Can You Really Overdose on Vitamins?

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​Vitamins are essential for your health, but you only need them in small amounts and you should be able to get plenty from the foods you eat. But can you get too much of any one vitamin?

Yes, absolutely. While it's nearly impossible to get too much of any vitamin from eating foods, you can overdose on some vitamins if you take large doses of supplements for extended periods of time.

How Can That Happen? I Thought Supplements Were Safe

Most of the vitamin supplements you see on store shelves are sold in dosages that won't cause problems as long as you follow the label directions.

 But sometimes people take much larger amounts, called "mega-doses" of vitamins, hoping the supplements will help prevent or treat specific health problems.

There are two problems with taking mega-doses of vitamins. First, there's rarely any scientific reason to take massive amounts of any vitamin (and then only under the guidance of your medical doctor), so you're probably just wasting money. And second, you can actually develop health problems if you mega-dose with some vitamins. Usually, the problems are reversible if you stop taking the mega-doses, but not always, so if you realize you've been taking a vitamin in a large dose, please contact your doctor right away.

Which Vitamins Are Bad for Me When Taken in Large Doses?

The Food and Nutrition Board of the Health and Medicine Division of the National Academies of Science, Engineering and Medicine has established Tolerable Upper Intake Levels (UL) for all vitamins and minerals.

The UL is the highest level of daily intake of a nutrient that's not going to pose any risks to a healthy person. 

Here's a look at the ULs for all the vitamins and what can happen if you take too much:

Vitamin A

Vitamin A is essential for normal vision, cell development, and immune system function. Adults need about 700 to 900 micrograms (mcg) per day, and it's found in liver, fish, meat, dairy products, and colorful fruits and veggies.

 

The UL for vitamin A by age: 
0-3 years: 600 mcg 
4-8 years: 900 mcg 
9-13 years: 1,700 mcg 
14-18 years: 2,800 mcg
Adults: 3,000  mcg

Since Vitamin A is a fat-soluble vitamin, it's easy for your body to store so it can accumulate over time. Long-term intakes of excessive amounts of vitamin A can cause intracranial pressure, dizziness, nausea, liver damage, headaches, rash, pain in your joints and bones, coma, and even death. 

Vitamin C

Vitamin C is needed for strong connective tissue and immune system function. It's also an antioxidant that can help prevent damage from free radicals. The average adult needs about 75 to 90 milligrams (mg) per day. Vitamin C is found in many fruits and vegetables, but people often take vitamin C supplements hoping they'll help ward off colds and flu.

Th ULs for Vitamin C by age:

0-12 months: unknown
1-3 years: 400 mg
4-8 years: 650 mg
9-13 years: 1,200 mg
14-18 years: 1,800 mg
​Adults: 2,000 mg

Taking large amounts of vitamin C isn't life-threatening, but it can cause diarrhea, nausea, and abdominal cramps and has been linked to kidney stones.

 

Vitamin D

Vitamin D helps your body absorb and utilize calcium, so if you don't get enough vitamin D you run the risk of weakened bones and osteoporosis, among other things. Most adults need 600 International Units (IU) every day. You don't get much vitamin D from food, but your body makes it after your skin is exposed to sunlight. Vitamin D is a popular supplement, but you can get too much if you mega-dose every day.

The ULs for Vitamin D by age:

0-6 months: 1,000 IU
7-12 months: 1,500 IU
1-3 years: 2,500 IU
4-8 years: 3,000 IU
9+ years: 4,000 IU

Taking too much vitamin D in the form of supplements can raise your blood levels of calcium, which can be bad for your heart and kidneys. You won't get too much vitamin D from excessive sun exposure, and it's extremely difficult to get too much vitamin D from your diet. An adult needs about 15 mg per day.

Vitamin E

Your body needs vitamin E for normal immune system function, and it also works as an antioxidant and helps prevent blood clots from forming in your blood vessels. It's found in a variety of foods, but mostly in nuts, seeds, and green vegetables. The average adult needs about 15 mg per day.

The ULs for Vitamin E by age:

0-6 months: unknown
7-12 months: unknown
1-3 years: 200 mg
4-8 years: 300 mg
9-13 years: 600 mg
14-18 years: 800 mg
​Adults: 1,000 mg

Taking too much vitamin E can increase your risk of bleeding, which is especially important if you're at an increased risk of stroke or take blood-thinning medications.

