Vitamin D is an essential nutrient that plays a vital role in many of our body’s functions, including digestion. While you’re likely aware that the “sunshine vitamin,” as D is nicknamed, is important for calcium absorption and strong bones, we’re going to guess that you may not know—or understand—how vitamin D affects our digestive health.

BLOG: Vitamin D Deficiency and Mortality

In today’s blog, we’ll explore the role vitamin D plays in digestion and discuss ways to ensure you are getting adequate levels of this important nutrient in your diet.


Background Information on Vitamin D

Especially in the past decade or so, the scientific community has taken a keen interest in studying the potential benefits of Vitamin D beyond its work in absorbing calcium and phosphorous, both of which help build strong bones and support teeth and gums.

There’s some research that associates low vitamin D levels with heart palpitations, a potential signal of heart arrhythmia, and other studies have linked vitamin D deficiency with heart problems including arterial hypertension, diabetes mellitus and even sudden cardiac death.

BLOG: How Does Vitamin D Affect Your Heart?

One meta-analysis of 30 randomized controlled trials suggested that vitamin D supplements served at >800 IU/daily significantly reduced blood pressure.  (There’s other research for vitamin D that is not as promising for heart health and you can read more here.)

Some emerging research finds vitamin D may help reduce the risk of some cancers. In fact, in observational studies, higher vitamin D levels have been consistently associated with reduced risk of colorectal cancer, for one, and most meta-analyses of observational studies have associated lower vitamin serum levels of vitamin D with higher overall cancer mortality. Not all research is positive, though. (Read more here.)

BLOG: Vitamin D Deficiency and Dementia

Other emerging research shows a potential role for vitamin D in sleep regulation, with low levels of the vitamin associated with sleep-related problems like insomnia and sleep apnea. And the March of Dimes identifies vitamin D as one of six key vitamins most important during pregnancy to aide in the baby’s growth and development.

VIDEO: Why Do You Need Vitamin D?


What About Gut Health?

Then there is the role of vitamin D and immune function (and inflammation) which is most relevant to today’s blog. Vitamin D is vital to your immune system’s proper function because it helps your immune system resist bacteria and viruses.

We’re bringing that up because of this little-known fact: 70 percent of the immune system is found in your gut, according this article posted on the California-based university’s health care system’s website. As it turns out, the microbiome and the immune system are “critically intertwined.”

If you’re not yet familiar with the term microbiome, be aware it’s one of science’s current hot topics, especially in the nutrition field. The microbiome is a diverse array of bacteria, fungi, viruses, and their genes that naturally live on our bodies and inside us, says the National Institute of Environmental Health Sciences.

BLOG: Should You Take Vitamin D2 or D3?

The gastrointestinal microbiome is the largest and most diverse reservoir of all the human body niches, according to this post.

A cross-sectional analysis published in Metabolism of 150 healthy adults showed that those study participants with higher vitamin D levels were associated with an abundance of gut microbes that are connected with good gut health.

Thus, the authors theorized that the maintenance of homeostasis seems to occur in part by interacting with the gut microbiota, further suggesting that inflammation is part of the relationship between the gut microbiota and vitamin D concentration.

BLOG: Can Vitamin D Deficiency Case Low White Blood Cell Count?

Part of vitamin D’s role in immune health is its potent anti-inflammatory properties. And some digestive issues are associated with inflammation.  So, you may rightly wonder, is vitamin D deficiency or low levels a potential risk factor for problematic gut health? Keep reading! (First, we need to explain about vitamin D levels.)


Vitamin D Levels

A public health concern. That’s what the Dietary Guidelines for Americans, the government’s gold standard recommendations for nutritional advice, calls the fact that so many Americans are low in vitamin D. Actually, it’s a worldwide concern, with some statistics showing that half the global population is vitamin D insufficient.

One reason why so many people are lacking in vitamin D is that there are limited conventional food options to obtain the nutrient. And many of these foods are fish, which some Americans seem not to care for. Although we’re not sure why.

