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Do you want to start feeling better?

Yes, Where Do I Start?

4 Important Gut-Health Vitamins You May Lack

These Crucial Vitamins Are Commonly Missing From the American Diet

Key Takeaways:
  • Most Americans aren’t getting enough of four crucial vitamins for gut health.
  • Food is the ideal way to get most of the vitamins you need for gut health, but vitamin D is an exception. Here, sunlight and supplements come into play.
  • As your gut gets stronger and healthier, it will help you to better absorb all micronutrients, including vitamins.

Eating a healthy diet, taking probiotics, and avoiding foods that trigger inflammation are all proven ways to keep your gut happy and healthy.

In addition, some specific vitamins play an important role in the gut. When optimizing digestive system function and gut microbiome health, it’s helpful to know what these vitamins are and how to get enough of them.

In this article, we’ll take a close look at some essential vitamins for digestive health, including recommended amounts and whether testing for vitamin levels is worthwhile.

But before we get into the details, let’s take a broader brushstroke view of how vitamins support gut health. 

Important Vitamins for Gut Health

A well-functioning gut is essential for vitamins to be properly absorbed. However, the relationship also works the other way around: The gut and its microbiota also need vitamins to function well [1]

The research on this bi-directional gut-vitamin relationship is still preliminary. However, vitamins seem to modulate gastrointestinal health by adjusting the composition and function of the gut microbiome and supporting the healthy functioning of the gut barrier and immune system [1].

At a mechanistic level, some vitamins (water-soluble ones like vitamin C and B vitamins) serve as cofactors to make enzymes in the body work well [1]. Other vitamins (the fat-soluble ones like vitamins A, E, D, and K) form important parts of cell walls [1]. 

These vitamins may also support gut health by improving the diversity of microbes and their pro-gut functions; boosting immune function; and reducing free radical damage [1].  The following table summarizes research showing the potential mechanisms by which healthy levels of vitamins may support gut health [1].

Beneficial Effects on Gut HealthVit AB VitsVit CVit DVit EVit K
Optimizing microbial interactions, metabolism, and signaling within the gut microbiome
Reducing free radical damage✔ (B2)
Increasing microbial diversity✔ (B2, B3)
Increasing production of short-chain fatty acids (SCFA)
Increasing beneficial microbes✔ (B2)
Improving gut barrier function
Optimizing immune function

Vitamin Deficiency Versus Inadequacy

Vitamin deficiencies (severe) are uncommon in the U.S., but vitamin inadequacies (less severe) are quite common. 

True vitamin deficiencies cause specific diseases; for example, a complete lack of vitamin C causes scurvy.

By comparison, vitamin inadequacies don’t result in acute conditions, but they may contribute to more gradual-onset problems like fatigue, lower immunity, cognitive difficulties, and chronic diseases like cancer, heart disease, and type-2 diabetes [2].

Vitamin inadequacy largely results from people eating a Westernized, high-calorie, nutrient-poor diet that lacks fruits, veggies, whole grains, and dairy products [2, 3].

When it comes to the six gut-supporting vitamins listed in the table above, four are commonly inadequate in the U.S. diet and thus the focus of this article. They are [4]:

  • Vitamin A: 42% of people in the U.S. have inadequate intake
  • Vitamin C: 44% have inadequate intake
  • Vitamin E: 74% have inadequate intake
  • Vitamin D: 96% have inadequate intake

Your intake of these vitamins counts as inadequate if you consume less than the Estimated Average Requirement, or EAR.

The EAR is the nutrient intake that’s estimated to meet the requirements of half the healthy individuals in a particular life stage and gender group.

Getting Your Gut Vitamins: Focus on 4

Eating a vitamin-rich diet (or supplementing where appropriate) is the best way to make sure vitamin deficiencies aren’t compromising your gut health or adding to any gut symptoms you might be experiencing now.

Let’s look in detail at the four vitamins that are both important to gut health and commonly found to be inadequate in U.S. diets.

