Most people know that we get vitamins from food. What’s often forgotten, though, is that a healthy gut microbiome also makes vitamins for us, every single day. When the balance of bacteria in the gut is disturbed (a state known as dysbiosis), this natural vitamin production falters, leaving us with hidden deficiencies even when our diet looks perfectly good on paper.
Let’s explore how the gut contributes to vitamin production, why this process is so vital, and what happens when dysbiosis gets in the way.
Your Gut: A Built-In Vitamin Factory
Inside your intestines live trillions of bacteria that play an active role in your nutrition. Some species break down fibre and resistant starch to produce short-chain fatty acids (SCFAs), which nourish the gut lining and support metabolism. Others are directly involved in vitamin synthesis, essentially turning your gut into a mini-factory for essential nutrients.
The most important vitamins produced by beneficial gut microbes include:
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Vitamin K2 (menaquinone): Produced by bacteria such as Bacillus subtilis and Lactococcus lactis. K2 activates proteins that move calcium into bones and teeth and out of soft tissues, such as arteries.
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B vitamins: Many strains of Bifidobacteria and Lactobacilli make a range of B vitamins, including B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate) and B12 (cobalamin).
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Vitamin C (in very small amounts): Certain gut species have been shown to synthesise ascorbic acid locally, helping to protect intestinal tissues from oxidative stress.
These bacteria-created vitamins aren’t just produced and forgotten, they’re absorbed through the intestinal lining, supplementing what we eat. In a balanced microbiome, this microbial contribution can make a meaningful difference to our nutrient status, especially for vitamins that are fragile or poorly absorbed from food.
When Dysbiosis Interrupts Vitamin Production
Dysbiosis happens when harmful or opportunistic bacteria outnumber beneficial species. This can be caused by:
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Antibiotic use
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A diet low in traditional, fermented, and fibre-rich foods
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Chronic stress
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Processed, modern diets high in refined carbohydrates and vegetable oils
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Infections, inflammation, or low stomach acid
When this microbial balance shifts, vitamin-producing bacteria are often the first to disappear. The result? Your internal “vitamin factory” slows or stops altogether.
Here’s what that can look like in the body:
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Low B vitamins: Fatigue, poor mood, weak digestion, poor skin, and nerve function issues.
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Low vitamin K2: Mineral imbalances, poor bone strength, and calcium deposits in soft tissues.
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Low biotin and folate: Hair loss, brittle nails, sluggish liver detoxification, and reduced fertility.
Even a nutrient-dense diet can’t fully compensate if the gut is no longer supporting absorption or production.
The Connection Between Gut Flora and Vitamin Absorption
The gut doesn’t just produce vitamins; it also helps the body absorb them. Beneficial bacteria keep the intestinal lining healthy and reduce inflammation, ensuring nutrients cross the gut wall efficiently.
When dysbiosis sets in, inflammation and permeability increase, meaning even if your meal is rich in vitamins, they might not reach your bloodstream effectively.
For example:
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Dysbiosis can reduce intrinsic factor and stomach acid, both needed for B12 absorption.
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Pathogenic bacteria can “steal” iron and B vitamins for their own use.
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Inflammation from gut imbalance can block vitamin D receptor activity, further contributing to deficiency symptoms.
Traditional Diets and the Gut-Vitamin Relationship
Traditional cultures, the ones studied by Dr Weston A. Price, naturally supported vitamin-producing gut flora without even knowing it. Their diets included:
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Raw and fermented foods (sauerkraut, kefir, yoghurt, raw cheeses, fermented grains and vegetables) full of living bacteria that replenish the microbiome.
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Animal fats rich in fat-soluble vitamins and natural probiotics (butter, cod liver oil, unprocessed dairy, liver pâté).
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Gelatinous broths and organ meats, which feed the gut lining and provide the raw materials for bacterial growth.
Modern diets, on the other hand, rely heavily on sterile, processed, and pasteurised foods that no longer contain beneficial microbes. Combine that with antibiotics, stress, and sugar, and the microbiome’s ability to make vitamins is severely compromised.
Signs Your Gut May Not Be Making Enough Vitamins
If you’re experiencing several of the following, it might suggest gut-driven deficiencies rather than dietary lack:
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Constant fatigue or low energy
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Mood swings, anxiety, or low motivation
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Brittle nails, thinning hair, or dull skin
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Bleeding gums or easy bruising
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Muscle weakness or cramping
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Digestive discomfort after eating
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Cravings for sugar or refined carbs
These symptoms are often subtle at first, but over time, they reflect deeper nutrient imbalances caused by poor microbial diversity.
How to Support Your Gut’s Vitamin Production Naturally
You can restore your gut’s ability to make and absorb vitamins through a traditional nutrient-dense approach:
Reintroduce fermented foods daily: sauerkraut, kefir, yoghurt, beet kvass, fermented garlic or onions, fermented turnips, or Middle Eastern-style laban and torshi.
Eat mineral- and vitamin-rich animal foods: liver, heart, kidneys, pastured egg yolks, shellfish, butter, and cod liver oil.
Include bone broths and gelatine to repair the gut lining and feed beneficial flora.
Avoid processed foods, refined sugar, and industrial seed oils, which feed pathogenic bacteria.
Stay hydrated with mineral-rich water or homemade whey drinks.
Rest and manage stress, as cortisol directly suppresses beneficial bacteria.
As balance returns, the body gradually resumes its natural vitamin-making rhythm, helping correct deficiencies from within.
In Summary
Your gut isn’t just a place where food is digested; it’s an entire ecosystem that contributes directly to your nutrition. Beneficial bacteria act like tiny nutrient factories, producing and supporting the absorption of key vitamins your body depends on.
When dysbiosis interferes, even a perfect diet can fall short. But by returning to traditional, living, and nutrient-dense foods, the kind our ancestors thrived on, we can restore this lost partnership between our gut microbes and our own health.
References
Magnúsdóttir, S., Heinken, A., Kutt, L., et al. (2015). Systematic genome assessment of B-vitamin biosynthesis suggests co-operation among gut microbes. Frontiers in Genetics, 6, 148.
Tomasetti, C., et al. (2022). Vitamin B-12 and the Gastrointestinal Microbiome: A Systematic Review. Advances in Nutrition, 13(5), 1743–1757.
Akimbekov, N., Digel, I., Sherelkhan, D., et al. (2020). Vitamin D and the Host-Gut Microbiome: A Brief Overview. Acta Histochemica et Cytochemica, 53(3), 33-42.
Li, Z., Chen, C., Yu, W., et al. (2023). Colitis-Mediated Dysbiosis of the Intestinal Flora and Impaired Vitamin A Absorption Reduce Ovarian Function in Mice. Nutrients, 15(11), 2425.
Nuraly, S., et al. (2024). The Role of Gut Microbiota Metabolites in Gut Health and Vitamin Biosynthesis. Regenerative Medicine Reports, 4(1), e3.
Zhang, Y., et al. (2025). Causal Links Between Gut Microbiota and Vitamin Deficiencies: Evidence from Mendelian Randomization Analysis. Current Medical Science.
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Disclaimer: The content of this blog post is for informational purposes only and is not intended as medical advice. While I strive to provide accurate, well-researched, and up-to-date information, I am not a licensed medical professional. The insights shared here are based on personal research and experience. I encourage you to conduct your own research and consult a qualified healthcare provider before making any health-related decisions. Your well-being is important, and any actions taken based on the information in this blog are solely at your own discretion and risk.