Vegan dietitians have typically recommended the cyanocobalamin form of vitamin B12 for vegans; it’s well-studied, stable, and inexpensive. The coenzyme forms, methylcobalamin and adenosylcobalamin, have been heavily marketed but poorly studied, with typical recommendations of 1,000 µg/day based more on caution than evidence.

A 2026 randomized trial (MATCOBIND) from India and Nepal offers the best evidence yet on methylcobalamin dosing. In 531 predominantly vegetarian pregnant women with low B12 status, both 250 µg/day and 50 µg/day of a methylcobalamin-only supplement substantially increased holotranscobalamin, the active form of B12. The 50 µg/day group reached a mean holotranscobalamin of 65.3 pmol/L, well within healthy range. This suggests that 50 µg/day of methylcobalamin as a stand-alone supplement is likely adequate for most people, though MMA was not measured (Nagpal, 2026).

There’s reason for caution about methylcobalamin in multivitamins. A stability study found that in solution, methylcobalamin degrades substantially in the presence of vitamin C, thiamin, and niacin, all common multivitamin ingredients, with losses of 48-76%. Sorbitol added as a stabilizer significantly reduced these losses, so a multivitamin containing sorbitol may be more reliable (Hadinata Lie, 2020).

More info at Coenzyme Supplements: Methylcobalamin and Adenosylcobalamin.

References

Nagpal J, Mathur M, Rawat S, et al. Maternal supplementation of vitamin B12 in predominantly vegetarian pregnant women improves their vitamin B12 status and the neurodevelopment of their infants: the MATCOBIND multicentric double-blind randomised control trial. BMJ Paediatr Open. 2026 Mar 18;10(1):e004112.

Hadinata Lie A, V Chandra-Hioe M, Arcot J.Hadinata Lie A, V Chandra-Hioe M, Arcot J. Sorbitol enhances the physicochemical stability of B12 vitamers. Int J Vitam Nutr Res. 2020 Oct;90(5-6):439-447.

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For some time, there have been concerns that supplementing with either B12 or folic acid (the synthetic version of folate) may raise blood levels high enough to increase cancer risk. These concerns are somewhat related because I recommend multivitamins as an option for obtaining vitamin B12 for vegans, and most multivitamins contain folic acid, typically 400 µg.

Because vegans don’t get enough vitamin B12 from food, unless they regularly eat significant amounts of B12-fortified foods, we usually recommend that vegans take supplements in doses much higher than the RDA. The high doses make up for the infrequency with which they’re taken; often just a few times a week rather than with every meal.

Due to the concerns about cancer, I recently completed two literature reviews of the potential negative health impacts of taking vitamin B12 or folic acid. These reviews resulted in one change to our recommendations. Because the Institute of Medicine hasn’t set an upper limit for vitamin B12, and people would ask us how much is safe to take, we recommended that people not take more than 1,000 µg per day, which we explicitly stated was arbitrary. Upon completing these reviews, I now recommend that people not exceed the upper range of VeganHealth.org’s recommended doses.

Recent advances in AI have transformed how I’m able to research these topics. I used AI to search the literature and read papers far faster than I could alone, but the analysis, judgment calls, and writing reflect over 100 hours of my own work.

Below are the summaries. If you click through to the full article, you can see different levels of detail depending on whether you read only the introduction, the rest of the text, or the tables of the study details.

Folic Acid: Does It Make a Multivitamin Unsafe?

Having reviewed the evidence, I don’t think healthy adults need to avoid multivitamins containing folic acid at the typical dose of 400 µg/day.

Folic acid is the synthetic form of folate (vitamin B9) used in fortified foods and supplements. It can prevent neural tube defects, which are serious birth defects of the brain and spinal cord. Because the neural tube closes just 28 days after conception, often before someone knows they’re pregnant, adequate folic acid intake before and in the earliest weeks of pregnancy is critical. Women of childbearing age who don’t regularly eat fortified foods like bread, pasta, and rice are at risk of inadequate intake.

Some practitioners advise avoiding multivitamins that contain folic acid due to concerns about cancer. Almost all standard multivitamins contain folic acid, so this isn’t a trivial recommendation.

