Here’s What Happens to Your Body When You Start Taking Vitamins, Says an Expert Doctor

Updated: May 23, 2024

For anyone curious if taking a vitamin is worth it, a doctor and Cleveland Clinic nutritionist say vitamins can lead to noticeable changes.

Possibly thanks to the pandemic, there’s a common question about whether our long-held wellness practices have been doing as much for us as we’ve believed. One example is the way multivitamins, the dietary supplements used by approximately one-third of American adults according to the National Institutes of Health, have caused confusion in recent years. Some sources suggest that up to 86% of adults take vitamins and supplements, yet only 21% have a documented vitamin deficiency. We spoke with health experts to get a verdict on whether it’s necessary to take a vitamin, any difference you’ll notice, and how long that difference will take.

Samuel Mathis, MD, MBA, a board-certified family medicine doctor and assistant professor of family medicine at the University of Texas Medical Branch, says, “Whether or not someone sees a positive effect with taking a multivitamin is purely dependent on whether they have a deficiency in that vitamin.”

"With individual vitamins, side effects tend to occur more frequently due to their high concentration."
Samuel Mathis, MD, MBA
Board-certified family physician and Assistant Professor & Associate Director, Medical Student Education Program at University of Texas Medical Branch

Despite their popularity, no concrete evidence suggests multivitamins prevent or lessen the risks of major diseases. Instead, many experts consistently advocate that a healthy diet can naturally meet your vitamin needs. Julia Zumpano, RD, a registered dietitian with the Cleveland Clinic’s Center for Human Nutrition, evaluates her patients’ diets and supplement intake before recommending multivitamins. “A basic [multivitamin] is not harmful but may be unnecessary based on their current diet or supplement regimen,” Zumpano says. For this reason, always consult your healthcare provider to determine whether taking a multivitamin is right for you.

Ahead, both Zumpano and Dr. Mathis discuss what happens to your body when you start taking vitamins, who might benefit most, and the possible side effects.

Multivitamin basics

A multivitamin is a supplement typically available in tablet, capsule, or liquid form that combines a variety of essential vitamins and minerals—often vitamins A, C, D, E, and K and minerals like calcium, magnesium, and zinc. The composition of multivitamins can differ, but the aim is to provide a convenient source of nutrients that may not be sufficiently consumed through diet alone.

Zumpano works with Cleveland Clinic patients who may be undergoing medical treatment and therefore have a wide range of unique nutritional needs. With this in-depth expertise, a universal recommendation she makes is to select a multivitamin that is:

  • gender-specific
  • age-specific
  • verified through third-party testing
  • Harvard Health also suggests selecting a vitamin that features the United States Pharmacopeia (USP) seal of approval on its label. This seal guarantees that the multivitamin contains the ingredients and the amounts listed on the label.

What happens when you start taking vitamins for the first time?

VItamin C orange tablets backgroundimamember/Getty Images

When you start taking vitamins, the effects you experience can vary based on your specific nutritional needs, how well your body can absorb the nutrients, and which type of vitamin you’re starting. “For someone who is low on vitamin C, they will see the benefits of taking vitamin C pretty quickly,” Dr. Mathis shares. Those who have been vitamin C-deficient can observe improvements in fatigue, skin condition, and immune function.

“For other vitamins and minerals, the effects are slower and less obvious,” Dr. Mathis says.

A few factors should be considered to improve absorption:

  • Taking vitamins with mealsConsuming your vitamins with food can enhance their absorption. This is particularly true for fat-soluble vitamins like A, D, E, and K, which need to be accompanied by fat to dissolve properly. Some sources suggest between five and 10 grams can be an ideal amount of fat to help your body take in all that nutrition—think two eggs, a couple slices of cold salmon, or a few bites of avocado.
  • Choosing the proper form of the vitamin for better bioavailability: “Bioavailability” refers to the proportion of a nutrient that is absorbed from the diet and used for normal body functions. Some forms of vitamins are more easily absorbed and utilized by the body than others. For example, vitamin D3 is typically more effectively absorbed than vitamin D2.
  • Addressing any digestive issues that may impede nutrient uptake: Digestive problems, such as low stomach acid, celiac disease, or inflammatory bowel disease, can hinder the body’s ability to absorb vitamins and minerals from both food and supplements. Managing these conditions can help improve nutrient absorption, ensuring the body receives the full benefit of the vitamins you are taking.

How long does it take for vitamins to start affecting your body?

“It can take some vitamins four to six weeks before we start to see the effect or benefit,” Dr. Mathis says.

On the other hand, Zumpano says the timeframe for experiencing the benefits of a multivitamin can extend to two to three months, depending on how well your body absorbs the supplement.

Dr. Mathis suggests that patients should allow at least a month to evaluate whether the vitamin or supplement is making a difference. After this period, he says it may be worthwhile to take a break and compare the effects of being on the supplement, versus off of it (with your doctor’s OK, of course).

What happens to your body when you take a multivitamin every day?

Taking a multivitamin daily can help maintain good health and prevent nutrient deficiencies, especially if your diet doesn’t provide all the necessary nutrients. Long-term users often report fewer instances of common colds, thanks to the immune-boosting effects of vitamins like C and E. Additionally, consistent intake of vitamins B12 and D can support bone health and neurological functions.

What are the possible side effects of starting new vitamins?

The possible side effects of starting new vitamins depend on the vitamin you are taking. Dr. Mathis notes, “For a multivitamin, some individuals may experience changes in their bowel habits or an upset stomach.” He adds: “With individual vitamins, side effects tend to occur more frequently due to their high concentration.” If you’ve started a specific supplement like magnesium or iron, this might sound familiar.

Common side effects of starting a new vitamin include:

  • Stomachache
  • Nausea
  • Diarrhea
  • Constipation
  • Changes in urine color

Additionally, certain vitamins might elevate the risk of specific health issues. For example, high doses of vitamin C have been shown to increase the likelihood of developing kidney stones.

Zumpano highlights some less common, yet important, side effects to be mindful of, such as headaches, skin redness, itching, rash, anxiety, and allergic reactions. Should any of these occur, discontinue use and consult with your healthcare provider immediately.

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