vitamin D and Gut
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Vitamin D and Gut Health

Vitamin D is also called the sunshine vitamin. Just thinking about it makes me happy. The days are getting longer, but in the Netherlands, where I live, most days are still grey and moody. In northern parts of the world, the sun doesn’t show itself that much whole year-round. Luckily our body can store vitamin D after we consume (or produce!) it. What makes vitamin D so special to us to store it? Does vitamin D have a connection with inflammatory bowel disease (Crohn’s disease and Ulcerative Colitis) and Irritable Bowel Syndrome (IBS)? And what is the link between our microbiome, vitamin D and gut health? Read on to find out!

In the last couple of months I had an intern working with me in my dietetic practice, her name is Shirley Zwart, and she wrote this article for you!

What Are Vitamins?

Vitamins are nutrients that occur in small amounts in food and drinks. They are needed for normal growth and development and to stay healthy. They do not provide energy, but some vitamins do help the digestive system to obtain energy. The body can’t produce vitamins or at least create them in quantities that are high enough to meet our needs. That is why they are known as essential (indispensable) nutrients.

What is Vitamin D?

Vitamin D is a fat-soluble vitamin and is also called the sunshine vitamin. It is one of the few vitamins that the body can make itself and is actually a prohormone, or precursor of a hormone. Under the influence of sunlight, our skin creates vitamin D. Up to 80% of our vitamin D requirements need to be met through exposure to sunlight. The other 20% of our vitamin D requirement is absorbed in our gut, coming from the foods we eat which naturally contain vitamin D or that have been fortified with it.

Functions of Vitamin D

Vitamin D has several functions in our body.

Support of bone and dental health. It aids in calcium and phosphorus absorption in our intestinal tract and captures it in the skeleton and our teeth. This is needed for growth and to prevent bone loss.

Help in muscle function by maintaining a calcium balance.

Support our immune system with anti-inflammatory properties. May improve inflammatory bowel disease.

May have a role in our brain and nervous system. Vitamin D has a variety of neuroprotective roles, including helping to rid the brain of beta-amyloid, an abnormal protein that is believed to be a major cause of Alzheimer’s disease.

Where Do We Get Vitamin D From?

There are 2 forms of vitamin D: vitamin D2 (ergocalciferol, from plant sources) and vitamin D3 (cholecalciferol, from animal sources). Vitamin D is absorbed in the small intestine after consuming a meal or is being formed in the skin under the influence of Ultraviolet B (UVB) radiation, which is part of sunlight. Vitamin D2 is formed in certain mushrooms and fungi. Whereas vitamin D3 is formed in the skin of humans and animals. That is why vitamin D3 occurs naturally in foods of animal origin.

Vitamin D can be found naturally in foods including:
Oily fish; e.g. sardines, mackerel, salmon, herring, kippers, pilchards, trout and eel, cod liver oil also tends to contain a lot of vitamin D
Red meat (click to read my article on red meat)
Egg yolks

It can also be found in fortified foods like margarine, some breakfast cereals, some yogurts, milk and soy milk.

Vitamin D Deficiency

Vitamin D deficiency in children causes rickets, a condition that results in weak and soft bones. Children with rickets may develop deformities in their legs, have stunted growth, bone pain, a large forehead, and trouble sleeping.

In adults vitamin D deficiency may result in:

Osteomalacia, a bone-thinning disorder that occurs exclusively in adults and is characterized by proximal muscle weakness and bone fragility

Osteoporosis, a condition characterized by reduced bone mineral density and increased bone fragility

Muscle weakness, aches and twitches


Periodontitis, a local inflammatory bone loss that can result in tooth loss

Depression, low vitamin D levels are a risk factor for depression.

Vitamin D and Inflammatory Bowel Disease

Vitamin D deficiency is common among patients with inflammatory bowel disease (IBD). What isn’t clear is whether the deficiency is a cause or a result of the disease. Vitamin D may play a role in the development and course of IBD. Patients with IBD and vitamin D deficiency had more frequent relapses, higher postoperative recurrence, poorer quality of life and failure of response to biologics like anti-inflammatory medication. Maintaining an adequate vitamin D status may improve the relapse rate and inflammation. Further research is still needed to determine the underlying processes.

Vitamin D and Irritable Bowel Syndrome

Vitamin D deficiency is also common among patients with Irritable Bowel Syndrome (IBS). This deficiency is mostly caused by low exposition to sunlight and a diet low in vitamin D. Interestingly, both IBS patients and people with vitamin D deficiency have similar symptoms. In both cases, there is an increase in the production of pro-inflammatory markers and a reduction in the release of anti-inflammatory markers, increased permeability of the lining in the bowel, imbalance or maladaptation of the gut microbiome, and a disruption in the communication between the brain and the gut.

Our brain can influence the composition of the microbiota by, for example, adjusting the intestinal motility, secretions in the gut and intestinal permeability. The communication between the intestines and the brain is called the “gut-brain axis”. Furthermore, both IBS and vitamin D deficiency may cause symptoms of abdominal pain and distention, bloating and dissatisfaction with bowel habits and gut, increased depression, and reduction in reported quality of life.

IBS patients who supplement vitamin D see improvements in the production of pro-inflammatory markers and release of anti-inflammatory markers, normal permeability of the bowel, a balanced gut microbiome, restored brain-gut-axis, reduction in abdominal pain and distention, bloating, and dissatisfaction with bowel habits, and improved quality of life.