The European Food Safety Authority (2023), in a comprehensive review, set the upper intake level for folic acid at 1,000 µg per day. This limit was established not because cancer risk begins at that level, but to prevent folic acid from masking the early signs of vitamin B12 deficiency, a separate and well-characterized concern. The standard multivitamin dose of 400 µg is well below this threshold.

On cancer specifically, the evidence is mixed, voluminous, and difficult to summarize. Randomized trials and large prospective studies generally show no increased risk of cancer from folic acid intakes, including supplements at typical doses. Some studies find elevated risk with high blood folate levels, but these are difficult to interpret because people with undetected cancer may already have altered folate metabolism, making it look as though high folate caused the cancer when the reverse may be true. The EFSA concluded the evidence was insufficient to establish a causal relationship between folic acid intake and cancer risk at or below 1,000 µg per day.

For a healthy adult, a standard multivitamin containing 400 µg of folic acid appears safe based on the current evidence, and for women who could become pregnant, it may be important.

For the full review, see Folic Acid: Does It Make a Multivitamin Unsafe?

B12 Supplement Safety

Elevated vitamin B12 levels in the blood are usually a sign of an underlying health problem, not a cause of one. Liver disease, kidney disease, and various cancers can all raise B12 levels, which is why studies finding associations between high B12 and poor health outcomes are generally measuring the effect of these diseases on B12 levels, not vice versa.

For vegans who supplement with B12, the evidence is cautiously reassuring. The only large study of healthy adults examining B12 supplement safety found no association between B12 supplementation and increased mortality at any dose, including 1,000 µg/day or more.

There’s one area of genuine uncertainty: Some evidence suggests that very high circulating B12 levels may modestly increase lung cancer risk. The absolute risk is small; roughly 1 in 2,000 people with high B12 levels would develop one additional lung cancer case over six years, and the evidence isn’t conclusive. This isn’t a reason to stop supplementing, but rather to stick to recommended doses rather than taking more than needed. VeganHealth’s recommended supplemental doses result in roughly half of the total B12 absorbed compared to our estimated absorption for the high-risk group in that study.

People with kidney disease should avoid high-dose cyanocobalamin supplements specifically, as there is evidence it may accelerate kidney function decline. Methylcobalamin is a better option for this group.

Supplement with B12 at recommended doses, don’t take more than you need, and don’t be alarmed by studies linking high blood B12 to disease.

For the full review, see B12 Supplement Safety.

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In light of a recent meta-analysis in which vegans had a higher risk of rectal cancer, we reinforced our recommendation that vegans should aim to meet the RDA for calcium; see Cancer Meta-Analysis (Another One!). To ensure this guidance was well-founded, I reviewed the strength of the evidence connecting higher calcium intakes to reduced colorectal cancer risk. Here’s the summary:

Higher calcium intake — ideally around 1,000 mg/day — is consistently associated with lower colorectal cancer risk in observational studies, and the World Cancer Research Fund rates the evidence for causality as “probable.” Randomized trials have been largely disappointing, however, possibly because they’re too short to capture a process that unfolds over decades or because participants already have adequate calcium intakes at baseline. For vegans, who often fall below 700 mg/day, aiming for closer to 1,000 mg/day is worth prioritizing for bone health and could also protect against colorectal cancer.

See the details in Calcium and Colorectal Cancer.

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As promised in my March 6 post, Cancer Meta-Analysis, I conducted a literature review of long-chain omega-3s (EPA and DHA) and colorectal cancer. Here’s my summary:

Given these findings, I don’t see a reason to recommend long-chain omega-3 supplements for vegans in order to prevent colorectal cancer. More details are in the article, Omega-3s and Colorectal Cancer.

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I made a quick update to the Infants section of Pregnancy, Infants, and Children:

A study of over 1.2 million infants, including 3,338 vegans, found normal growth among the vegan infants (Avital, 2026, Israel). Vegan babies were on average about 100 grams (3.5 oz) lighter at birth (3.2 kg / 7 lb 1 oz vs. 3.3 kg / 7 lb 4 oz) and more likely to be born small for their gestational age (11% vs. 6.6% of omnivore babies). By age two, vegans had caught up and differences in weight, length, and head circumference were clinically insignificant.

