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Research · Supplements

B-complex vitamins

B vitamin combinations lowered homocysteine by about a quarter. In 15 trials, heart attacks and deaths did not change, and stroke fell 10%. In 11 trials, cognitive aging did not change. A pooled analysis found a small drop in stress. In diabetic kidney disease, B vitamins sped kidney decline and doubled vascular events.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement in the US.
Also called
B complex, B-50, B-100, vitamin B complex, B vitamins, Berocca, stress formula vitamins, folic acid with B6 and B12
Taken for
energy, stress, mood, fatigue, memory, brain health, heart health, homocysteine, hangovers, metabolism

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help2

Reported risks3

What people take it for, and what was found

Shown to help2

Moderate

Stress and mood

Shown to improve stress slightly in healthy and at-risk adults over 4 weeks or more, with no change in depression or anxiety. Bayer funded the review.

The numbers and sources
Effect
Across trials of 3 or more B vitamins for 4 weeks or longer, stress improved slightly (SMD 0.23, 95% CI 0.02 to 0.45). Depressive symptoms did not significantly change (SMD 0.15, 95% CI -0.01 to 0.32), nor did anxiety (SMD 0.03, 95% CI -0.13 to 0.20) [5].
Population
16 trials with 2,015 participants, healthy and at-risk, 12 pooled [5].
Sources
[5]
Caveats
Funded by Bayer HealthCare, which sells B-complex products [5].
Limited

Energy and fatigue in healthy people

Small trials found a B complex lengthened time to exhaustion in 32 young adults, and a B, C and mineral product raised self-rated stamina in working men.

The numbers and sources
Effect
In a double-blind crossover trial, 28 days of a B1, B2, B6 and B12 product (Ex PLUS) raised running time to exhaustion 1.26-fold over placebo (p < 0.05) and lowered blood lactate and ammonia during and after exercise [10]. In 198 employed men given a B complex with vitamin C and minerals or placebo for 28 days, the supplement group rated themselves higher for physical stamina across assessments, and for concentration, mental stamina and alertness after a working day at some time points [11].
Population
32 healthy adults aged 20 to 30, half women [10]. 198 men aged 30 to 55 in full-time work [11].
Sources
[10], [11]
Caveats
Two small trials of branded products. The second product also held vitamin C and minerals, so the B vitamins' share cannot be separated [11]. Ratings were self-reported, and effects in [11] appeared at some time points and not others.

Not shown to help2

Moderate

Heart attack, stroke and death

Not shown to change heart attack or death in 15 trials of B6, folic acid or B12. Stroke was about 10% lower.

The numbers and sources
Effect
Across 15 trials of vitamins B6, B9 or B12, heart attack (RR 1.02, 95% CI 0.95 to 1.10) and death from any cause (RR 1.01, 95% CI 0.96 to 1.06) did not change. Stroke was lower (RR 0.90, 95% CI 0.82 to 0.99) [1]. In HOPE-2, folic acid, B6 and B12 lowered homocysteine and did not change major cardiovascular events (RR 0.95, 95% CI 0.84 to 1.07) [2].
Population
71,422 participants in 15 trials [1]; 5,522 people aged 55 or older with vascular disease or diabetes, 5 years [2].
Sources
[1], [2]
Caveats
The Cochrane authors rated heart attack and mortality evidence high quality [1]. Trials tested folic acid, B6 and B12, not full B-complex products.
Moderate

Memory and cognitive aging

Not shown to change memory or thinking across 11 trials. One trial in older adults with mild cognitive impairment found slower brain shrinkage.

The numbers and sources
Effect
Across 11 trials, B vitamins lowered homocysteine by 26% to 28% and did not change memory, speed, executive function or global cognition (z score difference 0.00, 95% CI -0.05 to 0.06) [3]. In one trial in mild cognitive impairment, brain atrophy was 0.76% a year on B vitamins and 1.08% on placebo (P = 0.001) [4].
Population
22,000 participants in 11 trials, mean 2.3 to 5 years [3]; 168 people over 70 with mild cognitive impairment who completed MRI scans, 24 months [4].
Sources
[3], [4]
Caveats
The atrophy trial measured brain volume, not cognition. Its effect was concentrated in people with homocysteine above 13 µmol/L [4].

Doses studied

HOPE-2 used 2.5 mg folic acid, 50 mg B6 and 1 mg B12 a day [2]. The brain atrophy trial used 0.8 mg folic acid, 0.5 mg B12 and 20 mg B6 a day [4]. The diabetic kidney trial used 2.5 mg folic acid, 25 mg B6 and 1 mg B12 a day [6]. EFSA sets adult tolerable upper intake levels of 12 mg a day for vitamin B6, 1,000 µg for folic acid, 10 mg for nicotinic acid and 900 mg for nicotinamide. It found no adequate data to set one for thiamine, riboflavin, pantothenic acid or biotin, and no defined adverse effects for B12 [7]. For nerve damage from B6, see the vitamin B6 page.

Risks

Reported risks3

LimitedCommon

Cancer and death after folic acid with B12

Limited evidence: in two Norwegian trials, folic acid with B12 raised cancer from 8.4% to 10.0% and deaths from 13.8% to 16.1% in people with heart disease.

