 is 600 mg and for everyone ages 19 and above, 1,000 mg. Supplemental doses of vitamin E can interfere with your body's blood clotting process and interact with blood-thinning and statin medications.
Vitamin K
A recommended daily value of 80 mcg has been established for vitamin K. The most common food sources of vitamin K, leafy green vegetables such as spinach, kale, collard greens and mustard greens, contain three to eight times the daily value in a single 1/2-cup serving. Although there is no official UL for vitamin K, it is known that higher doses can cause liver damage and disintegration of red blood cells. If you are taking a blood-thinning medication, speak to your doctor about appropriate vitamin K levels.
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