Vitamin A

In the gut, vitamin A is necessary for maintaining a healthy intestinal barrier, suggesting that low vitamin A status could contribute to a leaky gut and subsequent dysbiosis. Studies—mostly observational, with a couple of clinical trials [5, 6]—have found that vitamin A can also change the composition of the gut microbiota, reduce diarrhea, and reduce the prevalence of norovirus [1]. 

Dietary Sources

Dietary vitamin A comes as retinol (the active form) from animal foods and carotenoids (which get converted to active vitamin A after absorption) from fruits and veggies [1]. 

You’ll almost certainly get enough total vitamin A by including the following in your diet often [7]:

  • Oily fishes, such as herring and salmon
  • Beef liver and other organ meats 
  • Green leafy vegetables
  • Other colorful orange and yellow vegetables, such as sweet potatoes, carrots, broccoli, and winter squash
  • Orange fruits, including cantaloupe, mangos, and apricots
  • Dairy products, such as milk and cheese
  • Eggs

How Much Vitamin A Do You Need?

Women need 700 micrograms (about 2,300 IUs) per day [8]. Men need 900 micrograms (3,000 IUs) per day [8]. Pregnant adults need 770 mcg, and breastfeeding adults need 1,300 mcg per day [9].

Is Testing Helpful?

No. Blood testing is an option for confirming a vitamin A deficiency (when your blood levels are less than 20 mcg/deciliter), but it may not reflect the actual vitamin A concentration in the body [10]. It’s easier to just make sure you consume enough vitamin A on a daily or weekly basis. 

Vitamin C

We don’t know too much about vitamin C’s direct impact on the gut microbiome per se, but cell studies have found that this vitamin has antimicrobial activity against bacteria, viruses, and fungi [1]. 

One recent study found that levels of short-chain fatty acids (which promote a healthy gut) rose after researchers delivered vitamin C directly to the colon [11]. Vitamin C might also reduce the level of free radicals (which cause oxidation and inflammation) in the gut lining and help the body fight against H. pylori infections in the stomach [1].

Dietary Sources 

It’s relatively easy to achieve an adequate vitamin C intake if you increase your intake of fruits and vegetables. Some of the best sources include [12]:

  • Citrus fruits (such as oranges and grapefruit) and their juices 
  • Red and green bell peppers 
  • Kiwifruit

Other fruits and vegetables, such as broccoli, strawberries, cantaloupe, baked potatoes, and tomatoes, also have vitamin C. And if you like liver and kidneys, they’re rich in it, too [8].

How Much Vitamin C Do You Need?

The daily recommended intake is 75 mg for women and 90 mg for men [8]. Pregnant adults should up their vitamin C to 85 mg [12]. Breastfeeding increases your requirement to 120 mg, and smokers need a higher intake, too [12]. 

Is Testing Helpful?

No. Blood tests aren’t great for diagnosing a chronic vitamin C deficiency (less than 0.2 mg/deciliter in plasma). Plus, it’s super easy to get enough vitamin C if you improve your diet. Most people will also respond quickly to vitamin C supplementation [13].

Vitamin E

Vitamin E is a fat-soluble antioxidant, which helps repair cell membranes to keep them healthy [1].

Several human studies have suggested that vitamin E has the potential to shape the gut microbiome [14], though the specifics of this are unclear [1]. With its antioxidant capabilities, vitamin E may theoretically help combat free radical damage in the gut and help maintain the integrity of the gut wall [1].

In addition to its potential benefits for the microbiome, vitamin E is an important nutrient for the entire body [4]. 

Dietary Sources

The richest sources of vitamin E are foods that contain unsaturated fats, so low-fat diets may not meet your vitamin E needs. Most people will be able to get enough if they eat nuts or vegetable oils daily, especially as [15]:

  • Hazelnuts, almonds, peanuts, or sunflower seeds
  • Wheat germ oil, sunflower oil, or safflower oil

Leafy greens, including spinach and broccoli, also provide some vitamin E [8]. 

How Much Vitamin E Do You Need?

The daily recommended intake for adults is 15 mg [8]. That’s true even if you’re pregnant, but if you’re breastfeeding, increase it to 19 mg per day [15].