Salmon is a great fatty fish-option, whether wild or farmed, for vitamin D as well as other important nutrients such as omega-3 EPA and DHA, which are also inflammation warriors.  A 3.5 ounce serving of farmed Atlantic salmon contains 66% (526 IU) of the daily value for vitamin D, according to this article. (Wild-caught salmon generally contains even higher percentages.)

BLOG: The 3 Best Ways to Boost Your Vitamin D Level

Other fish that are good sources for vitamin D include mackerel and halibut, respectively serving up vitamin D in reasonable percentages of the daily value (643 IU and 190 IU, per 3.5-ounce serving). There’s also tuna and trout, as well as sardines and herrings, the latter less likely to be enjoyed by Americans.

Beyond fish, there aren’t a lot of food options for getting enough vitamin D. Eggs (it’s the yolk, but the white contains protein), beef liver and cheese each have small amounts of vitamin D, as do mushrooms. Some mushroom growers expose mushrooms to ultraviolet light, which increases their vitamin D amounts.

There are some foods that are now fortified with vitamin D, like orange juice and milk, and some cereals and oatmeal, giving vegetarians and non-fish lovers a swimming chance at taking in vitamin D. The key, though, is checking the label to discover if the food is fortified with the sunshine vitamin, and with how much.

VIDEO: What is an Optimal Vitamin D Level?


Supplementation Strategies for Improving Digestive Health and Increasing Vitamin D Intake

The fact that getting vitamin D from food alone is difficult makes supplements an even more important option to consider. Especially for those who live in climates where it’s not always enjoyable to be out in the sun. That, and the fact that cancer-protecting sunscreen blocks out many of the UV rays that your body needs to produce its own vitamin D make dietary supplements quite the reasonable option.

Here’s another reason why so many of us don’t get the vitamin D benefits we need, even if we’re supplementing our diets with a vitamin D supplement. Vitamin D is a fat-soluble nutrient, which basically means that it doesn’t fully dissolve with water. So, when you take your vitamin D supplement, by all means, swallow it with water, but pair it with eating some fatty food to be sure it’s fully absorbed.

BLOG: How to Choose the Best Vitamin D Supplement

Government recommendations for vitamin D start at birth at 400 IU (10 mcg) daily and increase to 600 IU (15 mcg) from ages 1 – 70 years old, including pregnant and breastfeeding teens and women. After 70, the recommendations increase to 800 IU (20 mcg) daily.

Other experts believe this recommendation is too low to achieve all the potential benefits of vitamin D. For instance, the Endocrine Society has recommended intake of 1,500-2,000 IUs daily to reach adequate vitamin D levels.

Over-the-counter dietary supplements for vitamin D range in daily doses of 400 IU to 10,000 IU and prescription vitamin D is available in doses of 50,000 IU weekly. To put those doses into context, the National Academy of Medicine has identified the Tolerable Upper Intake Level—the maximum daily intake unlikely to cause harmful effects—for vitamin D as 4,000 IU daily for adults (and children ages 9+).

Still, other experts have suggested an even higher safe upper level of 10,000 IU daily, stating that “collectively, given the absence of toxicity in trials conducted in healthy adults of > or = 250 microg/d (10,000 IU vitamin D3) supports the confident selection of this value as the UL.”

We preach a more practical approach. Get your vitamin D blood levels tested, through an at-home test or with a doctor’s order for an in-person lab test.

The only way to know if what you’re getting is working is to determine your blood levels, which testing does.

At OmegaQuant, we’ve identified vitamin D blood levels as follows:

  • <10 ng/mL (deficient);
  • 10-20 ng/mL (insufficient);
  • 20-30 ng/mL (sufficient);
  • and >30-50 ng/mL (optimal).

Results >90 ng/mL might mean you’re getting too much vitamin D—and yes, you can get too much of a good thing. If not in the sweet spot (sufficient or optimal), you’ll want to consider dietary (including supplements) changes and/or get outside more. Once you reach sufficiency or optimal vitamin D levels, maintain your vitamin D regimen and retest every 6 months to be sure you remain in your preferred range. Keep your doctor involved with the results.

