B vitamins are a group of eight water-soluble nutrients that your body uses for energy production, nerve function, and dozens of metabolic processes. Unlike fat-soluble vitamins, your body cannot store them for long, which means you need a regular supply from food or supplements.

The eight B vitamins are: B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate/folic acid), and B12 (cobalamin).

Modern food processing strips away many B vitamins, which is why fortification programmes exist and why supplements have become popular. But do B complex supplements actually deliver measurable health benefits? I have gone through the clinical research on 17 commonly claimed benefits to see what holds up.

What the research says about B vitamin benefits

1. Diabetic peripheral neuropathy

Diabetic neuropathy affects the longest nerve fibres first, causing numbness, pain, and weakness in the feet and legs. Over 80% of non-traumatic amputations in diabetic patients begin with foot ulcers caused by this nerve damage.

A 2022 systematic review of 14 randomised controlled trials with 997 patients found that B vitamin supplementation improved both symptoms and clinical signs of diabetic peripheral neuropathy [1]. The combination typically included B1, B6, and B12.

My take: the evidence here is reasonably solid. B vitamins have established roles in nerve function, so this makes biological sense.

2. Mouth ulcers

Recurrent mouth ulcers (aphthous stomatitis) affect roughly 20% of the population. The causes range from stress and minor injuries to immune dysfunction.

A 2021 meta-analysis of 16 randomised controlled trials with 1,534 patients found that B vitamin treatment led to higher healing rates and lower recurrence compared with controls [2]. Ulcers also healed faster in the treatment groups.

Worth noting: the analysis excluded patients whose ulcers were caused by other medical conditions or treatments, so these findings apply specifically to common recurrent mouth ulcers.

3. Stroke prevention

About 85-90% of strokes are ischaemic, caused by blocked blood supply to the brain. High homocysteine levels are associated with increased stroke risk, and B vitamins (particularly folate, B6, and B12) help metabolise homocysteine.

A meta-analysis of 17 randomised controlled trials with 86,393 participants found that B vitamin supplementation reduced stroke risk [3]. The most effective combination was folic acid plus B6, followed by folic acid alone.

Interestingly, adding B12 to the mix seemed to reduce effectiveness slightly. Nobody is entirely certain why.

4. Cancer prevention

Here’s where expectations meet reality. A meta-analysis of 18 randomised controlled trials with 74,498 participants found that B vitamin supplementation had no effect on overall cancer incidence, cancer mortality, or all-cause mortality [4].

The one exception: supplementation did reduce the risk of skin melanoma specifically. But if you are taking B vitamins hoping to prevent cancer generally, the evidence does not support that.

5. Stress relief

Work-related stress costs billions annually in lost productivity and healthcare expenses. The theory behind B vitamins for stress is that they support neurotransmitter production and energy metabolism.

A 2019 systematic review and meta-analysis of 12 randomised, double-blind, placebo-controlled trials found that B vitamin supplementation did help relieve perceived stress [5]. However, it showed no significant benefit for depression or anxiety symptoms.

The effect was most pronounced in people with poor baseline nutrition or emotional status. If your diet is already adequate in B vitamins, extra supplementation may not make much difference.

6. Osteoporosis and fracture prevention

This one is disappointing. A meta-analysis of 8 randomised controlled trials with 26,707 participants examined whether daily B vitamin supplementation (folic acid, B6, and B12 alone or combined) could reduce osteoporotic fractures [6].

The result: no reduction in fracture risk, and no positive effect on bone turnover markers. The study participants had cardiovascular disease and relatively normal homocysteine levels, so results might differ in populations with elevated homocysteine, but the current evidence does not support B vitamins for bone health.

7. Acute lower back pain

Around 80-90% of lower back pain cases are “non-specific,” meaning no clear structural cause can be identified. Most resolve within weeks with conservative treatment.

A 2019 meta-analysis of 5 randomised controlled trials with 1,207 patients compared diclofenac (a common anti-inflammatory) alone versus diclofenac combined with B vitamins (B1, B6, B12) [7].

The combination therapy reduced treatment time by approximately 50%. This is one of the more practical findings, B vitamins seem to enhance the effectiveness of standard pain treatment for acute back pain.

8. Cognitive function in older adults

The relationship between homocysteine and dementia is well established: elevated homocysteine is associated with increased risk of cognitive impairment. Since B vitamins lower homocysteine, supplementation should help cognition. Right?

Not quite. A 2019 systematic review of 31 randomised placebo-controlled trials involving 17,029 older adults found that while B vitamins successfully lowered homocysteine, this did not translate into clear cognitive benefits [8].

The authors noted significant differences in supplement types, populations, study quality, and treatment duration across trials. More precisely designed studies might find effects in specific subgroups, but broad supplementation for cognitive protection is not supported.