Is Testing Helpful?

No. Proper Vitamin E deficiency (less than 0.5 mg/deciliter) is rare. Testing has little to offer unless you have [16]:

  • Genetic mutations that limit your ability to absorb or make use of vitamin E; or 
  • Fat malabsorption issues caused by conditions like cystic fibrosis or chronic pancreatitis.

Vitamin D

Early evidence suggests that vitamin D from sunshine may have a role in regulating gut microbiota [17, 18, 19]. There also appears to be an association between supplemental vitamin D and changes in the gut microbiota, but those changes haven’t been consistent across studies [11, 20, 21]. 

Overall, the evidence on vitamin D and gut health is mixed. For example, a recent meta-analysis showed that vitamin D supplements probably won’t improve irritable bowel syndrome symptoms unless your vitamin D levels are quite low (less than 20 ng/mL) [22]. 

Meanwhile, a systematic review was unable to tease out much detail on how vitamin D impacts inflammatory bowel disease (IBD) patients, but it did suggest that taking the vitamin might correlate with fewer relapses [23]. 

Dietary Sources

Vitamin D is one of the few vitamins that it’s tough to get enough of from diet alone. Typically, adequate sunshine is the best way to keep your levels right, and vitamin D from the diet is more of a complement. Nonetheless, here are some of the best dietary sources—keep in mind that you’d need to eat a lot of them daily to meet your needs [24]:

  • Fatty fish (like trout, salmon, tuna, and mackerel) and fish liver oil
  • Fortified milk (almost all of the U.S. milk supply is fortified with about 3 mcg [120 IU] vitamin D per cup, and many plant-based alternatives are similarly fortified

Mushrooms also provide a little vitamin D, especially if they have been exposed to ultraviolet light, which increases their vitamin D content [24]. Additionally, beef liver, egg yolks, and cheese have small amounts of vitamin D [24].

How Much Do You Need?

Generally, 10–15 mcg (400–600 IU) of vitamin D is the daily recommended intake in adults [8], including if you are pregnant or breastfeeding [24]. Older adults (over 70) need more (20 mcg or 800 IU) [24]. 

Vitamin D is unusual in that you don’t need dietary sources if you expose your skin to some daily sun. In fact, evidence suggests that regular, healthy (non-burning) doses of sunshine is the optimal way to get most of our vitamin D requirements [25]. Specifically, vitamin D from the sun may be better for the gut microbiome than supplemental vitamin D [11, 17, 18, 19, 20, 21].

The amount of sun exposure that will optimize your vitamin D levels varies depending on your current blood vitamin D, your skin color, and how much sunshine there is where you live [26].

However, as a rough guide, people with darker skin (phototype V) need about 25–40 minutes of middle-of-the-day sun exposure without sunscreen on 35% of the skin. This means your face, forearms, and lower legs must be exposed [27]. 

Until we have research directly calculating the amount of sun exposure people with the darkest skin (phototype VI) need to maintain adequate levels of vitamin D [28], it may be safest for VI phototypes to follow the recommendations for phototype-V skin, get your vitamin D levels checked periodically, and adjust your sun exposure if you need more. 

For lighter-skinned people (phototypes I–IV), this can be reduced to 9 minutes of daily sunlight around noon from March to September (or 13 minutes daily from June to August) [29].

Given that food sources of vitamin D aren’t as plentiful or effective for maintaining adequate levels, you should aim for healthy sun exposure as much as possible. 

In reality, though, we can’t always get as much sun as we need every day. Not only can time limitations be an issue, but clouds, smog, and older age also reduce the amount of vitamin D your skin makes [24]. This means that supplements are sometimes the only reliable way to get sufficient vitamin D, especially in less sunny climates and times of year [30].

Is Testing Helpful?

Yes. Testing for vitamin D once or twice a year is worth it because low levels are so common, and testing is not too expensive (usually less than $50). You typically get an accurate result that can inform whether you need to supplement and how much to take. Note that if you have active liver or kidney disease, you may need more frequent testing—please work with your doctor on this [31].