Vitamin D and Gut Health and the Microbiome

A recent study on the effects of UVB light on the microbiome showed an increase in different species of gut bacteria (microbiome), as soon as a week after exposing the subjects to UVB light. Some of the participants supplemented vitamin D at the start of the study and had sufficient vitamin D levels. Most of the other participants (no supplementation) didn’t have sufficient vitamin D levels. This suggests that supplementing vitamin D is an effective way to prevent vitamin D deficiency. The participants who did not supplement vitamin D also had a significant lower bacterial diversity as compared to the participants who did supplement vitamin D.

Are you suffering from IBS and has a vitamin D supplement not helped you? Schedule an online consultation at my online dietitian practice Darm diëtist, and I will help you with all your questions!

Functions of the Gut Microbiome

Our gut microbiome has several functions, and high diversity in bacteria is thought to be more resilient against stressors and is seen as a hallmark of health and healthy aging. Our microbiome:

Helps the body to digest certain foods that the stomach and small intestine have not been able to digest

Helps with the production of some vitamins (B and K)

Helps us combat pathogenic microorganisms, maintaining the wholeness of the intestinal mucosa

Plays an important role in the immune system, performing a barrier effect.

If you want to read more about gut bacteria, click here for my article on how your gut bacteria can promote obesity.

Study on UVB Light and the Microbiome

The participants in the study, only healthy females, underwent three full-body exposures within a week, in a phototherapy machine, which is a sort of specialized tanning machine. A week after exposing the participants to UVB light, their vitamin D levels increased with approximately 10%. Surprisingly, there was a significant increase in the diversity of the gut microbiome in participants who had not supplemented vitamin D prior to the study.

At the end of the study, the participants who did not supplement had increased their diversity to the same levels as the participants who were supplementing vitamin D before the study. This increase included several bacterial families that are associated with a healthy microbiome and have been associated with improved health status as compared to the microbiome of those individuals suffering from diverse immune-mediated inflammatory diseases.

Seasonal Changes in Inflammatory Bowel Disease and Irritable Bowel Syndrome

Several chronic inflammatory diseases show seasonal patterns in the severity of the disease. The relapsing and remitting nature of IBD is strongly associated with vitamin D levels. Our microbiome has seasonal fluctuations in their composition and these correspond with fluctuations in vitamin D levels throughout the year.

In earlier studies, the changes were attributed to different food availabilities and consumption between seasons and over the year. With the findings that UVB light can rapidly alter the gut microbiome without any dietary changes, the seasonal fluctuations in our microbiome might be explained by sun exposure throughout the year. While this seasonal variation of the microbiome might not have obvious effects on healthy individuals, it could be of greater importance for people with immune dysfunction.

Flare-ups in IBD and IBS symptoms are commonly reported when serum vitamin D levels are low. This study raises the question of whether these changes in disease activity could be accelerated by coexisting changes in microbiome composition, and if disease activity in IBD and IBS can be influenced by sunlight (UVB) exposure.

What Can You Do When You Suspect a Vitamin D Deficiency?

For most people, vitamin D supplementation is recommended. Getting our daily amount of sunlight is difficult. Especially when don’t come out in the sun on a daily basis, live far from the equator, have an inside job during the daytime, have your hands and/or face covered up by clothing, or if you’re living in northern parts of the world and have a dark skin tone.

People with IBD and IBS may benefit from daily vitamin D supplementation and especially when sunlight is not plentiful. Not only does vitamin D supplementation reduce the risk of vitamin D deficiency it also may reduce the risk of flares, help restore the bowel and the diversity of the microbiome and increase your quality of life!

If you want to be sure about your vitamin D status, request a blood test at your general practitioner.

How Much Vitamin D Must My Supplement Contain?

To determine how much vitamin D your supplement should contain, you can look at the table with recommended daily allowances established by the Food and Nutrition Board (FNB) from the Institute of Medicine, Washington DC. These numbers represent a daily intake that is sufficient to maintain bone health and normal calcium metabolism in healthy people. Do not exceed these amounts, unless on the prescription of your GP.

Recommended Dietary Allowance (RDA) for Vitamin D
Age Male Female Pregnancy Lactation
0–12 months (adequate intake) 10 mcg 10 mcg    
1–13 years 15 mcg 15 mcg    
14–18 years 15 mcg 15 mcg 15 mcg 15 mcg
19–50 years 15 mcg 15 mcg 15 mcg 15 mcg
51–70 years 15 mcg 15 mcg    
>70 years 20 mcg 20 mcg    

RDA: Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.

Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.

When looking at vitamin D supplements, the dosage is normally described as IU. 400 IU is 10 mcg. Vitamin D is very affordable and is absorbed best when it’s in a soft gel with oil. For example the 365 Everyday Value, Vitamin D3 400 IU, 100 ct from Amazon.

Vitamin D Supplement

Have you been taking vitamin D supplements? Have you noticed a change in your gut symptoms and seen the link between vitamin D and gut health? Let me know your story!

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  1. Hello Manon. I live in the Tropics, but recently we’ve been having overcast, chilly weather. I have been noticing persons having flare-ups in their hemorrhoids and increased demand for intestinal worm treatment. Incidentally, both conditions (hemorrhoids and intestinal worm infestation) have a similar “itchy bottom” symptom. Perhaps, this gut-sunshine-vitamin-d connection might be playing a role in this occurrence (?).

    Keep up the good (and brave) work.

    1. Hey Andre,

      I’m afraid I can’t say anything about that connection. But if it’s only been recently that is has been less sunny, I wouldn’t expect a vitamin D deficiency to occur yet.
      Vitamin D is a fat-soluble vitamin and we can store this in our fat reserves.
      It takes a longer period of time to get a deficiency.

      But if someone talks to you about it, you can always tell them to have their vitamin D levels tested!

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