Taking too much of anything -- even when it's as healthy as vitamins -- can cause problems. Although some vitamins are relatively harmless in unlimited quantities because your body excretes the excess, others can only be taken in limited amounts before you risk harming your health.
Water-Soluble Vs. Fat-Soluble
Vitamins come in two forms: water-soluble and fat-soluble. The water-soluble vitamins are vitamin C and the B-complex vitamins. If you take in more than your body can use of these, they end up passing through you as expensive urine. Vitamins A, D, E and K, on the other hand, require fat to dissolve. Your body stores these vitamins, and if you take too much, the amount in your body can build to a harmful level.
Tolerable Upper Intake Levels
The highest amount of a vitamin you can safely take per day is known as the tolerable upper intake level, or UL. This amount is the level that's not likely to pose a risk to healthy individuals. The UL for vitamin A for adults is 3,000 micrograms, while it's set at 100 micrograms for vitamin D, says the Institute of Medicine. The UL for vitamin E is 1,000 milligrams a day. There's no UL for vitamin K, but the institute recommends caution when taking any amount over the recommended dietary allowance of 90 micrograms a day for women and 120 micrograms a day for a man. Some water-soluble vitamins have ULs, too; although they are less likely to cause harm in high amounts, there's still a risk. You can also overdose on multivitamins.
The effects of taking too many vitamins depends on which vitamins you take. For example, the adverse effects of taking too much vitamin A include liver abnormalities, nervous system changes, vertigo and muscular incoordination. The biggest risks of too much vitamin D include hypercalcemia -- a high level of calcium in your blood -- as well as nausea and renal disorders. Although toxicity of vitamin C is low, Colorado State University Extension says there is a risk of kidney stones, gout, diarrhea and rebound scurvy if you consume it in excess. Taking too much folate, or vitamin B-9, can mask a vitamin B-12 deficiency. Overdosing on a multivitamin comes with a host of health effects, including frequent urination, eye irritation, irregular or rapid heartbeat, bone or joint pain, confusion, seizures, fainting, itching or rash, hair loss, nausea or diarrhea.
If you overdose on a multivitamin, seek immediate medical attention by contacting either a health care professional or the National Poison Control Center. If you experience symptoms from single-vitamin overdoses, contact your doctor immediately for treatment.