Vitamin D is consistently hailed as a crucial nutrient, essential for overall health and well-being. Is it possible that this heralded vitamin could also actually be the cause of an uncomfortable, inconvenient, and not-generally-talked-about in genteel social situations, health concern?

That’s right, we’re talking about diarrhea. And for some people, there is an association between diarrhea and vitamin D, likely those with too much vitamin D in their blood.

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Despite vitamin D’s long list of benefits, starting with its role as necessary in various bodily functions, there have been some reports of individuals experiencing gastrointestinal issues thought to be related to high vitamin D supplements or increased intake from food sources.

In this week’s blog, we’ll explore the potential association between excessive vitamin D and diarrhea and provide insights into how this potential connection can be nipped in the butt, um, we meant nipped in the bud.


The ABC’s of Vitamin D 

Let’s start with the many benefits of vitamin D as scientists continue to unlock new reasons to ensure your body is sufficient, at the very least, if not optimal, in your vitamin D blood levels. For starters, there are the foundational functions that vitamin D helps make happen, for example, improving your body’s ability to absorb calcium and phosphorous, which in turn help build and maintain strong bones and sturdy teeth.

Vitamin D is also an anti-inflammatory warrior, moderating your body’s inflammation system by regulating the manufacture of inflammatory cytokines and immune cells, one reason why scientists have become fascinated with vitamin D’s potential role in protecting against some immune-related diseases, such as COVID.

There’s also research that suggests it’s the lack of vitamin D that can do a great deal of damage several areas. Low vitamin D levels (especially deficiencies) have been associated with heart health issues (such as heart palpitations, hypertension and even sudden cardiac death),  women’s issues (including pregnancy and menstrual cycle regularity), skin problems (e.g., bruising and skin rashes), urinary tract infections (UTIs), gastrointestinal problems and many other potential concerns.

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Given all the issues potentially connected to low vitamin D blood levels, you may be surprised to learn that so many of us are simply not getting enough vitamin D. Worldwide, the issue is considered serious, with estimates that half the population is vitamin D-insufficient and here in the U.S., 35% of adults have a vitamin D  deficiency.

In fact, because so many Americans are low in vitamin D, the science-based, Dietary Guidelines for Americans, considered the foundation for nutritional public policy in the U.S., positions the problem as a public health concern.

There are two major forms of vitamin D: D2 (ergocalciferol), which is plant-based and D3 (cholecalciferol), from animal sources. Here are the four main ways to obtain vitamin D.

  1. From the sun—when your skin is exposed to the ultraviolet (UV) rays from sunlight, your body converts those rays into vitamin D3. While this is the best natural source for vitamin D, too much sun exposure can lead to skin cancer; therefore, avoid prolonged (especially unprotected) exposure to the sun and safeguard yourself with sunscreen (SPF 15 or higher) and protective clothing.
  2. From conventional/fortified food—there aren’t a lot of food options for getting optimal levels of vitamin D. You can find vitamin D in salmon and other fatty fish, beef liver, egg yolks, and some mushrooms. Check labels on orange juice, milk (plant and dairy), and cereals as many of these foods have been fortified with vitamin D.
  3. From dietary supplements—Whether you’re choosing multivitamins, combination vitamins (e.g., vitamin D with calcium) or single letter (in this case vitamin D) supplements, getting vitamin D from supplements is a perfectly reasonable option, especially if you’re not regularly eating the kinds of foods that confer vitamin D and/or spending time outdoors. Even if you are, many of us need to add D supplements to reach sufficient or optimal levels of this vitamin. Fortunately, there are numerous dietary supplement options, from brands, to a range of doses, and for vegetarians and vegans as well as for omnivores.
  4. High dose oral prescription drugs—There are circumstances whereby your doctor might prescribe a megadose (e.g., 50,000 IU weekly) prescription of an oral vitamin D in order to raise your vitamin D blood level out of deficiency or insufficiency. This option is usually not a long-term solution and should be monitored through testing and in consultation with your doctor.


Let’s Talk About Diarrhea, Shall We?

It may be a sensitive subject, but most of us have likely had diarrhea at some point in our lives. And some of us have it a lot. In fact, in the U.S., some estimates cite around 179 million cases of acute diarrhea a year—and that’s just one type of diarrhea.

Diarrhea is defined as loose, watery stools that are passed through your body (specifically through your anus) three or more times per day (or more frequently than normal based on the individual). Acute diarrhea typically lasts a day or two and resolves itself, whereas persistent diarrhea lasts between two and up to four weeks. Chronic diarrhea lasts at least 4 weeks, and can come and go, or be continual. Read more here.

