What Vitamin and Mineral Deficiency Causes Canker Sores?

Deficiencies in vitamin B12, folate, iron, and zinc are the nutrient shortfalls most consistently linked to recurrent canker sores, with vitamin D and other B vitamins playing a supporting role. A meta-analysis found that people with recurring canker sores were roughly four times as likely to be low in vitamin B12 and over seven times as likely to be low in folate compared to people without them. But the relationship between nutrients and mouth ulcers is messier than a simple “take a supplement and they go away,” and the specific deficiency that matters varies from person to person.

Vitamin B12 Has the Strongest Individual Link

Of all the nutrients studied, vitamin B12 stands out as the one with the most consistent connection to recurrent canker sores. In a large study comparing over 500 canker-sore patients to healthy controls, B12 deficiency was significantly more common in the ulcer group, and having more than one deficiency at the same time was also more frequent among patients.¹ Research on dietary intake, rather than just blood levels, has found that people who get recurrent canker sores consume less B12 than the general population, falling about 7% below the recommended daily intake on average.² That gap might sound small, but even marginal deficiencies seem enough to tip the scales in someone already prone to ulcers.

A randomized trial tested whether supplementing B12 directly could help. Fifty-eight patients received either 1,000 mcg of sublingual B12 at bedtime or a placebo for six months. By the end of the trial, about three-quarters of the B12 group had achieved complete remission, compared to roughly a third of the placebo group. Pain, ulcer count, and the length of each outbreak all dropped, and the benefit appeared regardless of whether the patient’s blood B12 was low to begin with.³ That last detail is interesting: it suggests B12 may act on the mouth lining in a way that helps even when your overall blood levels look fine.

Folate Deficiency and Its Outsized Risk

Folate, also known as vitamin B9, had the largest odds ratio of any nutrient deficiency in the meta-analysis, with canker-sore patients roughly seven and a half times more likely to be folate-deficient than controls.⁴ Despite that striking number, the absolute percentage of patients who are actually low in folate tends to be smaller than the percentage low in B12 or iron. One study of 273 patients found folic acid deficiency in only about 2.6% of them.⁵ So the risk is high when folate is low, but folate deficiency itself is less common in the general canker-sore population.

Dietary data reinforces the link: people with recurring canker sores consumed about 20% less folate per day than matched controls, a much wider gap than the 7% shortfall seen with B12.² Both B12 and folate are essential for building and repairing cells that turn over quickly, like the cells lining your mouth. When either is scarce, the oral mucosa can become thin and fragile, setting the stage for ulcers to form more easily.

Iron and Ferritin

Iron deficiency is one of the most common nutritional shortfalls worldwide, and it shows up frequently in canker-sore patients too. In one study focused specifically on ferritin (the protein that stores iron), about two-thirds of oral ulcer patients had low ferritin values.⁶ A systematic review and meta-analysis found that iron depletion can lead to thinning of the tissue lining the mouth, making it more vulnerable to ulcer formation.⁷ The meta-analysis of hematinic deficiencies put the odds ratio for low ferritin at about 2.6, meaningful but lower than the ratios for B12 and folate.⁴

There is a gender dimension here. In the large study of 517 canker-sore patients, ferritin deficiency was far more common in women, while B12 and folate deficiencies were more common in men.¹ This makes sense given that menstruation increases iron loss. If you are a woman with recurring canker sores, iron is especially worth checking.

Zinc

Zinc is less studied than B12 or iron in the canker-sore context, but the evidence is growing. A pilot study found zinc deficiency in 28% of canker-sore patients compared to just 4% of controls, and the average serum zinc level was significantly lower in the patient group.⁸ On the treatment side, a systematic review looking at zinc supplementation for canker sores found that five out of seven studies showed significantly better outcomes with zinc, including reduced recurrence and improved symptoms.⁹

An older but notable study gave zinc sulfate to 17 patients with recurring ulcers. All nine patients who started with low zinc levels improved, seeing a 50% to 100% drop in how often they got ulcers. Among the eight patients whose zinc was normal to begin with, only three improved.¹⁰ That pattern mirrors what we see with B12: supplementation helps most when there is an actual deficiency, though some people benefit even without one.

Vitamin D

Vitamin D is a newer entrant to the canker-sore conversation, but the evidence is piling up. A study comparing canker-sore patients to controls found that patients’ average vitamin D levels were significantly lower, hovering around 11 ng/ml compared to about 16 ng/ml in healthy individuals.¹¹ Both of those numbers fall well below the 20 ng/ml threshold generally considered the cutoff for deficiency, so both groups were low, but the canker-sore patients were substantially lower.