What Dosage of Vitamin D Supplement?

I usually recommend that my patients try to keep their vitamin D blood levels at 100–125 nmol/L (40–50 ng/mL). This is a bit higher than the standard recommendation of 75 nmol/L (30 ng/mL), but in my experience, this higher level is more beneficial for most people.

When you get your blood vitamin D levels tested regularly, you can select your D dosage according to the following recommendations: 

If your vitamin D level is…Consider taking this amount of vitamin D:
Close to sufficient (75–100 nmol/L or 30–40 ng/mL) 400 IU per day [8, 32], and test your vitamin D levels again in 6 months (ideally in winter) to see how they’ve changed from baseline 
Insufficient (25–75 nmol/L or 10–30 ng/mL)1,000 IU/day [33]
Clearly deficient (less than 25 nmol/L or 10 ng/mL) 1,000–2,000 IU/day [33]

With regular testing, you can tweak your daily supplement intake up or down, depending on your test results.

Choose vitamin D3 over D2 for best absorption and utilization by the body [34]. 

Is a Multivitamin a Good Idea for Gut Health?

Eating a whole-food diet is generally the best way to meet your nutrient needs. And if your digestive tract is having a hard time absorbing nutrients, you’ll be better off healing your gut and eating a nutritious diet than relying on vitamin supplements for the long haul.

That said, I will recommend temporary multivitamins to my patients when they have a gastrointestinal condition they are working on healing [35]. Taking an A–Z multi-micronutrient formula comes with a few downsides but offers sensible nutritional insurance when your digestion is compromised or your diet and food choices are limited [36, 37, 38, 39, 40]. 

Indeed, multivitamins can provide adequate nutrients when you need them, except for potassium (which is generally very low in multivitamins) and fiber [41]. However, you may not need some of the nutrients they contain and run the risk of exceeding the upper limits for vitamins [38, 39, 40]. This is when calculating your general vitamin intake from food can be helpful, so you can see if you should skip the multi and just go for individual vitamins.

I might recommend individual vitamins (like vitamin D) for several reasons: 

  1. You take a prescription medication that depletes your nutrient levels, and your doctor has asked you to supplement those single nutrients [35, 38, 39, 40].
  2. You eat well but you have osteoporosis and need more calcium, or you have iron deficiency anemia and need more iron (63) [38, 39, 40].
  3. You’re looking to target a specific nutrient inadequacy, and the multivitamin you’re taking doesn’t provide a high enough dose. 
  4. Your diet is low in just one or two nutrients and a multi would give you too much of the other nutrients and be a waste of money.
  5. Your diet is plant-based, which means you don’t get enough vitamin B12, the most bioavailable type of which occurs in animal-based foods.

Diet Is the Best Way to Improve Gut Health 

Before signing off on the topic of vitamins for gut health, let’s step back a little and focus briefly on diet. Dietary change is so fundamental to overall gut health that it should always come first, ahead of any supplement.

For many people, a Mediterranean diet is a good option for increasing micronutrient (vitamin and mineral) intake [42]. It is also a microbiome-friendly diet [43] and has healthy heart benefits [44].

However, any diet that minimizes processed food is a step in the right direction. Just be aware of any foods that trigger symptoms for you while you progress through a gut-healing journey.

Many of my patients find that a Paleo-style diet is a healthy, whole-food diet that gives them solid nutrition while minimizing gut symptoms.

If your gut issues are more significant—particularly if higher-carbohydrate foods like fruits, bread, and vegetables seem to trigger your symptoms—a low-FODMAP diet may be more helpful. 

Probiotics Are the Most Important Gut Health Supplement

Before upping their vitamin intake, I recommend that my patients start with probiotics, and for good reason. Not only do probiotics improve digestive symptoms, they can improve your ability to absorb nutrients, including those gut-supporting vitamins.

When my patients have digestive symptoms, multi-species probiotics are the first supplements I recommend. Of course, probiotics can treat IBS symptoms, such as gas, bloating, abdominal pain, diarrhea, and constipation, with very few (if any) side effects [45, 46, 47, 48, 49, 50, 51].

