Is Too Much of a Multivitamin a Bad Thing?

Healthy individuals can easily get enough vitamin C through diet alone. In fact, based on a 2000-calorie diet for healthy adults, half of one 2.5-oz package of Kellogg’s Fruity Snacks provides 100% daily value (DV) of vitamin C. If you ate the entire package, it would provide 200% DV.

Is there a ramification for overdosing on vitamins like this?

If a patient is deficient in vitamins or minerals, diet-based solutions should be recommended first because they can provide many bioactive compounds and dietary fiber not found in supplements. If a patient isn’t deficient in vitamins or minerals, there’s insufficient data to suggest benefit from taking more than the daily recommended allowance of certain vitamin or mineral supplements.¹

Vitamin C, vitamin B12, thiamin, niacin, riboflavin, tryptophan, pantothenic acid, biotin, and folic acid are all water-soluble vitamins and nutrients. Although the body adapts by absorbing only what it needs and excretes the excess in the urine, excretion decreases when study participants fast.²

Even though they aren’t stored in the body, water-soluble nutrients can’t be presumed safe. In fact, too much vitamin B6 can cause nerve problems, too much vitamin C can cause kidney stones, and too much folic acid may mask vitamin B12 deficiency.²

In contrast with water-soluble nutrients, fat-soluble vitamins like A, D, E, and K can be stored in body tissues and accumulate to dangerous levels over time, potentially leading to hypervitaminosis, or excess amounts of a vitamin in the body. Too much vitamin A can cause birth defects, too much vitamin E can increase of hemorrhaging, and too much vitamin K can lessen or reverse the effect of blood thinners like warfarin and prevent normal blood clotting.²

How multivitamin overdose affects different parts of the body is displayed here³:

Body Part

Effects

Bladder and kidneys

Cloudy urine, frequent urination, or increased urine amount

Eyes, ears, nose, mouth, and throat

Dry, cracking lips (from long-term overdose), eye irritation, or increased sensitivity to light (for eyes)

Heart and blood

Irregular or rapid heartbeat

Muscles and joints

Bone, joint, or muscle pain, or muscle weakness

Nervous system

Confusion, convulsions (seizures), fainting, fatigue, headache, mental changes, mood changes, or irritability

Skin and hair

Niacin overdose: Flushing (reddened skin)

Long-term overdose: Skin sensitivity; hair loss; dry, cracking skin; itching, burning skin; or rash, yellow-orange areas of skin

Stomach and intestines

Iron or calcium overdose: Appetite loss, constipation,

Long-term overdose: Diarrhea (possibly bloody), nausea and vomiting, stomach pain, or weight loss

Patients should consult with their physician or pharmacist before taking any vitamins. Multivitamins can interact with certain medications and may need to be separated by 2 or more hours, or need to be taken on a consistent basis.

References

1. American Heart Association. Vitamin supplements: healthy or hoax? heart.org/HEARTORG/Conditions/Vitamin-Supplements-Healthy-or-Hoax_UCM_432104_Article.jsp#.V7vMbpgrLIU. Accessed August 24, 2016.

2. WebMd. Know the difference between fat- and water-soluble nutrients. webmd.com/vitamins-and-supplements/nutrition-vitamins-11/fat-water-nutrient?page=1. Accessed August 24, 2016.

3. MedlinePlus. Multiple vitamin overdose. nlm.nih.gov/medlineplus/ency/article/002596.htm. Accessed August 24, 2016.