Reference

Avital K, Fliss-Isakov N, Shahar DR, Blaychfeld-Magnazi M, Ben-Avraham S, Tepper S, Hamiel U. Growth Trajectories in Infants From Families With Plant-Based or Omnivorous Dietary Patterns. JAMA Netw Open. 2026 Feb 2;9(2):e2557798.

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Two 2026 meta-analyses (released in one month of each other) reached different conclusions about vegans and colorectal cancer. Here are the differences.

Dunneram et al. conducted a pooled analysis using individual participant data from 9 cohorts comprising 1.8 million people and 220,387 incident cancers, with a median 16-year follow-up. Aune et al. conducted a more traditional aggregate meta-analysis, combining published summary estimates from 7 cohorts. Dunneram applied false discovery rate (FDR) correction across 16 associations; Aune did not apply multiplicity correction.

Despite the large number of cohorts, for vegans and colorectal cancer, there were much fewer cohorts to draw data from (as shown in the table below).

The two studies overlap considerably in their vegan data, both include AHS-2 and EPIC-Oxford/OVS, yet reach different conclusions. The key differences are that Dunneram et al. includes additional cohorts contributing vegan cases, uses individual participant data allowing more precise adjustment, applies FDR correction, and analyzes rectal cancer separately. Aune’s two contributing studies point in opposite directions (AHS-2: RR 0.88; EPIC-Oxford: RR 1.29), producing a null result.

The vegan colorectal cancer question remains unresolved. Case numbers are small across all studies; Dunneram’s finding rests on roughly 93 vegan cases.

Both papers acknowledge that diet adherence duration, calcium intake, and long-chain omega-3 intake may be important factors not fully captured by diet group classification alone.

I’m in the process of reviewing the literature on omega-3s and colorectal cancer. As for calcium, in her post about calcium and the colon, Ginny Messina makes an interesting point that it might be important to eat a significant amount of calcium that is not absorbed, so that it can bind to bile acids and fatty acids in the colon and prevent them from damaging the colon lining. She’s inspired me to make sure I don’t forget to include some calcium-fortified orange juice and/or soymilk each day.

I’ve updated Cancer and Vegan Diets with this new information.

References

Aune D, Schlesinger S, Sobiecki JG. Vegetarian and vegan diets and cancer incidence: a systematic review and meta-analysis of prospective studies. Eur J Epidemiol. 2026.

Dunneram Y, Lee JY, Watling CZ, Lawson I, Parsaeian M, Fraser GE, Butler FM, Prabhakaran D, Shridhar K, Kondal D, Mohan V, Ali MK, Narayan KMV, Tandon N, Tong TYN, Travis RC, Chiu THT, Lin MN, Lin CL, Yang HC, Liang YJ, Greenwood DC, Reeves GK, Papier K, Floud S, Sinha R, Liao LM, Loftfield E, Cade JE, Key TJ, Perez-Cornago A. Vegetarian diets and cancer risk: pooled analysis of 1.8 million women and men in nine prospective studies on three continents. Br J Cancer. 2026 Feb 27.

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There has been no prospective data on cognition in a cohort that includes a sizable number of vegans. Until now. Maybe.

The Chinese Longitudinal Healthy Longevity Survey (CLHLS) tests cognition every 2–3 years. They deliberately recruit very old adults. Field teams identify centenarians first, then enroll nearby 90–99 year-olds and 80–89 year-olds; they also include 65–79 year-olds (Zeng, 2017).

In January, researchers released a report analyzing prospective cognitive impairment across diet groups among people aged 65 and older, using data from 6 waves of the CLHLS cohort from 2002 to 2018 (Song, 2026).

They defined the diet groups as:

• vegan – abstaining from all animal products
• lacto-ovo vegetarian – consuming dairy and/or eggs but no meat or fish
• pescatarian – consuming fish but no meat
• omnivore – consuming meat at any frequency

Over the course of about 16 years, the vegan group had a trend toward higher rates of cognitive impairment than omnivores (as shown in Figure 3 of their paper). Unfortunately, they didn’t report exact numbers, follow-up duration, or number of measurements. Their Figure 3 indicates that the vegan group had a higher probability of cognitive impairment than omnivores by roughly 1–2% from about age 80 to 100; statistical significance wasn’t reported.