9. Cardiovascular disease

Similar story here. A meta-analysis of 19 randomised controlled trials with 47,921 participants found that B vitamin supplementation lowered blood homocysteine and reduced stroke risk, but had no significant benefit for cardiovascular disease overall, myocardial infarction, coronary heart disease, cardiovascular death, or all-cause mortality [9].

B vitamins seem specifically protective against stroke, but not heart disease more broadly. The mechanism is unclear.

10. Glaucoma

Primary open-angle glaucoma involves progressive optic nerve damage. Elevated homocysteine has been proposed as a risk factor.

A meta-analysis of 37 studies found that primary open-angle glaucoma was indeed associated with elevated homocysteine levels [10]. However, there was no significant association with folate, B12, or B6 levels themselves.

This suggests the relationship might be more complex than simple B vitamin deficiency. Whether supplementation would help prevent or treat glaucoma remains unclear.

11. Psoriasis

Psoriasis is a chronic inflammatory skin condition affecting about 2% of the population, with higher rates in Caucasian and Scandinavian populations.

A meta-analysis found that psoriasis patients had significantly higher serum homocysteine and significantly lower serum folate compared with controls [11]. B12 levels showed no significant difference.

This suggests folate status might be relevant to psoriasis, but whether supplementation improves outcomes has not been adequately tested.

12. Air pollution damage (PM2.5)

This is an unusual application. PM2.5 exposure causes approximately 3.2 million deaths annually, primarily through cardiovascular effects.

A small crossover trial in 10 healthy adults found that PM2.5 exposure increased resting heart rate, altered heart rate variability, and affected immune cell counts [12]. B vitamin supplementation counteracted these effects.

Interesting finding, but 10 participants is far too few to draw firm conclusions. The results need replication in larger studies.

13. Depression

High homocysteine levels are associated with increased depression risk. Early studies suggested folic acid might enhance antidepressant effectiveness.

A clinical study found that adding folic acid (in the 5-MTHF form) to antidepressant treatment increased improvement rates from 16% to 40% and reduced time to response from 150 days to 85 days [13]. The dropout rate due to adverse effects was also halved in the combination group.

This is promising, but the study was relatively small and more large trials are needed before this becomes standard practice.

14. Obesity and body composition

A nutritional survey of 1,131 children aged 8-15 found that higher blood levels of B12 and folate were associated with lower body mass index and total body fat [14].

When looking at dietary intake, higher consumption of B1, B2, and folate was also associated with lower BMI.

The proposed mechanism involves B vitamins’ roles in carbohydrate and fat metabolism. However, this is observational data, showing correlation rather than causation. Whether B vitamin supplements can help with weight management has not been proven.

15. Schizophrenia

Schizophrenia is a chronic mental illness causing delusions, hallucinations, and cognitive impairment.

A meta-analysis of 18 randomised controlled studies with 832 participants found that adding B vitamins (B6, B12, and inositol) to standard medication reduced symptoms compared with medication alone [15]. The effect was stronger when supplementation began early in the disease course.

The authors noted that benefits were most apparent in people with genetic variants affecting B vitamin metabolism or with nutritional deficiencies.

16. Parkinson’s disease

Parkinson’s disease results from insufficient dopamine production due to brain cell degeneration.

A meta-analysis found that higher dietary intake of B6 was associated with 35% lower risk of Parkinson’s disease [16]. However, B12 and folate showed no association.

The proposed mechanism involves B6’s antioxidant properties and role in reducing oxidative stress. Importantly, this applies to B6 from food, not necessarily supplements.

17. DDT pesticide exposure and fertility

DDT was banned decades ago in most countries, but it persists in the environment and enters the food chain. High DDT blood levels can lower oestrogen and progesterone, affecting fertility.

A prospective cohort study found that adequate intake of B12 and folate before pregnancy could reduce adverse events from DDT exposure (including early pregnancy loss) and increase clinical pregnancy rates [17].

This is a fairly specific situation, but relevant for populations in regions where DDT exposure remains a concern.

Side effects of B vitamins

B vitamins are water-soluble, meaning excess amounts are generally excreted in urine rather than building up in the body. At normal doses, serious side effects are rare.

High doses or prolonged excessive intake may cause:

Dizziness
Frequent urination (due to water-soluble nature)
Dark urine
Digestive upset (constipation, diarrhoea, abdominal pain, nausea)
Skin flushing (particularly with niacin)
Nerve damage (paradoxically, from very high B6 doses)
Light sensitivity
Liver issues (with extremely high niacin doses)

Severe allergic reactions are rare but possible, presenting as itching, rash, swelling, or difficulty breathing. Stop use and seek medical attention if this occurs.

