Seeing what an excess of vitamin C did to my sensitive under-eye skin skin got me thinking about what can happen when you unwittingly ingest too much of a good thing. As children, we are taught to eat our veggies...and to take our vitamins when the doctor deems our diets deficient. I bet you've never considered the possibility of vitamin overdose, but toxic symptoms can occur when the body stores vitamin levels too high to handle. The medical name for this condition is hypervitaminosis. No, that is not a fake disease some sneaky kid made up to get out of swallowing vitamins. Almost anything can become poisonous if consumed in excess, including alcohol, salt, oxygen, and - yes - vitamins.

Vitamin poisoning is a very real risk, and not only for nutrition overachievers. According to WebMD, 44% of Americans take vitamins and dietary supplements every day, and 84% of them consider these pills entirely safe. Why shouldn't they, considering 79% of doctors recommend supplements to their patients? This blind acceptance of vitamins as a beneficial regimen for everyday health makes them especially prone to consuming in excess. In 2007, 58,622 exposures to different types of vitamins were reported to poison control centers across the U.S., accounting for 17 major adverse outcomes and 1 death. Of this total, over 90% of cases occurred in children younger than 20 years old.

Which vitamins might make an individual vulnerable to OD? Fat-soluble vitamins are most likely to build up over time in the body since they are stored in the liver and fatty tissues. Typically, the side effects that rise from a high dosage of a particular vitamin disappear once the dosage is reduced. Hypervitaminosis generally happens from overdoing supplements rather than eating too much of a nutrient from dietary sources, although highly fortified foods are an exception. Even an elevated intake of multivitamins, especially those containing iron supplements, can trigger toxic side effects. A lesson in moderation:
Vitamin A: Though it accounts for only around 1% of cases reported to poison control centers, vitamin A comes with a notorious history of overdose -- probably due to its distinctive signs. When hypervitaminosis A sets in, the skin turns a yellowish-orangey hue, not unlike jaundice. More serious symptoms include bone loss, blurred vision, hair loss, and damage to internal organs (especially the liver). Overdose of vitamin A can also lead to birth defects in pregnant women. The recommended daily vitamin A intake is around 300 micrograms (mcg) for children and anywhere from 700mcg to 1,200mcg in adults. Overdosing would generally require at least doubling these amounts. Vitamin A is considered acutely toxic at doses of 25,000 IU/kg or higher.

Vitamin B-3: Also known as niacin, vitamin B-3 can be found in food sources as varied as green vegetables, animal proteins, and pumpernickel bagels. It can also be synthesized from tryptophan, which is present in meat, dairy, and eggs. The recommended daily allowance (RDA) is 20mg (9mg for young children) with a maximum of 35mg. Toxic doses are reached at 1,000 mg per day. Overdoing it on vitamin B-3 can result in dermatological flare-ups, such as skin flushing or itching, and gastrointestinal problems, such as indigestion and liver toxicity. These side-effects can be ameliorated by using sustained-release forms of niacin or supplementing dosage with aspirin. Even though doctors often prescribe around 2,000 mg of niacin to help lower cholesterol, such high doses of niacin are also known to exacerbate diabetes and gout.

Vitamin B-6: Naturally present in poultry, fish, grains, and legumes, this water-soluble B vitamin functions in protein and amino acid metabolism. Pyridoxine, a form of vitamin B-6, is the supplement of choice for bodybuilders. It is also frequently used in the treatment of PMS, ADHD, childhood autism, schizophrenia, and carpal tunnel syndrome. An excess of vitamin B-6 can lead to sensory impairment, clumsiness, and even paralysis. The RDA for adults is about 1.3 mg/day for adults and 0.5 mg/day for young children. To reach a neurotoxic limit, you would have to take chronic dosage in the range of 300 to 500 mg per day.

Vitamin D: D stands for dairy, as well as egg yolks, beef liver, fatty fish, and fortified foods. A glass of fortified milk provides around 100 IU per cup, which is about half the adequate intake for children and adults under 50. Those over 50 need at least 400 IU, and that number jumps up to 600 IU for those over 70. In addition to getting vitamin D from edible sources, your body produces this fat-soluble vitamin when exposed to direct sunlight. There is a wide variance in potential toxicity levels - ranging from 400 IU per day in children to 50,000 IU per day in adults, at which point the sunshine vitamin can cause a buildup of calcium deposits, interfering with the functioning of muscles such as heart tissue. Other characteristics of hypercalcemia include apathy, irritability, and bone pain.

Vitamin C: Even water-soluble vitamins (B-group vitamins and vitamin C), which mostly get flushed out in the urine, can wreak havoc. Just as your skin might rebel against an overly potent concentration of vitamin C, it is also possible to overdose on vitamin C supplements. Exceeding the 60-75 mg recommended daily dosage usually won't cause any significant health problems, apart from a noticeable laxative effect. However, regularly doing so - especially if combined with iron supplements - can do serious damage. A University of Florida study discovered that patients with a muscle sprain, bruise, or inflammatory disease (as well as those taking iron supplements) accumulated rust deposits inside their bodies when they consumed more than 100 mg a day of vitamin C. Symptoms of vitamin C overdose range from nausea, mouth ulcers, and malodorous urine to kidney stones, copper deficiencies, and premature death.

Non-specific symptoms like nausea, diarrhea, and rashes are common with any chronic vitamin overdose and may be more attributable to additives (such as mannitol) rather than the vitamin content. Should you suspect that you might be overdoing your daily intake of a particular vitamin or mineral, cut your dosage in half rather than quitting cold turkey. Of course, your best course of action if you're concerned (especially if you have an illness such as diabetes or high blood pressure) is to consult with a doctor or dietitian. As long as you are aware of the guidelines for the supplements you are taking (on your bottle's label), your body can reap the benefits of vitamins without going overboard.