There’s a strong caveat to extrapolating this finding to vegans in general. It seems likely that most of these “vegans” weren’t necessarily choosing to be vegan. Although Song et al. defined vegan as “abstaining from animal products,” there’s nothing to suggest that the diet assessment tool did anything more than measure what people ate, as distinct from what foods they proactively abstain from or what they identify as. That 491 of the 3,554 “vegans” in the study were over 100 years old at baseline adds to my skepticism; it seems very unlikely that the researchers would have encountered so many vegan centenarians, or, if they did, that they wouldn’t have mentioned finding clusters of vegan centenarians. For cohorts that actively recruit large numbers of vegetarians and vegans, such as the Adventist Health Study-2 and EPIC-Oxford, it’s much safer to assume that participants are truly “abstaining” from animal products.

This study also included a cross-sectional arm using baseline characteristics. The vegan group had an odds ratio of being cognitively impaired of 1.32 (95% CI 1.22-1.45, p < 0.001). This was after adjusting for age, gender, social and lifestyle factors (including residence in a city, town, or rural area, and education level), and comorbidities. Adjusting for residence decreased the association for vegans, but didn’t ameliorate it.

Here’s the prevalence of cognitive impairment among diet groups in the CLHLS using cross-sectional data that isn’t age-adjusted:

• vegans: 37.9%
• lacto‐ovo-vegetarians: 42.4%
• pescatarians: 33.7%
• omnivores: 34.4%

While the differences in cognitive impairment between the vegan and omnivore groups was statistically significant, they weren’t massive.

Many in the vegan group were from rural areas (67%) and had little or no formal schooling (70%). I couldn’t find evidence of a nationwide program in China that screens rural older people for vitamin B12 deficiency or provides B12 supplements. If older people avoid or can’t access animal-source foods, and also lack B12-rich fortified foods or supplements, their cognition could likely worsen over time.

They also cross-sectionally analyzed two other cohorts: the Survey of Health, Ageing and Retirement in Europe (SHARE) and the United States National Health and Nutrition Examination Survey (NHANES). SHARE didn’t distinguish vegans from other vegetarians. NHANES had 32 vegans who, at baseline, had a non-statistically significant increased odds ratio of cognitive impairment in the fully adjusted model (OR 1.67, 95% CI: 0.55-5.10).

While this data is concerning, it’s also not surprising: when animal products are absent from the diet long term, and B12 isn’t obtained from fortified foods or supplements, B12 deficiency is highly likely and can impair cognition. To understand the impact of a vegan diet on cognition, people who identify as vegans should be purposefully recruited, their vitamin B12 and other nutrient intakes measured, and their cognition assessed over time.

References

Song Z, He Z, Wang X, Lei C, Ding M, Sun Z, Cao J, Ren G, Di Y. A gradient risk of cognitive impairment with vegetarian diets in older adults: highest for vegan and potential benefit for pescatarian. Food Res Int. 2026 Apr 1;229:118455.

Zeng Y, Feng Q, Gu D, Vaupel JW. Demographics, phenotypic health characteristics and genetic analysis of centenarians in China. Mech Ageing Dev. 2017 Jul;165(Pt B):86-97.

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Dunneram et al. (2026) conducted a meta-analysis of cancer incidence among nine cohorts that included a large number of vegetarians. It found a higher rate of colorectal cancer among vegans.

I’ve added details about the study to the section, Specific cancer incidence among vegans of Cancer and Vegan Diets. I’ve excerpted the Summary here:

A meta-analysis by Dunneram et al. (2026) found higher risks of colorectal cancer in vegans, driven in part by rectal cancer. After removing the first four years of follow-up, the colorectal finding attenuated and was no longer statistically significant, consistent with potential reverse causation or inclusion of early cases. However, a higher rate of rectal cancer for vegans remained statistically significant even after removing the first four years of follow-up and among never smokers.

The overall lower rates of cancer seen among vegans in the AHS-2 and British vegetarian cohorts, should still give vegans an overall benefit in terms of cancer. However, it’s worth monitoring these findings. Vegan case numbers were small (e.g., rectal n≈35 across cohorts), so estimates are imprecise.