But when you take probiotics, you also work on correcting any microbial dysbiosis, leakiness, and inflammation in the gut. In turn, this can improve your ability to absorb vitamins and minerals from your diet, reducing your need for vitamin supplements [52, 53, 54].

Here are some findings from research on how probiotic supplements may improve nutritional status:

  • One meta-analysis showed that probiotics increased iron absorption to a medium-large degree [52].
  • Two randomized controlled trials showed that synbiotics—a combo of probiotics and prebiotics (fibers that feed beneficial bacteria)—improved micronutrient absorption [53, 54].
  • One systematic review of clinical trials showed that probiotics improved the absorption of vitamins B12 [55] and B9 (folate) [55]. 
  • A number of clinical studies have shown that probiotics may also enhance the absorption of calcium [55, 56, 57] and zinc [55].

In addition to all this, the beneficial bacteria in a healthy gut can actually make B vitamins and vitamin K, which may improve overall nutrient status [1, 58, 59, 60].

Glutamine and Hydrochloric Acid for Gut Health

Though they aren’t vitamins, L-glutamine and hydrochloric acid are worth a mention while on the topic of supplements that can support gut health and nutrient absorption. 

Glutamine is an amino acid that the body produces, but extreme stress and physical exercise can deplete its levels [61, 62]. This may impact the integrity of the gut because glutamine appears to keep the tight junctions within the gut wall knitted together [63, 64]. Such integrity of the gut wall is important for nutrient absorption [65].

Glutamine supplements have been found to help improve gut wall integrity in several groups of people, including: 

  • Patients with leaky gut and diarrhea-predominant IBS (in whom gut symptoms improved considerably, too) [66]
  • Recreational male athletes (sadly, women weren’t part of this study) exercising hard in hot conditions [67
  • Patients with Crohn’s disease [68

Taking an L-glutamine supplement is one option to support your gut. As for food sources, bone broth is a less potent source of L-glutamine, but it has other beneficial amino acids and minerals that can support the gut lining.

When it comes to HCl, not having enough can hinder nutrient absorption. Normally, the stomach makes enough HCl, or hydrochloric acid, when the brain signals that you’re about to eat. HCl breaks down protein, increases nutrient absorption, enhances digestion in the small intestine, and defends against pathogens. 

But in some cases, the stomach doesn’t make enough HCl. It’s worth trying HCl (as betaine HCl) if you have worked through other natural gut-healing treatments (like diet and lifestyle changes, probiotics, and antimicrobials), but stubborn symptoms such as reflux, heartburn, or bloating remain.

Studies on supplementing with betaine HCl are scarce but do show that supplementing will make the stomach more acidic, which may improve digestion and absorption [69].

The good thing about HCl is that you’ll know within a couple of weeks if it suits you. To determine whether HCl is right for you, this video might help.

Vitamins For Gut Health: Let’s Summarize

If your gut is healthy and you eat a varied, whole-food diet, you’ll likely be getting all or most of your vitamins for gut health, with the exception of Vitamin D. 

It’s pretty easy to get enough gut-friendly B vitamins and vitamin K, and a nutritious diet should get you the vitamins A, C, and E (and a little of the D) your gut desires. Adequate sunshine will get you the farthest in terms of vitamin D, but supplements are there if you need them.

If your gut needs a boost, vitamin supplements can be your temporary friends. I’m on board with my patients taking a high-quality A–Z multivitamin while they journey through gut health improvements with the help of diet, probiotics, and possibly some glutamine or HCl. And if additional vitamins or minerals are needed, singular forms can be helpful.

Typically, as your gut becomes stronger and healthier, you’ll absorb the micronutrients from food more effectively, and your need for extra vitamins will likely lessen.

If you are looking for a comprehensive plan to improve gut health, you’ll find a step-by-step guide in my book, Healthy Gut, Healthy You. Or, for more complex gut health problems, you can make an appointment with one of our experienced health practitioners.

The Ruscio Institute has developed a range of high-quality formulations to help our patients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you.

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