"All things in moderation" is a common expression, and is very true, as even nutrients such as oxygen can be harmful in high amounts. While true overdose with vitamins is rare, side effects can be quite severe if it does occur. Excess amounts of water-soluble vitamins such as vitamins B and C leave the body through urine while other vitamins are fat-soluble and will build up in the system. The National Institutes of Health recommends calling Poison Control if you suspect an overdose.
RDA
All nutrients have a recommended daily allowance set by the FDA or USDA. The daily allowance is set based on the minimum the body needs to function. There are also tolerable upper intake levels, or UL, for each vitamin. The upper intake levels vary, but most allow for five to ten times the RDA levels in adults before symptoms of toxicity show up.
Vitamin A
Toxicity from too much vitamin A can happen either quickly or slowly over time, according to PubMed Health. A large number of symptoms can develop from over supplementation including skin and visions changes, drowsiness, dizziness and vomiting. In children, excess vitamin A can cause double vision, abnormal softening of the bones and bulging of the fontanelles between the cranial bones. Women who overdose while pregnant may put the unborn child at risk for birth defects. Treatment simply involves stopping supplementation of vitamin A. Most recover without incident, and it is rarely fatal unless the dose caused irreversible liver damage.
Vitamin E
Most vitamin overdoses will include nonspecific symptoms such as headache, stomach upset, diarrhea, nausea and generalized fatigue. The bigger concern with overdose of vitamin E is thinning of the blood, leading to increased risk for internal bleeding. Those taking blood thinners like cumadin, have higher risk. Treatment for this overdose will have to include treatment for any internal bleeding as well as decreasing the dose of vitamin E into a normal range.
Vitamin D
Overdose of vitamin D leads to all the vague symptoms associated with other toxicities but also leads to hypercalcemia, or too much calcium in the blood. This excess calcium can lead to an increased risk for kidney stones, according to the Mayo Clinic. The main source of vitamin D is from sun exposure, but overdosing or toxicity occurs only when supplementing.
Multivitamin Toxicity
Overdosing on more than one vitamin at a time can lead to all the similar symptoms as reported above. It is important not take more than one variety of multivitamin at one time and to take in no more than the recommend doses. It is equally key to avoid vomiting if the excessive dose was taken recently and to instead contact poison control or a medical professional.
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