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While diarrhea can be merely an annoyance—albeit a bit scary if you’re in a social situation and not sure you’ll make it to the bathroom in time—there are serious complications that can occur with diarrhea if not addressed.  For instance, diarrhea can lead to dehydration, malabsorption or malnourishment.

There’s a long, long list of reasons why diarrhea occurs, and here’s some of that list: an infection in the intestinal tract (bacterial, viral or parasitic organisms), digestive conditions (such as celiac, Crohn’s, or IBS), colon cancer, lactose intolerance, taking too many laxatives, medications (e.g., antibiotics, antacids with magnesium, cancer-fighting drugs), foods that irritate your digestive system, and stress or anxiety.

And yes, too much vitamin D might lead to diarrhea.   

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What Happens with Too Much Vitamin D Intake?

You can get too much of a good thing. Very high levels of vitamin D in your blood can cause all sorts of problems including nausea, vomiting, muscle weakness, confusion, pain, dehydration—and the list goes on. And yes, even diarrhea.

According to this article, excessive vitamin D levels are blood levels over 100 ng/mL while levels reaching 150 ng/mL and beyond are defined as hypervitaminosis D, a rare but potentially serious condition.  The only way to know if your numbers are too high is to get tested.

Interestingly, if you suspect that your high vitamin D levels are related to your diarrhea, vitamin D itself may not be the actual culprit, but rather the wingman. Here’s what we mean by that.

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Magnesium aides in vitamin D activation. And vitamin D helps increase calcium absorption efficiency. That’s one reason why companies sell supplements in combinations of vitamin D and calcium or vitamin D and magnesium. But here’s something to consider.

High doses of magnesium from dietary supplements or medications can lead to diarrhea, according to this fact sheet from the government’s Office of Dietary Supplements.

As for calcium, when it comes to gastrointestinal symptoms, including diarrhea, this article suggests that the main side effects of excessive intake of vitamin D are related to excessive calcium in the blood.

In other words, because of vitamin D’s impact on increasing levels of calcium in the blood, taking excessive amounts of vitamin D may also lead to high blood levels of calcium in the blood. Meaning that if you’re taking large doses of vitamin D, you might experience stomach pain, constipation, and yes, diarrhea, because of elevated calcium levels.

But before you throw away your vitamin D, magnesium or calcium supplements, be aware that all three are vital nutrients and the positive interconnections between them are beneficial to your health.

When it comes to vitamin D and diarrhea, keep these three things in mind:

  1. Not getting enough vitamin D is much more common than getting too much vitamin D. And according to this article, “Even when taking high dose vitamin D supplements, it’s unlikely that a healthy person’s blood vitamin D levels would come close to reaching excessive or toxic levels.” The post adds that most cases of vitamin D toxicity are due to either inappropriate supplement dosing or prescription errors. Some symptoms of vitamin D toxicity include confusion, lethargy, fatigue, muscle weakness and difficulty walking.
  2. There are numerous causes of diarrhea, and vitamin D, calcium or magnesium supplements are generally not the first suspects when it comes to diarrhea. Certainly not when taken in moderate amounts. To learn more about how much of each vitamin or mineral is recommended by the government, check here for vitamin D, here for calcium and here for magnesium. Keep in mind, however, that some people have reason to go beyond those recommendations. Have that discussion with your doctor.
  3. The simplest way to rule out whether your diarrhea is related to excessive amounts of vitamin D in your blood is to test how much vitamin D you have in your blood in the first place. Whether your vitamin D blood levels are too high or too low, either one can cause some serious health problems. If you want to know for sure if you’re in the “goldilocks” (just right!) range, test! Ask your doctor to order lab work, or take an at-home test, such as the one offered here by OmegaQuant.

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Bottom Line: Some people may have a medical reason for taking high doses of vitamin D, but if you think you’re in that group, don’t megadose on your own. Involve your doctor in that decision.

Test your vitamin D blood levels regularly to ensure they are in the right range and make changes as warranted if they’re too low or too high. If you have diarrhea and it doesn’t go away on its own, it’s time to talk with your doctor to determine a cause and to find ways to mitigate the problem. Sometimes a simple change in diet can make a difference.

These statements have not been evaluated by the Food and Drug Administration. This test is not intended to diagnose, treat, cure, prevent or mitigate any disease. This site does not offer medical advice, and nothing contained herein is intended to establish a doctor/patient relationship. OmegaQuant, LLC is regulated under the Clinical Laboratory improvement Amendments of 1988 (CLIA) and is qualified to perform high complexity clinical testing. The performance characteristics of this test were determined by OmegaQuant, LLC. It has not been cleared or approved by the U.S. Food and Drug Administration.

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