A 2023 meta-analysis pooling data from multiple studies confirmed a significant association between low vitamin D and canker-sore risk, with patients’ levels averaging nearly 9 ng/ml lower than controls.¹² Vitamin D plays a well-known role in immune regulation, and its deficiency may allow the kind of unchecked inflammatory response that produces ulcers. There are not yet strong supplementation trials specifically targeting canker sores with vitamin D, but correcting a deficiency is sensible regardless.

The Other B Vitamins People Forget About

B12 and folate dominate the research, but B1 (thiamine), B2 (riboflavin), and B6 (pyridoxine) deserve attention too. A study of 60 patients with recurrent mouth ulcers found that about 28% were deficient in one or more of these three vitamins. When those deficient patients received replacement therapy for a month, they experienced significant and sustained improvement in their ulcers over the following three months. Patients who received the same supplements but were not deficient did not see the same benefit.¹³ The takeaway: these deficiencies are less common than B12 or iron shortfalls, but when they are present, fixing them can make a real difference.

Why a Daily Multivitamin May Not Be Enough

Given all the nutrients involved, you might assume that popping a multivitamin would solve the problem. A well-designed trial tested exactly that idea. Patients with recurring canker sores took either a daily multivitamin containing the standard recommended amounts of essential vitamins or a placebo. After monitoring them for a full year, there was no meaningful difference between the groups. The multivitamin arm averaged about 4.2 new episodes compared to 4.6 in the placebo arm, and the duration of each episode was essentially the same in both groups.¹⁴

This result seems to contradict the strong evidence for individual nutrient supplementation described above. The likely explanation is that a generic multivitamin provides standard doses spread across many nutrients, while targeted supplementation corrects a specific shortfall with a higher, therapeutic dose. If your problem is a significant B12 deficiency, the modest amount of B12 in a multivitamin may not move the needle. Likewise, if you are not deficient in anything, no amount of extra vitamins will change the underlying immune process driving the ulcers. The evidence consistently points toward identifying and correcting your particular deficiency rather than taking a broad-spectrum supplement and hoping it helps.

When the Gut Is the Real Problem

Sometimes canker sores are not caused by what you eat but by how well your body absorbs it. Celiac disease damages the lining of the small intestine, which leads to malabsorption of several nutrients at once. Recurrent canker sores are recognized as one of the oral manifestations of celiac disease, sometimes appearing before the classic digestive symptoms do.¹⁵ A person with undiagnosed celiac disease can eat a perfectly balanced diet and still develop deficiencies in B12, folate, iron, and zinc because the intestinal damage prevents proper absorption.

Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis also carry a higher rate of canker sores. In these conditions, the mouth ulcers may result from both the inflammatory disease process itself and the nutritional deficiencies caused by chronic intestinal inflammation and malabsorption.¹⁶ If you get frequent canker sores alongside digestive symptoms like bloating, diarrhea, or unexplained weight loss, the ulcers could be a signal that something deeper is going on.

Clinicians who evaluate recurring canker sores are advised to look for these underlying systemic conditions. Identifying a “correctable cause” such as a gastrointestinal disease or a hematinic deficiency can lead to treatment that resolves or substantially reduces the ulcers.¹⁷

Having Multiple Deficiencies at Once

One detail that often gets overlooked is that many canker-sore patients are not just low in one nutrient. The 517-patient study found that combination deficiencies were significantly more common in the ulcer group than in controls.¹ A separate group of 273 patients showed anemia in about 21% and iron deficiency in about 20%, with smaller but notable percentages deficient in B12 and folic acid.⁵ This clustering may explain why some patients do not respond to correcting just one deficiency: if you replenish your B12 but remain low in iron, the ulcers may persist. Comprehensive testing rather than checking a single level is more useful.

Genetics Can Affect How You Process These Nutrients

Your genes may influence whether a borderline nutrient intake tips into a functional deficiency. One area researchers have explored involves the MTHFR gene, which codes for an enzyme that processes folate in the body. One study found a significant association between a common MTHFR gene variant (C677T) and both canker-sore risk and the number of ulcers a patient developed.¹⁸ People who carry this variant are less efficient at converting dietary folate into its active form, so they may need more folate to stay above the threshold where problems begin.

The picture is not settled, though. A more recent case-control study found no significant association between the same MTHFR variants and canker-sore risk.¹⁹ Conflicting results like these are common in genetics research, where population differences and study size can swing the outcome. The practical takeaway is that genetics may partly explain why two people eating the same diet end up with very different canker-sore histories, but we cannot yet use a genetic test to predict who will benefit from extra folate.

