Question: Why should I take vitamins?
Answer: People tend to take vitamins for one or two reasons:
  1. They have a vitamin deficiency (their body has too little of the vitamin)
  2. They are taking it to prevent or avoid a health condition

The most common groups of people with specific vitamin vitamin deficiencies are…

Vegetarian or vegan diet – Vitamin B12

Obesity – Vitamin D

Cystic Fibrosis – Vitamins A, D, E, K

Smoking or second-hand smoke – Vitamin C

Inflammatory bowel disease, short-gut syndrome, celiac disease – Folate, Vitamin B12, and Vitamins A, D, E, K

Some medications can cause vitamin deficiencies as well. Some common examples include: 

Vitamin D deficiency

  • Antacids (for heartburn)
  • Anti-seizure medications
  • Corticosteroids (i.e. prednisone)

Folate (vitamin B9) deficiency 

  • Methotrexate
  • Sulfasalazine
  • Trimethoprim

There is not a great deal of evidence that vitamins can be helpful in preventing disease. However, there is evidence to suggest:

  • Low-dose calcium and vitamin D supplements can lower risk of fractures and bone loss
  • Low-dose multivitamins seem to reduce risk of cancer, particularly in men with vitamin deficiencies or a history of cancer. The same effect has not been seen in women so far
  • Vitamin deficiencies are more likely in adults over the age of 65, particularly vitamin B12
  • Multivitamin use may have some short-term slowing of cognitive decline


Are there risks with taking a vitamin?

There are some vitamins where build-up in the body can cause toxicity. These include:

  • Vitamin A
  • Vitamin D (although it is rare to get to dangerous levels)
  • Vitamin E
  • Vitamin K
  • There is evidence that taking high doses of β-carotene (a type of vitamin A), vitamin E, and folic acid (vitamin B9) can cause harm.

This is not intended to scare folks away from taking them, as some people really do better taking these vitamins. But it does mean that those vitamins should be started after first discussing it with your primary care provider, so that you can get some guidance on how to take them safely at a helpful dose, and your provider can keep an eye on everything as well.


What should I be looking for?

The vitamin aisle can be pretty intimidating. Keep the following in mind when choosing an item there:

  • Make sure that the dose you are looking for is appropriate for you. Ask your doctor or pharmacist if you are unsure how much to take.
  • Make sure what you are buying is what it claims to be. Since supplements are not checked by the FDA, it is worthwhile to make sure the item only contains listed ingredients, and at the amounts/doses they claim. How can you do this?

Look for an NSF-verification mark, a USP Verified mark, or a mark (as seen below). These laboratories independently double-check ingredients and that the listed dose is what each tablet/capsule/powder contains.

Prepared by Ailish O’Sullivan PharmD Candidate 2020



  • FDA: Dietary Supplement Products & Ingredients; current as of 2/5/2020
  • Diab L, Krebs NF. Vitamin Excess and Deficiency. Pediatr Rev. 2018 Apr;39(4):161-179. doi: 10.1542/pir.2016-0068. PMID: 29610425.
  • Rautiainen S, Manson JE, Lichtenstein AH, Sesso HD. Dietary supplements and disease prevention – a global overview. Nat Rev Endocrinol. 2016 Jul;12(7):407-20. doi: 10.1038/nrendo.2016.54. Epub 2016 May 6. PMID: 27150288.