The numbers and sources
How common
Common: between 1 in 100 and 1 in 10 people.
Effect
Cancer was diagnosed in 10.0% given folic acid with B12 and 8.4% not given it (HR 1.21, 95% CI 1.03 to 1.41). Death from any cause was 16.1% against 13.8% (HR 1.18, 95% CI 1.04 to 1.33), driven mainly by lung cancer. B6 alone was not linked to any significant effect [8].
Population
6,837 people with ischemic heart disease in two Norwegian trials, median 39 months of treatment and 38 months of follow-up [8].
Sources
[8]
Caveats
Norway did not fortify food with folic acid. Across 15 trials, mortality did not change [1].
LimitedHow often is not known

Faster kidney decline and more vascular events in diabetic kidney disease

One trial found kidney filtration fell faster on B vitamins than placebo in 238 people with diabetic nephropathy, and vascular events or death were twice as common.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
At 36 months, kidney filtration fell 16.5 mL/min/1.73 m² on B vitamins and 10.7 on placebo (difference -5.8, 95% CI -10.6 to -1.1). Heart attack, stroke, revascularization or death was twice as common (HR 2.0, 95% CI 1.0 to 4.0) [6].
Population
238 people with type 1 or 2 diabetes and diabetic nephropathy at 5 Canadian centers [6].
Sources
[6]
Caveats
One trial. Dialysis need did not differ (HR 1.1) [6].
LimitedHow often is not known

More events after a heart attack on folic acid, B12 and B6

One trial found heart attack, stroke or sudden coronary death trended higher on folic acid, B12 and B6 than placebo after a heart attack, at the edge of significance.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In the group given all three vitamins, recurrent heart attack, stroke or sudden coronary death trended higher than placebo (RR 1.22, 95% CI 1.00 to 1.50, P = 0.05) [9].
Population
3,749 people within 7 days of a heart attack, median 40 months [9].
Sources
[9]
Caveats
One trial, with an interval touching 1.
Why limited
This rests on one trial, of 3,749 people. Strength counts independent studies that agree, so one trial is limited at any size.

Claims tested and not found

  1. That B vitamins prevent heart attacks by lowering homocysteine. Homocysteine fell and heart attacks did not change [1][2].
  2. That B vitamins slow cognitive aging. Across 11 trials and 22,000 people, cognition did not differ from placebo [3].
  3. That B vitamins protect the kidneys in diabetes. Kidney filtration fell faster on B vitamins than placebo [6].

Sources

  1. Martí-Carvajal AJ, Solà I, Lathyris D, et al. Homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database of Systematic Reviews. 2017. https://doi.org/10.1002/14651858.CD006612.pub5
  2. Lonn E, Yusuf S, Arnold MJ, et al. Homocysteine Lowering with Folic Acid and B Vitamins in Vascular Disease. New England Journal of Medicine. 2006. https://doi.org/10.1056/NEJMoa060900
  3. Clarke R, Bennett D, Parish S, et al. Effects of homocysteine lowering with B vitamins on cognitive aging: meta-analysis of 11 trials with cognitive data on 22,000 individuals. The American Journal of Clinical Nutrition. 2014. https://doi.org/10.3945/ajcn.113.076349
  4. Smith AD, Smith SM, de Jager CA, et al. Homocysteine-Lowering by B Vitamins Slows the Rate of Accelerated Brain Atrophy in Mild Cognitive Impairment: A Randomized Controlled Trial. PLoS ONE. 2010. https://doi.org/10.1371/journal.pone.0012244
  5. Young LM, Pipingas A, White DJ, et al. A Systematic Review and Meta-Analysis of B Vitamin Supplementation on Depressive Symptoms, Anxiety, and Stress: Effects on Healthy and 'At-Risk' Individuals. Nutrients. 2019. https://doi.org/10.3390/nu11092232
  6. House AA, Eliasziw M, Cattran DC, et al. Effect of B-Vitamin Therapy on Progression of Diabetic Nephropathy. JAMA. 2010. https://doi.org/10.1001/jama.2010.490
  7. European Food Safety Authority. Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Version 11. 2025. https://www.efsa.europa.eu/sites/default/files/assets/UL_Summary_tables.pdf
  8. Ebbing M, Bønaa KH, Nygård O, et al. Cancer Incidence and Mortality After Treatment With Folic Acid and Vitamin B12. JAMA. 2009. https://doi.org/10.1001/jama.2009.1622
  9. Bønaa KH, Njølstad I, Ueland PM, et al. Homocysteine Lowering and Cardiovascular Events after Acute Myocardial Infarction. New England Journal of Medicine. 2006. https://doi.org/10.1056/NEJMoa055227
  10. Lee MC, Hsu YJ, Shen SY, et al. A functional evaluation of anti-fatigue and exercise performance improvement following vitamin B complex supplementation in healthy humans, a randomized double-blind trial. International Journal of Medical Sciences. 2023. https://doi.org/10.7150/ijms.86738
  11. Kennedy DO, Veasey RC, Watson AW, et al. Vitamins and psychological functioning: a mobile phone assessment of the effects of a B vitamin complex, vitamin C and minerals on cognitive performance and subjective mood and energy. Human Psychopharmacology. 2011. https://doi.org/10.1002/hup.1216

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