Safety precautions

1. Stay within recommended doses. A 36-month study of 238 patients with diabetic kidney disease found that high-dose B vitamins (folic acid 2,500 mcg, B6 25 mg, B12 1 mg) was associated with reduced kidney function and possibly increased cardiovascular events [18]. More is not better.

2. Yellow urine is normal. Riboflavin (B2) has a fluorescent yellow colour that will change your urine colour. This is harmless and just indicates excretion of excess.

3. Check with your doctor if you have liver or kidney problems. Impaired organ function affects how your body processes supplements.

4. Watch for drug interactions. B vitamins can interact with various medications, including some antibiotics, anti-seizure drugs, and chemotherapy agents. Discuss with your pharmacist or doctor.

5. Check for aspartame. Some B vitamin formulations contain artificial sweeteners. People with phenylketonuria need to avoid aspartame.

When to take B vitamins

B vitamins support energy production, so taking them in the morning makes sense. Evening doses may interfere with sleep for some people.

As water-soluble vitamins, they are best absorbed on an empty stomach, ideally 30 minutes before a meal or 2 hours after eating. However, if they cause stomach upset, taking them with food is fine.

References

Jiang DQ, et al. Efficacy of B vitamins in the treatment of diabetic peripheral neuropathy: A systematic review and meta-analysis. Diabetes Obes Metab. 2022;24(2):196-205. PMID: 34990506
Liu Y, et al. Efficacy of vitamin B in the treatment of oral ulcers: A systematic review and meta-analysis. Medicine (Baltimore). 2021;100(24):e26394. PMID: 34154361
Wang X, et al. Efficacy of folic acid supplementation in stroke prevention: a meta-analysis. Lancet. 2007;369(9576):1876-82. PMC4565665
Zhang SM, et al. Effect of combined folic acid, vitamin B6, and vitamin B12 on cancer risk in women: a randomized trial. JAMA. 2008;300(17):2012-21. PMID: 27495015
Young LM, et al. A Systematic Review and Meta-Analysis of B Vitamin Supplementation on Depressive Symptoms, Anxiety, and Stress. Nutrients. 2019;11(9):2232. PMID: 31527485
Yang J, et al. The effect of folic acid supplementation on fracture risk. Osteoporos Int. 2015;26(5):1515-24. PMC4384513
Machado GC, et al. B vitamins added to non-steroidal anti-inflammatory drugs for acute low back pain: a systematic review and meta-analysis. Curr Med Res Opin. 2019;35(11):1939-47. PMID: 31529101
Ford AH, et al. Effect of homocysteine lowering treatment on cognitive function: a systematic review and meta-analysis of randomized controlled trials. J Alzheimers Dis. 2019;67(1):169-80. PMID: 30949983
Clarke R, et al. Effects of lowering homocysteine levels with B vitamins on cardiovascular disease, cancer, and cause-specific mortality. Arch Intern Med. 2010;170(18):1622-31. PMID: 22652362
Roedl JB, et al. Homocysteine levels in patients with glaucoma: a systematic review and meta-analysis. Curr Eye Res. 2012;37(10):889-96. PMID: 22902176
Tsai TY, et al. Serum homocysteine, folate and vitamin B12 levels in patients with psoriasis: a systematic review and meta-analysis. Br J Dermatol. 2019;180(2):382-9. PMID: 30074615
Zhong J, et al. B vitamins attenuate the epigenetic effects of ambient fine particles in a pilot human intervention trial. Proc Natl Acad Sci USA. 2017;114(13):3503-8. PMC5377246
Papakostas GI, et al. L-methylfolate as adjunctive therapy for SSRI-resistant major depression: results of two randomized, double-blind, parallel-sequential trials. Am J Psychiatry. 2012;169(12):1267-74. PMID: 21311704
Gunanti IR, et al. Low serum vitamin B-12 and folate concentrations and low thiamin and riboflavin intakes are inversely associated with greater adiposity in Mexican American children. J Nutr. 2014;144(12):2027-33. PMID: 25411037
Firth J, et al. The effects of vitamin and mineral supplementation on symptoms of schizophrenia: a systematic review and meta-analysis. Psychol Med. 2017;47(9):1515-27. PMID: 28202095
Shen L. Associations between B Vitamins and Parkinson’s Disease. Nutrients. 2015;7(9):7197-208. PMID: 26343714
Bloom MS, et al. Associations between blood metals and fecundity among women residing in New York State. Reprod Toxicol. 2014;50:80-8. PMID: 25411282
House AA, et al. Effect of B-vitamin therapy on progression of diabetic nephropathy: a randomized controlled trial. JAMA. 2010;303(16):1603-9. PMID: 20424250