What do you think of when you hear the word “multivitamin?” Probably something positive; after all, we’re conditioned to take our vitamins from a young age with delicious Flintstone vitamins. Even as adults, we face the temptation of gummy multivitamins that make it hard to stop at the recommended serving size. Whatever it is that springs to mind, it’s probably correlated to improving your overall health—but what if this is a misconception? What if those vitamins you think are improving your health could actually be harming it?

“In some cases, taking vitamins can cause toxicity in individuals—especially if the person has a well-balanced diet already,” said Mary Chavez, Pharm.D., interim vice dean and professor and chair of pharmacy practice at the Texas A&M Health Science Center Irma Lerma Rangel College of Pharmacy.

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In contrast to this, though, there are some cases in which taking a vitamin is beneficial to your overall health: such as if you have a vitamin deficiency. No matter which end of the vitamin spectrum you fall on, it is important to consult your health care provider and pharmacist before adding a daily supplement to your diet.

To help us discern from whether a vitamin is helpful or quite the opposite, Chavez offers us some parameters on when it’s a good idea (or not) to use certain vitamins:

Visit with your physician

Determining whether or not taking a vitamin is right for you starts with visiting your primary care physician. Being familiar with your lifestyle and testing your blood during your annual physical will help your physician decide if you would benefit from adding a vitamin or supplement to your daily regimen.

When vitamins may be beneficial

“In most cases, with individuals who have normal, well-rounded diets, vitamins or supplements aren’t necessary,” Chavez notes. “But there are some situations when it may be helpful to take a vitamin or mineral.”

Your physician or pharmacist might recommend taking a vitamin or another supplement when:

  • You are on a restrictive diet
  • Are pregnant or are trying to become pregnant
  • Have a vitamin deficiency

If you have a diet that limits certain nutrients, such as a strict vegan lifestyle, your physician or pharmacist may recommend adding vitamin B12 to your daily regimen. Vitamin B12 promotes healthy red blood cells. Low levels can cause anemia, numbness and tingling of hands and feet, sore tongue, muscle weakness, memory loss and mental issues. Certain medical conditions and medication could cause some people to not absorb vitamin B12.

“For women who are pregnant or are attempting to conceive, folic acid is an important supplement to reduce the chances of a neural disorder in the fetus,” Chavez stated. “And pregnant women should also take iron supplements as recommended by an obstetrician or other health care provider.”

If you have a vitamin deficiency that is interfering with your overall health, your physician or pharmacist might recommend consuming that vitamin in pill form. The most common deficiencies are vitamins D, B12 and calcium. Supplementation with vitamin D and calcium may promote healthy bone structure and density in postmenopausal women. For individuals at increased risk for developing osteoporosis or osteopenia, the National Osteoporosis Foundation recommends taking a daily supplement of both.

The risks of vitamins

You’ll hear it time and time again: Smoking is bad for you. But when it comes to vitamins, smoking may contribute to an increased risk in developing lung cancer, especially when combined with regular intake of beta carotene and vitamin A, which are commonly present in multivitamins.

“In some cases, vitamins build up in people’s systems and can lead to severe toxicity,” Chavez warned. Vitamins that are more likely to cause toxicity are fat-soluble, as opposed to water-soluble, which are not stored in the body and must be replaced each day. Among fat-soluble vitamins, vitamins A, E, D and K are the most common.

Common side effects of toxicity to look for are:

  • Nausea
  • Vomiting
  • Headaches
  • Dizziness
  • Diarrhea
  • Death in extreme cases

Some vitamins may also interact with certain medications. For example, vitamin K can counteract blood-clotting medications. When deciding on whether or not a multi-vitamin is best for you, consult your physician or pharmacist to make sure that it won’t cause any harmful effects; and be sure to always include any vitamins, minerals or herbal supplements that you’re using in your medication list to avoid possible interactions.