Vitamin B Complex

What it is

The B vitamins are water-soluble. Most act as coenzymes, that is, as tools of enzymes: thiamine, riboflavin, niacin and pantothenic acid in the breakdown of carbohydrates and fats, B6 in protein metabolism, folate and B12 in cell division and blood formation.

Folate, B12 and B6 share a special task: they break down homocysteine, an intermediate product of protein metabolism. High homocysteine is considered a risk factor for cardiovascular disease and is associated with more dementia in observational studies. This gave rise to the hope that these diseases could be prevented with B vitamins. Exactly that was tested in large studies.

A B complex supplement usually contains all eight vitamins in one capsule. The amounts vary widely. An EFSA market analysis of 2,210 supplements containing vitamin B6 found a median of 1.4 mg per serving; half were between 1.01 and 2.0 mg, only 1.4 percent above 20 mg.

Who really benefits

For some groups, the question of benefit is easy to answer. Between 3 and 43 percent of older people have a B12 deficiency, particularly with chronic inflammation of the stomach lining, atrophic gastritis. Anyone on a vegan diet gets B12 practically only from supplements or fortified foods. The diabetes drug metformin and acid blockers reduce B12 absorption, as do gastrointestinal surgery, celiac disease and Crohn’s disease.

For everyone who could become pregnant, there is a recommendation of 400 µg of folic acid per day in addition to food, because it lowers the risk of neural tube defects in the child. According to the US health agency CDC, the gene variant MTHFR C677T does not change this: folic acid is recommended for carriers too. Some of them might additionally benefit from the active form 5-MTHF; there is no evidence of a general advantage of methylated forms.

What users are looking for

Most people reach for a B complex against tiredness, in stressful phases, after alcohol or as nerve protection. Many report feeling more alert and resilient, others notice no difference. That fits the study situation. Those who were poorly supplied beforehand are most likely to feel something; with a good starting point, little is to be expected. If you notice persistent tiredness, a blood test including B12 and folate is the more sensible first step than a supplement on suspicion.

What the studies show

Cochrane review on heart and stroke 2017

15 randomized trials with 71,422 participants, followed for 1 to 7.3 years, tested B6, B12 and folic acid against placebo. Heart attacks occurred in 7.1 versus 6.0 percent (relative risk 1.02), and 11.7 versus 12.3 percent died (1.01), both without a difference. Strokes were somewhat less frequent with the vitamins. The authors consider further trials on this question unlikely to be fruitful; the data are stable.

VITACOG: brain shrinkage in memory problems 2010

271 people over 70 with mild cognitive impairment took 0.8 mg of folic acid, 0.5 mg of B12 and 20 mg of B6 daily or placebo for 24 months. 168 completed both MRI measurements. Brain atrophy, the primary endpoint, was clearly slower with the vitamins, especially with high homocysteine. The B6 amount in this trial is above today’s EFSA upper limit of 12 mg.

Cognitive aging in 11 large trials 2014

An international analysis used the individual data of 22,000 participants from 11 trials. Although homocysteine fell by about a quarter, neither memory nor processing speed nor global cognitive performance changed. An effect of more than one month of brain aging gained per year of treatment could be ruled out.

B vitamins and mood 2019

The meta-analysis included 16 randomized trials with 2,015 participants that gave at least 3 B vitamins for at least 4 weeks. 11 of 18 papers reported a positive effect. Pooled, stress improved significantly, depressive symptoms narrowly missed significance (p = 0.07) and anxiety did not improve at all. People with poor supply or low mood benefited most.

Where the data stop

The big plan to prevent heart attacks and dementia with B vitamins has not worked out in well-supplied people. Homocysteine falls reliably, but heart attacks and mortality do not change. On cognitive aging, the largest analysis with 22,000 people found no effect. Another meta-analysis of 95 studies did see an advantage, but it amounted to only 0.14 points on the Mini-Mental test and appeared only with treatments lasting over 12 months. The often-cited link between folate and less dementia (hazard ratio 0.61) comes from observational studies on diet, not from trials with supplements.

For energy and nerves, the authorized health claims describe the function of a nutrient, not an additional benefit when supply is adequate. That stress or exercise substantially increases requirements could not be demonstrated with robust figures. For hair, skin and nails, the benefit of biotin without deficiency rests only on case reports and small studies.

Status, approval and legal

In Germany, B complex supplements are food supplements; B12 and folic acid are also available as medicines against deficiency states. Binding EU maximum levels for vitamins in food supplements do not yet exist. In 2024, the BfR proposed a maximum level for vitamin B6 of 0.9 mg per daily dose after EFSA had lowered the tolerable upper limit for adults from 25 to 12 mg in 2023. Both assessments continue to rely on a case-control study from 1987 in which about 100 mg a day were taken on average. Authorized claims include that riboflavin, niacin, pantothenic acid, B6, folate and B12 contribute to the reduction of tiredness and that biotin contributes to the maintenance of normal hair and skin. B vitamins are not relevant to doping.

Safety

The most important risk is vitamin B6. High long-term doses can damage nerves in the hands and feet, with tingling and numbness. EFSA sets the upper limit for adults at 12 mg per day, for children at 3.2 to 10.7 mg depending on age. Nobody reaches this through a normal diet; high-dose supplements or the combination of several products are what matter here. Folic acid should not exceed 1,000 µg per day, because it can mask the anemia of a B12 deficiency while nerve damage continues. Niacin as nicotinic acid often triggers a harmless but unpleasant flush from 30 to 50 mg; nicotinamide does not. Biotin distorts laboratory tests: as little as 10 mg interfered with thyroid values, and in 2019 the FDA warned of false heart attack tests. Let them know before blood draws. For B12 there is no upper limit because of its low toxicity.

Sources

• Martí-Carvajal et al., Cochrane Database Syst Rev 2017
• Clarke et al., Am J Clin Nutr 2014
• Smith et al., PLoS One 2010 (VITACOG)
• Wang et al., Nutr Rev 2022
• Young et al., Nutrients 2019
• EFSA NDA Panel, upper limit for vitamin B6, EFSA Journal 2023
• BfR, proposed maximum levels for vitamin B6, Opinion 008/2024
• NIH Office of Dietary Supplements, Vitamin B12
• NIH Office of Dietary Supplements, Folate
• NIH Office of Dietary Supplements, Biotin