Vitamin Toxicity: What Happens If You Overdose on Vitamins?

Vitamins are vital if the body is to carry out basic metabolic functions. Overdosing on vitamins may produce symptoms like bleeding, stomach pain, liver damage, and other symptoms.

Vitamins are vital if the body is to carry out basic metabolic functions. They're essential for immunity, vision, growth, and other activities. You probably get all the vitamins you need if you eat a healthy, balanced diet, but people see vitamins as safe and often take over-the-counter supplements, too. 

However, vitamin toxicity is possible if you take too high a dose of any vitamin. Vitamins are not always harmless, and some can cause severe and life-threatening adverse effects.

Vitamins are often classified as fat-soluble or water-soluble. 

The kidneys remove water-soluble vitamins if you eat too much in a day. They don't collect in your body, and toxicity only occurs if you take enormous amounts. Water-soluble vitamins include:

• Vitamin B1 (thiamine)
• Vitamin B2 (riboflavin)
• Vitamin B3 (niacin)
• Vitamin B5 (pantothenic acid)
• Vitamin B6 (pyridoxine)
• Vitamin B7 (biotin)
• Vitamin B9 (folate)
• Vitamin B12 (cobalamin)
• Vitamin C (ascorbate)

Your body can't get rid of the fat-soluble vitamins as easily. If you consume more than you need, these vitamins collect in your body and can cause vitamin toxicity over time. Four fat-soluble vitamins include:

• Vitamin A (retinol)
• Vitamin D (calciferol)
• Vitamin E (alpha-tocopherol)
• Vitamin K (phylloquinone)

Vitamin A is essential for your vision, immunity, skin, and digestive system function. This vitamin is widely available in food, so it is rare for Americans to be deficient in this vitamin unless they have a disorder like cystic fibrosis or malabsorption. This vitamin might even be stored in the liver if you consume too much.

Vitamin A toxicity can result if you take supplements over a long time. Liver and liver pâté also have high concentrations of vitamin A, so eating them even once a week might give you too much of this vitamin. If you eat liver frequently, be careful not to have any multivitamin supplements that contain vitamin A. Fish oil also contains vitamin A.

Eating more vitamin A than you need can weaken your bones. You will be at risk of osteoporosis and fractures when you're older. Vitamin A is especially dangerous during pregnancy. High consumption of the active form, retinol, can cause birth defects, including abnormalities of the skull, eyes, heart, and lungs.

Women past menopause and older men are already at risk of osteoporosis, so they should take precautions to avoid vitamin A toxicity:

• Don't eat liver and liver products more than once a week. Also, serve yourself smaller portions.
• Don't have more than 1.5 milligrams of vitamin A in supplements.
• If you eat liver once a week, don't take any vitamin supplements that contain vitamin A, including fish liver oil.

Most B vitamins are safe even if you exceed the recommended doses. However, large doses of niacin (B3) can cause skin flushing. Taking large doses for a long time even causes liver damage.

Vitamin B6 is dangerous if you take 200 milligrams a day or more (the daily requirement is 1.2 to 1.4 milligrams). An overdose can lead to numbness in your hands and legs, a condition known as peripheral neuropathy. If frequent overdoses occur over a long time, this condition could become permanent. For your safety, don't take more than 10 milligrams of vitamin B6 a day.

The other B vitamins aren't typically toxic even when taken in large quantities, but you should still only take supplements under your healthcare provider's supervision.

Vitamin C is water-soluble and doesn't collect in your body. The daily requirement of vitamin C is 40 milligrams. Toxicity is only likely if you consume enormous doses (i.e, more than 1,000 milligrams a day). 

In extreme cases, you may experience side effects like:

• Stomach pain
• Bloating
• Diarrhea

These symptoms should clear up when you stop taking excessive vitamin C, though.

Vitamin D is generated in the skin when it is exposed to the sun. However, this may not be enough. The recommended dietary allowance (RDA) is 600 International Units (15 micrograms) per day for adults. People over 70 should have 800 IU (20 micrograms) per day.

The recommended daily amount of vitamin E is 3 to 4 milligrams. If you take larger amounts, they will be stored in the body.

Supplements often contain 100 to 1,000 milligrams of vitamin E and may cause toxicity. Symptoms include excessive (sometimes internal) bleeding. Discontinuing the supplement usually stops the bleeding, but bleeding into the brain (intracranial hemorrhage) can be fatal.

The daily requirement of this vitamin is 1 microgram per kilogram of body weight, so if you weigh 60 kilograms (132 lb), you need 60 micrograms of vitamin K daily. A deficiency of vitamin K is rare today. Though this vitamin is fat-soluble and stored in your body, no dangerous toxicity symptoms have been associated with the standard form. Toxicity previously affected babies who received vitamin K3 (menadione), but that form of vitamin K is no longer used.