VIDEO: How Much Vitamin D Do You Need?


Health Effects of Low Vitamin D Intake

Are there consequences to vitamin d deficiency or insufficient vitamin D levels?

Low vitamin D is often associated with gut health problems (not to mention osteopenia or osteoporosis, elevated parathyroid hormone and an increased risk of falls and fractures).

This prospective case control study was conducted in 86 patients with chronic functional constipation (in simple terms, infrequent and painful bowel movements) that associated to intestinal motility disorders (meaning abnormal muscle and nerve contractions in the GI tract that interfere with normal digestive function.) This group was matched with 86 healthy subjects.

The study authors reported that patients with intestinal motility disorders had lower vitamin D levels and demonstrated a significant impairment of all health-related quality of life and psychological tests as compared to the control group, which significantly correlated with low vitamin D levels.

BLOG: Vitamin D Levels Around the World are LOW

The proportion of patients with intestinal motility disorders was more affected by constipation, abdominal pain, swelling, anxiety and depression symptoms as well as by quality-of-life issues, as compared to healthy subjects.

The authors advised that as vitamin D deficiency, anxiety and depression symptoms are commonly associated with chronic functional constipation, it’s important to routinely measure vitamin D serum levels in those patients.

They also noted that depression has been commonly observed in patients with the constipation variant of IBS.

Because of vitamin D’s recent recognition as an immunoregulator, there have been studies conducted on autoimmune disease and its anti-inflammatory effects.

This literature review noted that there has been evidence that vitamin D can regulate gastrointestinal inflammation, adding that previous studies demonstrated that vitamin D can impact the gut microbiome. The authors were interested in evaluating the effect of vitamin D in relation to inflammatory bowel disease (IBD) and the gut microbiome.

Among their findings: vitamin D deficiency is associated with the onset and activity of IBD and the risk of its malignant transformation. For example, a large study of over 3,000 patients with Crohn’s Disease (CD), a common form of IBD, and Ulcerative Colitis (another IBD condition) showed nearly one-third had a vitamin D deficiency.

BLOG: Vitamin D: Are You Getting Enough?

The review authors also reported that other cohort studies have found similar associations between CD and low vitamin D levels, including a cross-sectional study that not only found lower serum levels for vitamin D linked to higher levels of fecal calprotectin, a marker for intestinal inflammation, and those study authors suggested vitamin D might have value in treating intestinal inflammation. There have been few clinical trials to support vitamin D as a treatment in this area, and the review authors believe further research is necessary for using vitamin D as an adjunct therapy for IBD patients.

This scientific article advises that vitamin D deficiency is more common among those with IBD, but it’s unclear if the relationship is causative or a result of inflammation. Their emerging research shows, say the authors, that vitamin D deficiency may be implicated in the severity of IBD, if not the etiology.

They conclude by stating that vitamin D plays a significant role in the maintenance of gastrointestinal barrier integrity, surveillance of the gut microbiota and inflammatory immune responses. These mechanisms are important in both preventing the development of IBD and ameliorating symptoms of the disease.

The GI Society explains that those with a bowel disease, including Crohn’s, untreated celiac, pancreatic enzyme insufficiency, and others, may have trouble absorbing dietary fat, leaving them at greater risk for vitamin D deficiency.

According to the post, for more than 20 years, studies have demonstrated some protection from vitamin D in risk reduction of another gastrointestinal disease, colon cancer. The article points to a study by the Dana-Farber Cancer Institute and the Harvard School of Public Health which, says the post, demonstrated that colon cancer patients who have high levels of vitamin D have a reduced risk of death compared to patients who are vitamin D deficient. This evidence suggests that vitamin D might protect against colon cancer and might help extend the life of those with colon cancer.

Bottom line: Low levels of vitamin D can be the cause of many health issues, including gut-related problems. Stay on top of your vitamin D levels by testing. Learn more here.


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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