5 Supplements That Can Cause Diarrhea (and How to Prevent It)

Supplements and vitamins are meant to promote health, but when you're experiencing GI problems, it's worth investigating if the booster could be the problem.
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If you take a vitamin or mineral supplement as part of your wellness routine, making healthy lifestyle choices is likely a priority for you. But when it comes to certain supplements, what you're putting into your body might actually stir up your gastrointestinal tract, leading to diarrhea.

Osmotic diarrhea occurs when you consume something that prevents proper water and electrolyte absorption, according to Clinical Methods: The History, Physical, and Laboratory Examinations.

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This type of diarrhea is most commonly associated with things we ingest, like certain supplements, Dr. Jouhourian says.

While it's not uncommon for people to experience a bout of diarrhea that subsides after a couple of days, even brief episodes of diarrhea can result in dehydration. That's why it's important to pinpoint what might be causing GI distress — such as these common supplements that cause diarrhea — and take steps to prevent it.

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1. Vitamin C

Vitamin C is a water-soluble nutrient, which means it can't be stored in the body for later use, and it's important to meet your daily recommended amount for it, per the National Cancer Institute. For adults, it's recommended to get 65 milligrams to 90 milligrams per day, according to the Mayo Clinic.

The upper limit, or the maximum amount you should have in any given day, is 2,000 milligrams. Megadoses of C can cause diarrhea as well as vomiting, cramps, nausea and other symptoms. But it's rare to get that much vitamin C through diet alone, Dr. Jouhourian says.

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2. Zinc

Research suggests that zinc might play a role in immune function, including promoting normal development and immune cell function, and preventing inflammation, according to a May 2008 paper in Molecular Medicine.

The recommended intakes for people assigned female and male are 8 milligrams and 11 milligrams, respectively, according to the National Institutes of Health (NIH). While zinc is found in almost all multivitamin supplements, most people get what they need from foods, including oysters, red meat, fortified cereals, beans, nuts, whole grains and some dairy products, according to the NIH.

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Getting too much zinc can bring excess water into the intestine, contributing to diarrhea, Dr. Jouhourian says.

But like with vitamin C, most people are getting adequate amounts, she says. "But that may change if more people take zinc to fight infection like COVID-19," Dr. Jouhourian says, noting there isn't research to suggest zinc protects against the coronavirus.

3. Fish Oil

Omega-3 fatty acids — found in fatty fish — are associated with heart health, reduced inflammation and improved cognition, according to the NIH. But when it comes to reaping those benefits from a fish oil supplement, the results are mixed.

For example, researchers did not find that omega-3 supplements reduced heart attacks, strokes or deaths in people without known risk factors, according to a November 2018 paper in the ​New England Journal of Medicine​. But researchers also found that those who didn't eat fish but took a supplement might reduce their risk of heart disease, according to Harvard Health Publishing.

That said, people who take a fish oil supplement may experience "slippery" poop, and in some cases, diarrhea, Jouhourian says. That's because fish oil contains a lot of fat, which essentially serves as a lubricant in the GI tract.

"Fish oil is similar to a stool softener, but it doesn't necessarily soften it — it's like a slip and slide." And if you take too much, it could lead to diarrhea, she says.

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4. Magnesium

Magnesium is a crucial nutrient for protein synthesis, muscle and nerve function and blood pressure regulation, according to the NIH. Magnesium is found in leafy green vegetables (think: spinach, kale and chard), legumes, nuts, seeds and whole grains.

The recommended daily intake is 320 milligrams for people assigned female at birth and 420 milligrams for people assigned male at birth, according to the NIH. And more often than not, people can hit those amounts from their diet.

"A lot of people might take magnesium for their immune system or cardiovascular health," Dr. Jouhourian says. And for those who have a cardiac arrhythmia and are taking magnesium, for example, diarrhea might be an issue, she says. Their doctors might prescribe an anti-diarrhea medication like Imodium.

Antacids with magnesium might also cause diarrhea, according to the U.S. National Library of Medicine.

5. Laxatives

This might go without saying: Laxatives are designed to cause diarrhea. Laxatives work by pulling water into the gut or causing the intestinal muscle to contract, according to the U.S. National Library of Medicine.

There are times when doctors might recommend a laxative, Dr. Jouhourian says, for reasons like constipation relief.

"It's OK to take a laxative here and there," Dr. Jouhourian says. "But they shouldn't be taken every day and should be taken under the guidance of a doctor." What can be dangerous and never recommended, she says, is taking a laxative for weight loss.

Taking a laxative for weight loss can lead to severe health issues, according to the National Eating Disorders Association (NEDA), such as:

  • Electrolyte and mineral imbalances, which can cause organ dysfunction
  • Severe dehydration, which can lead to kidney damage, tremors, weakness, fainting and, in some cases, death
  • Laxative dependency, which happens when the colon stops reacting to recommended doses of laxatives and requires larger amounts to produce bowel movements
  • Internal organ damage
  • Increased risk of colon cancer

Warning

If you or someone you know is struggling with an eating disorder or disordered eating, help is available. Please visit the National Eating Disorder Association for resources.

Tips to Avoid Diarrhea

If your supplement is sending you running for the bathroom, there are measures you can take to mitigate those effects.

1. Split Your Supplement Doses in Half

Spreading out your supplement dose can help ease any diarrhea you may be experiencing.

For example, you might try splitting your pill in half and taking one in the morning and one in the evening, Dr. Jouhourian says.

2. Take Your Supplement After Exercise

People who exercise are probably no stranger to the effects movement can take on their GI tracts. In fact, some 30 to 50 percent of athletes experience intestinal problems related to exercise, according to a May 2014 review in Sports Medicine.

"Exercise notoriously gets things going," Dr. Jouhourian says. She recommends taking a supplement after a workout, and perhaps more importantly, while eating, which can help settle the stomach.

3. Avoid Fake Sugars

Regardless of whether you're taking a supplement that might cause diarrhea, fake sugars — osmotic stimulants — can lead to or worsen diarrhea, Dr. Jouhourian says. It's best to read labels and avoid polyols or sugar alcohols.

"The key with diarrhea is [avoiding] the culprit," she says.

4. Focus On Fiber

Fiber can be a little tricky, Dr. Jouhourian says. Eating the right amount — 25 grams to 38 grams per day, according to the Academy of Nutrition and Dietetics — will keep your GI tract regular. But too much or too little fiber can lead to constipation or diarrhea.

In addition to eating enough fiber, make sure to stay hydrated. Dr. Jouhourian recommends drinking 64 ounces a day and more if you're physically active.

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