How to Avoid an Upset Stomach From Multivitamins

According to the Council for Responsible Nutrition, a whopping 75 percent of Americans take supplements, which help fill in any small nutritional gaps in the diet. Vitamins and minerals are the largest category of supplements consumed, but what if those vitamins upset stomachs?

An October 2015 study in the ​New England Journal of Medicine​ reported that abdominal symptoms, such as nausea, vomiting, and abdominal pain, were frequently associated with products that contain iron or potassium.

​Read more:​ The 10 Best Supplements

Some vitamins upset stomach acid levels and aren't a good idea if you're eating to beat reflux. Vitamin C in high doses is a prime culprit here, as the vitamin is naturally acidic (it's chemical name is ascorbic acid). A January 2018 study in the ​Korean Journal of Physiology and Pharmacology​ showed that stomach acid output was increased by ascorbic acid in rats, while the non-acidic "ascorbate" form reduced stomach acidity.

This seems to fit with human research done some years ago and published in the January 2006 issue of ​Advanced Therapy​, which compared the experiences of 50 people who took 1,000 milligrams of ascorbic aid or the same dose of Ester-C, which is a commercial ascorbate preparation. Fewer people reported heartburn-type symptoms with Ester-C than with ascorbic acid.

If you want to avoid multivitamin stomach pain and nausea, you could pick one that is iron-free, or at least check the label and avoid iron sulfate, also called ferrous sulfate. A meta-analysis of randomized controlled trials in the February 2015 edition of ​PLOS One​ found that ferrous sulfate is particularly likely to cause gastrointestinal side effects. However, the extended-release form of ferrous sulfate is much better tolerated, according to an April 2013 review in ​Current Medical Research and Opinion.​

A March 2019 study in the E​uropean Journal of Obstetrics, Gynecology and Reproductive Biology​ found that amino acid chelated iron was also a better-tolerated form of iron.

You may be wondering, at what age should you take multivitamins? It turns out that being at both ends of the spectrum age-wise can increase the likelihood that you might need a supplement according to the Academy of Nutrition and Dietetics. For example vitamin D can be a concern among breast-fed babies, requiring that infants be given a vitamin-drop supplement, while adolescent girls might need additional iron.

Seniors can also find it difficult to get enough vitamin D and may also struggle to get enough vitamin B12. The Academy of Nutrition and Dietetics reports that getting B12 as part of a multivitamin can help raise B12 in the blood of older people. Whether an older individual or a child, people of all ages can have vitamins and minerals upset their stomachs.

​Read more:​ The 12 Best Natural Remedies for an Upset Stomach

According to the Cleveland Clinic, vitamins can upset stomachs by being taken at the wrong time. It's wise to take vitamins with food as it increases absorption of the nutrients while decreasing your risk of experiencing gastrointestinal distress.

Making sure your meal contains some fat —vegetable oil, nuts and oily fish are among the healthiest fat sources — will help the fat-soluble vitamins in a multivitamin be absorbed. A February 2015 study in the ​Journal of the Academy of Nutrition and Dietetics​ found that the level of fat-soluble vitamin D peaked 32 percent higher in the blood plasma of 50 people consuming fat-containing, rather than fat-free, meals.

​Read more:​ How to Determine if a Vitamin or Supplement Is Actually Right for You

The form of your supplement may make a big difference in how well you tolerate it. If you're looking for a multivitamin that won't cause nausea, then dissolvable, chewable, powder or gummy vitamins are a good bet, as they can be easier to digest than tablets.