Isaac Robertson
Published by Isaac Robertson
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: May 26, 2021

Millions of people around the world take vitamins as a part of their daily nutrition.

And it seems like everything is vitamin-enriched, from bottled water to orange juice and fortified foods.

This is great, and it may seem as if all your needs are covered, but you can quickly go overboard and cause a vitamin overdose.

With our resident dietitian, we came up with everything you need to know about taking too much vitamin.

4 Signs You've Taken Too Many Vitamins

A sleep deprived person

Researchers still aren’t sure whether routinely taking a little bit too many vitamin supplements (and I don't mean a megadose) can create severe issues.

However, you can recognize some subtle signs and hints of concern.

These mild symptoms of taking too many vitamins and minerals may include:

  • Difficulty sleeping
  • Difficulty concentrating
  • Nerve problems such as numbness or tingling
  • Feeling irritable

Of course, this all depends on specific vitamins you're taking too much of.

Moreover, over fortification of our foods should be a much bigger concern.

Food producers have taken out fat, sugar, or salt from the foods, but they’re packing it with vitamin D, probiotics, or omega-3 fats — whatever dietary supplements are fashionable at the moment.

This means that users can’t possibly know how much vitamins and minerals they’re consuming during a day, which results in dietary imbalances.

"I have not seen someone off the street who was taking a toxic level of vitamin A or D -- those are very unusual. What I'm more likely to see is a person with a dosing level of supplements that's higher than optimal." — David Katz, MD, director of the Yale University Prevention Research Center in New Haven, CT.

Potential Risks of Taking Too Many Vitamins

Different vitamins on yellow background

When consumed naturally through foods, vitamins and minerals don’t usually cause harm, even when consumed in large amounts.

However, when you take them in concentrated doses in the form of vitamin supplements, it’s easy to take too much and cause negative health outcomes.

For discussion purposes, we’ll divide the potential risks of too much vitamins based on whether they are water or fat-soluble.

There are 13 known vitamins which are divided into two groups:

  • Fat-soluble vitamins stored in our bodies' fat tissues. These are vitamins, A, D, E, K, which may accumulate in our body and cause toxicity and severe side effects in some rare cases.

Water-soluble vitamins are excreted through urine and aren't stored in our bodies.

These are vitamin C and all B vitamins. They're not likely to cause harm or severe side effects even if taken in high doses. But taking megadoses of this vitamin group can cause nerve and liver damage.

Possible Side Effects of Fat-Soluble Vitamins

A person holding a pill and a water on the other hand

As I mentioned, the four fat-soluble vitamins (Vitamin A, Vitamin D, Vitamin E, Vitamin K)

can accumulate in your body's tissues and cause some severe health issues when taken at high doses, especially if you take them over long periods.

Vitamin K is the only one from this group that has a low potential for toxicity.

Still, the remaining fat-soluble vitamins have the potential to cause some serious issues at high doses.

Some side effects caused by the overconsumption of fat-soluble vitamins include:

  • Vitamin A toxicity, known as hypervitaminosis A, can happen when eating too many vitamin-A-rich foods, but it's more often caused by taking too much vitamin supplement. Hypervitaminosis A symptoms include increased intracranial pressure, nausea, coma, and even death.
  • Vitamin D toxicity can lead to appetite and weight loss, as well as irregular heartbeat. Too much vitamin D supplements can also raise blood calcium levels, leading to organ damage [1].
  • Vitamin E can cause hemorrhages, interfere with blood clotting, and lead to hemorrhagic stroke.

Vitamin K has a low potential for toxicity, but it can still interact with certain medications, such as antibiotics and warfarin.

Possible Side Effects of Water-Soluble Vitamins

A water soluble vitamin inside a glass of water

Water-soluble vitamins (Vitamin C and B Vitamins) may not be stored in our bodies, but taking too much of them can still cause adverse effects, some of which can be incredibly dangerous.

However, similarly to vitamin K, vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B5 (pantothenic acid), vitamin B7 (biotin), and vitamin B12 (cobalamin) have low toxicity levels but can interact with medications and interfere with blood testing results.

But, when taken in high doses, these water-soluble vitamins can cause some adverse side effects:

  • Vitamin C has low toxicity, but high doses can cause gastrointestinal disturbances, such as nausea, vomiting, diarrhea, and cramps. You can also experience migraines if you take 6 grams of this vitamin a day.
  • Vitamin B3 (niacin) can lead to impaired vision, abdominal pain, high blood pressure, and liver damage if you consume it in doses of 1–3 grams a day.
  • Vitamin B6 (pyridoxine) can cause nausea, heartburn, sensitivity to light, skin lesions, and severe neurological symptoms if you take it in doses of 1–6 grams a day [2].
  • Vitamin B9 (folate/folic acid) could potentially affect your mental function, negatively impact your immune system, and mask a potentially severe vitamin B12 deficiency if taken in high doses in the form of folic acid.

Please remember that these overdose symptoms and side effects were observed in healthy people who have been taking high doses of these vitamins.

People with certain health conditions may experience even more serious reactions.

Let’s take vitamin C as an example.

Excessive amounts of the vitamin aren’t likely to cause toxicity in healthy people, but they might lead to tissue damage and fatal heart abnormalities in people with iron storage disorder.

Can Taking Too Many Vitamins Be Deadly?

A woman thinking about the risks of vitamins on her hand

Although it’s extremely rare to die from a vitamin overdose, there have been some cases of vitamin toxicity-related deaths.

To paint you a word picture —  hypervitaminosis A can be caused by a single 200mg dose of vitamin A. It can also be caused by chronic use of over ten times the recommended daily intake.

The toxic levels cause increased spinal fluid pressure, coma, and fatal organ damage.

Moreover, taking megadoses of vitamin D, over 50,000 IU a day, for long periods can cause high blood levels of calcium (hypercalcemia), which can lead to death.

Overdosing on other vitamins can also cause side effects that can lead to death.

Researchers have discovered that taking very high doses of over 5 grams of extended-release niacin can lead to a buildup of acid in body fluids and acute liver failure — both of which can have deadly outcomes.

Of course, an occasional high dosage of vitamins won't kill you; these examples are related to taking exceptionally high doses of vitamins.

Nevertheless, you should always be careful when taking any dietary supplement.

How To Safely Take Vitamins?

A woman looking at the vitamins on her hand

Most vitamin bottles provide recommendations on how much vitamin to take a day, vitamin needs can vary from person to person, so it's always best to consult your doctor.

In an ideal world, a balanced diet is the best way to get the nutrients your body needs.

However, people take a daily multivitamin for many reasons, such as age, medical conditions, genetic disorders, and diet restrictions.

Even though some vitamins can cause serious side effects and health issues, they’re usually safe to take as long as you use them responsibly.

Your doctor may recommend that you take more than the UL (tolerable upper intake levels) for certain nutrients to correct a deficiency in some circumstances.

Vitamin D deficiency is often treated with supplements that deliver over 50,000 IU of vitamin D or high-dose vitamin D injections, which is much more than the UL.

Can You Overdose On Vitamins? My Final Thoughts

While vitamins are generally safe, it is possible to overdose on them when taken in excess over long periods.

Even since trying gummy vitamins as a kid, I've been hooked on supplementing correctly. A healthy diet is crucial, but some vitamins are just hard to absorb from food.

Taking an additional vitamin in a supplement form is an excellent way to cover your needs, but always listen to your doctor's recommendations to avoid health issues.


References:

  1. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
  2. https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/

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