Niacin

Niacin helps convert the foods you eat into the energy your body needs to do everything you do. Deficiency is rare because it's found in a large variety of foods, but it's also sold as a supplement that's often used to manage cholesterol levels.  

The ULs for Niacin by age:

0-6 months: unknown
7-12 months: unknown
1-3 years: 10 mg
4-8 years: 15 mg
9-13 years: 20 mg
14-18 years: 30 mg
​Adults: 35 mg

Taking large amounts of niacin can lead to liver damage and affect blood sugar levels in people who have diabetes. In the short term, taking a large dose of niacin causes a niacin flush, which while not harmful, is uncomfortable and can be scary.

Vitamin B-6

Your body needs vitamin B-6 to help convert protein and sugar into energy, and it's essential for the production of hemoglobin and nervous system function. The average adult needs about 1.3 mg per day. It's pretty tough to have a B-6 deficiency, so supplementation isn't needed, but, it has been used to reduce homocysteine levels and to help treat depression and carpal tunnel syndrome

The ULs for Vitamin B-6 by age:

0-6 months: unknown
7-12 months: unknown
1-3 years: 30 mg
4-8 years: 40 mg
9-13 years: 60 mg
14-18 years: 80 mg
​Adults: 100 mg

Long-term use of vitamin B-6 supplements can cause nerve damage, skin lesions, nausea, and light sensitivity.

Folic Acid

Folic acid is a synthetic form of folate, a B-complex vitamin that's essential for making DNA, cell division and growth. Folate is found in fruits and green vegetables, while folic acid is often used to fortify cereals and bread. The average adult needs about 400 mcg every day, but it's also sold as a dietary supplement.

The ULs for Folic Acid by age:

0-6 months: unknown
7-12 months: unknown
1-3 years: 300 mcg
4-8 years: 400 mcg
9-13 years: 600 mcg
14-18 years: 800 mcg
​Adults: 1,000 mcg

Taking large amounts of folic acid may mask a vitamin B-12 deficiency that can lead to nerve damage. It's also possible that large amounts of folic acid might increase the risk of colorectal cancer.

Choline

Choline is a B-complex vitamin that your body needs for several biological processes and you need it to produce a brain chemical called acetylcholine. The average adult needs around 500 mg per day.

The ULs for Choline by age

0-6 months: unknown
7-12 months: unknown
1-8 years: 1,000 mg
9-13 years: 2,000 mg
14-18 years: 3,000 mg
​Adults: 3,500 mg

Taking too much choline on a daily basis can result in a fishy body odor, excessive sweating, low blood pressure and liver problems.

What About All the Other Vitamins?

The Food and Nutrition Board hasn't set ULs for vitamin K, thiamin, riboflavin, vitamin B-12, pantothenic acids or beta-carotene (a plant precursor of vitamin A). That doesn't mean it's OK to take huge mega-doses, just that tolerance levels haven't been determined yet. 

Vitamin Supplement Safety

Here are a few important tips to keep in mind if you want to take any vitamins as supplements:

  • Speak with your doctor if you're thinking about taking a vitamin or dietary supplement for a particular medical condition.
  • If you do take supplements, please follow the label directions, unless your doctor has told you otherwise.
  • Keep all vitamin bottles out of the reach of little kids.
  • Remember that taking supplements won't fix an unhealthy diet so keep your focus on eating a balanced diet including lots of fruits, vegetables, and whole grains.

Sources:

National Institutes of Health Office of Dietary Supplements. "Folate Dietary Supplement Fact Sheet." Updated April 20, 2016. 

National Institutes of Health Office of Dietary Supplements. "Vitamin A Fact Sheet for Health Professionals." Updated August 31, 2016. 

National Institutes of Health Office of Dietary Supplements. "Vitamin C Fact Sheet for Health Professionals." Updated February 11, 2016. 

National Institutes of Health Office of Dietary Supplements. "Vitamin D Fact Sheet for Health Professionals." Updated February 11, 2016. 

National Institutes of Health Office of Dietary Supplements. "Vitamin E Fact Sheet for Health Professionals." Updated August 31, 2016. 

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