What Happens at the Tissue Level

A proteomics study looked at saliva from canker-sore patients and found that during active ulcers, several biological pathways related to B9 and B12 metabolism were disrupted, alongside pathways involving selenium and nitrogen metabolism.²⁰ This is a different angle from the blood-test studies: it suggests that even the local chemistry inside the mouth shifts when ulcers are present, and that vitamin-related processes are part of that shift. The researchers noted that canker-sore patients generally had lower vitamin levels than controls, though the differences were not always statistically significant. It hints at a local tissue effect that might not show up clearly in a standard blood panel.

The mechanism researchers most commonly point to is that B12, folate, and iron are all critical for rapid cell turnover. The lining of your mouth replaces itself roughly every one to two weeks, which means it is constantly building new cells. When the raw materials for that construction are in short supply, the tissue becomes thinner and less resilient. Minor trauma from biting your cheek, eating something sharp, or even brushing your teeth can then trigger an ulcer that heals slowly.² Researchers have noted that changes like inflammation and glossitis in the mouth lining can be the earliest and only sign of a developing B12 or folate deficiency, appearing before the classic symptoms of anemia.

Non-Nutritional Triggers Worth Knowing About

Nutrient deficiencies are only one piece of the canker-sore puzzle. Stress, minor mouth injuries, hormonal changes, and certain ingredients in toothpaste (particularly sodium lauryl sulfate, the foaming agent) are all recognized triggers. Some people find their ulcers flare around menstrual cycles or during periods of intense stress, with no nutritional change at all. These triggers can act alone or in combination with underlying deficiencies, which is one reason canker sores can feel so unpredictable.

A practical step many people miss is switching to a toothpaste without sodium lauryl sulfate, especially if ulcers tend to appear shortly after brushing. It will not fix a nutritional deficiency, but removing a mechanical and chemical irritant can reduce how often ulcers are triggered in the first place.

What Testing Looks Like

If you get canker sores more than a few times a year, it is reasonable to ask your doctor or dentist to check a few blood levels. The typical workup includes a complete blood count to look for anemia, along with serum iron or ferritin, B12, and folate levels. Zinc and vitamin D testing can be added, especially if the first round of results comes back normal but the ulcers keep recurring. Some clinicians will also screen for celiac disease with an antibody test, since canker sores can be its earliest visible sign.

About 46% of canker-sore patients in one large study had at least one hematinic deficiency, compared to about 28% of healthy controls.¹ That means the odds are decent that bloodwork will turn up something actionable. And when it does, targeted correction of the specific deficiency is far more effective than blanket supplementation.

1
PubMed Central. Hematinic deficiencies in patients with recurrent aphthous stomatitis: variations by gender and age
2
PubMed Central. Reduced dietary intake of vitamin B12 and folate in patients with recurrent aphthous stomatitis
3
American Associates, Ben-Gurion University of the Negev. Vitamin B12 identified As An Effective Canker Sore Therapy, Study Suggests
4
British Dental Journal. Impact of haematologic deficiencies on recurrent aphthous ulceration: a meta-analysis
5
PubMed. Recurrent aphthous stomatitis – Etiology, serum autoantibodies, anemia, hematinic deficiencies, and management
6
PubMed Central. Significance of ferritin in recurrent oral ulceration
7
PubMed Central. The Relationship Between Iron and Zinc Deficiency and Aphthous Stomatitis: A Systematic Review and Meta-Analysis
8
PubMed. Zinc deficiency in patients with recurrent aphthous stomatitis: a pilot study
9
PubMed. Zinc supplementation for prevention and management of recurrent aphthous stomatitis: a systematic review
10
PubMed. Zinc sulfate supplementation for treatment of recurring oral ulcers
11
PubMed Central. Vitamin D levels in patients with recurrent aphthous stomatitis
12
PubMed Central. Vitamin D deficiency and risk of recurrent aphthous stomatitis: updated meta-analysis with trial sequential analysis
13
PubMed. Recurrent aphthous ulceration: vitamin B1, B2 and B6 status and response to replacement therapy
14
PubMed Central. Multivitamin therapy for recurrent aphthous stomatitis: A randomized, double-masked, placebo-controlled trial
15
PubMed Central. Beyond the Gut: A Systematic Review of Oral Manifestations in Celiac Disease
16
PubMed Central. Oral pathology in inflammatory bowel disease
17
PubMed. Recurrent aphthous stomatitis: clinical characteristics and associated systemic disorders
18
PubMed. Association of MTHFR gene C677T mutation with recurrent aphthous stomatitis and number of oral ulcers
19
PubMed Central. Methylenetetrahydrofolate Reductase C677T and A1298C Polymorphisms are Not Associated With Recurrent Aphthous Stomatitis: A Case-Control Study
20
Nature. Salivary proteome of aphthous stomatitis reveals the participation of vitamin metabolism, nutrients, and bacteria