In AHS-2 and the British vegetarian cohort, vegans had lower overall cancer incidence; these cohorts suggest vegans tend to have lower overall cancer risk, even though site-specific trends vary.

In the British cohort, colorectal cancer in vegans wasn’t significantly different from regular meat-eaters but trended higher (RR 1.31, 95% CI 0.82–2.11). In AHS‑2, vegans trended lower for colorectal (HR 0.88, 95% CI 0.64–1.22) and higher for rectal (HR 1.13, 95% CI 0.60–2.13), both nonsignificant.

In Dunneram et al.’s meta-analysis, lacto‑ovo‑vegetarians had similar colorectal cancer rates as regular meat‑eaters; pescatarians had lower colon cancer, including after excluding the first four years and among never-smokers. This pattern could reflect nutrient differences; Dunneram et al. noted that vegans had the lowest average calcium and lower long‑chain omega‑3 intakes across cohorts.

We don’t want to be alarmist—the statistics here aren’t strong, and observational data can’t prove causation. We already urge vegans to meet calcium needs with fortified foods (and supplements if needed). I’m more hesitant to recommend universal EPA/DHA supplementation, but the rectal-cancer signal has me re‑evaluating. I’ll be reviewing the EPA/DHA evidence in more depth.

Stay tuned!

Reference

Dunneram Y, Lee JY, Watling CZ, Lawson I, Parsaeian M, Fraser GE, Butler FM, Prabhakaran D, Shridhar K, Kondal D, Mohan V, Ali MK, Narayan KMV, Tandon N, Tong TYN, Travis RC, Chiu THT, Lin MN, Lin CL, Yang HC, Liang YJ, Greenwood DC, Reeves GK, Papier K, Floud S, Sinha R, Liao LM, Loftfield E, Cade JE, Key TJ, Perez-Cornago A. Vegetarian diets and cancer risk: pooled analysis of 1.8 million women and men in nine prospective studies on three continents. Br J Cancer. 2026 Feb 27.

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In June, the Adventist Health Study‑2 released 7.9‑year follow‑up results on cancer incidence by diet group. I revised the VeganHealth page on vegan diets and cancer with a stronger focus on vegans and added a section on whole‑food plant‑based diets to slow cancer progression.

Here’s a quick summary:

Vegans appear to have ~20% lower cancer incidence than regular meat-eaters (i.e., not including pescatarians and flexitarians). No sufficiently large or long studies have assessed cancer mortality among vegans. Lower average body mass index (BMI) explains part of the reduction; other dietary factors likely contribute. Whole‑food plant‑based diets show some promise for slowing progression, but evidence is limited; the plant‑based component may matter more than the whole‑food component.

Read the full article: Vegan Diets and Cancer.

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Until now, I’ve suggested that vegans supplement with zinc if they have signs of deficiency, especially frequent colds or cracks in the corners of the mouth. Recent research suggests that, in general, vegans might improve their health by supplementing with zinc.

A study by Vallboehmer et al. (Germany, 2025) found a high percentage of vegans to be zinc deficient, with evidence that it’s impacting their immune system. Klein et al. (Germany, 2023) also found that a high percentage of vegans are likely zinc-deficient.

For those who opt to supplement, I recommend about 50-100% of the RDA. For vegan adults, the recommended intake is approximately 5 to 10 mg per day. I supplement with 15 mg per day—5 mg in a multivitamin, and a 10 mg zinc-only supplement. I usually take them at different times, just in case it helps with absorption.

I’ve updated the section, Zinc Absorption and Status of Vegans, on VeganHealth.org with the details of this research.

Klein L, Dawczynski C, Schwarz M, Maares M, Kipp K, Haase H, Kipp AP. Selenium, Zinc, and Copper Status of Vegetarians and Vegans in Comparison to Omnivores in the Nutritional Evaluation (NuEva) Study. Nutrients. 2023 Aug 11;15(16):3538.

Vallboehmer F, Schoofs H, Rink L, Jakobs J. Zinc supplementation among zinc-deficient vegetarians and vegans restores antiviral interferon-α response by upregulating interferon regulatory factor 3. Clin Nutr. 2025 Jun 21;51:161-173.

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