B complex

What is B complex, and which vitamins does it contain?

B vitamins are water-soluble vitamins that work as helper factors for many enzymes in the body. Eight are known: thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine and other B6 forms (B6), biotin (B7), folate (B9) and cobalamin (B12). The NIH reports that biotin is found only in supplements containing biotin, in B complex mixtures and in some multivitamin-mineral products; a “B complex” product is not required to contain all eight vitamins, and amounts vary by product. ^[9]

The table below shows the main function of each vitamin, the adult reference intake relayed by the NIH and the upper limit. The values were set in the US by the Food and Nutrition Board (FNB); “RDA” is for vitamins with sufficient evidence, and “AI” (adequate intake) is the value set when evidence is not sufficient. EFSA’s values may differ; for B6, the upper limits of the two organizations are given side by side below. The upper limit (UL) is “the highest daily intake at which harm is not expected”; that it has not been set does not mean unlimited safety and may also reflect that there are not enough data to set one.

According to the NIH’s pages, the FNB has not set a UL for B1, B2, B5, B7 and B12; it has set one for B3, B6 and folic acid. Details are given in the relevant sections. ^{[6] [1]}

Does B complex give energy?

Because B vitamins take part in energy metabolism, they are often presented as an “energy” product. Being a helper factor is not being a stimulant or a source of calories: vitamins contain no energy, they help the enzymes that obtain energy from food to work. The study’s authors also state in their own paper that B vitamins “do not directly provide energy.” ^[10]

For B12, the NIH says this: B12 is often presented as an energy booster and performance supporter because of its role in energy metabolism; however, no beneficial effect of B12 supplementation on performance has been seen when there is no nutritional deficiency. The B12 page covers this topic separately. ^[1]

Against this, there is a randomized double-blind crossover study examining 28 days of use of a B complex product containing B1, B2, B6 and B12. 32 healthy young people aged 20–30 (16 men, 16 women) received placebo and the product in sequence, 14 days apart; with the product, running time to exhaustion increased 1.26-fold, and blood lactate and ammonia levels during exercise were found lower than with placebo. One tablet of the product also contained vitamin E, inositol, calcium and taurine in addition to B vitamins; the B6 amount was 50 mg, that is, more than four times EFSA’s 12 mg/day upper limit. The study is small, examines a single product, and its findings are running time and blood metabolites; it was supported by the pharmaceutical company providing the product and by Taiwan’s Ministry of Science and Technology as an academia-industry project. It does not show a general B complex effect. ^[10]

In conclusion: in a person with a deficiency, fatigue may be a symptom of the deficiency and correction would be beneficial; when there is no deficiency, B complex is not considered to have been shown to give energy, and the evidence is insufficient.

Who may have low levels of certain B vitamins?

The NIH’s pages report that deficiency of certain vitamins is more likely in some groups. In these groups the problem is mostly with a single vitamin; a targeted evaluation (blood test, dietary history) rather than a mixture is needed.

• Vegans and vegetarians: B12. The NIH reports that B12 is naturally found only in animal foods, and that vegetarians and infants of vegan mothers are at risk. ^[1]
• Older adults: B12. According to the NIH, 3 to 43% of community-dwelling older adults, depending on the definition used, have deficiency by serum B12; especially those with atrophic gastritis. For thiamin as well, laboratory indicators suggesting some degree of deficiency are reported in up to 20–30% of older adults. ^{[1] [6]}
• People using metformin and acid-suppressing drugs: B12. The NIH reports that metformin can reduce B12 absorption and significantly lower serum B12; and that proton pump inhibitors and H2 receptor blockers can impair B12 absorption and lead to deficiency. ^[1]
• Pregnancy and those planning pregnancy: folate. The FNB has raised the folate RDA in pregnancy from 400 to 600 µg DFE. The NIH reports that all women and adolescents of childbearing age should get adequate folate to reduce the risk of neural tube defects and other birth defects. Details are in the folic acid guide. ^[2]
• Chronic alcohol users: thiamin. Wernicke-Korsakoff syndrome is seen about 8–10 times more often in people with chronic alcoholism than in the general population; it can also develop in severe gastrointestinal diseases. ^[6]
• Long-term antiepileptic users. The NIH reports that some antiepileptics increase the breakdown of B6 and may lower folate levels, and that biotin levels are also found low. The same source states that folate and B6 supplements can affect the blood levels of these drugs; the decision on a supplement is therefore made with the physician who prescribes the drug. ^{[3] [2] [9]}

In all of these groups, symptoms of deficiency may be confused with other diseases; complaints such as fatigue, numbness or pallor cannot be attributed to a B vitamin by looking at the symptom alone.

Does B complex prevent cardiovascular disease?

According to a hypothesis, folic acid, B12 and B6 could reduce cardiovascular risk by lowering homocysteine. According to the NIH’s B6 page, in the HOPE 2 study, in more than 5,500 adults with known cardiovascular disease, 5 years of B6 (50 mg/day), B12 (1 mg/day) and folic acid (2.5 mg/day) lowered homocysteine and reduced stroke risk by about 25%; however, the study had no separate B6 group. The NIH reports that most other large studies failed to show a reduction in cardiovascular events despite lowering homocysteine: the combination of B6 (50 mg/day) with folic acid and B12 was ineffective in 5,442 women; in the pooled analysis of two Norwegian studies containing B6 alone (40 mg/day) (6,837 patients with ischemic heart disease), no benefit was seen in major cardiovascular events. The NIH concludes that there is little evidence that B6 alone or with folic acid and B12 reduces the risk of cardiovascular disease and stroke. ^[3]

The Cochrane 2017 review pooling these studies (15 randomized studies followed for at least one year, 71,422 participants; end-stage kidney patients excluded) compared giving B6, B9 or B12 singly or together with placebo: there was no difference in heart attack (RR 1.02; 0.95–1.10) or all-cause death (RR 1.01; 0.96–1.06); a small reduction in stroke was reported (RR 0.90; 0.82–0.99). This does not show the separate effect of each vitamin. The same results are also given in the B6, B12 and folic acid guides. ^[11]

Can high-dose B complex products cause harm?

There are upper limits for some components of B complex products, and these limits may be exceeded in some high-dose products. Comparing the amount on the label in mg or µg with the upper limit is necessary for each vitamin individually in mixture products.

B6: nerve damage and two different upper limits

According to the NIH, taking 1–6 g of pyridoxine per day for 12–40 months can lead to severe and progressive sensory neuropathy with ataxia; symptoms generally resolve when the vitamin is stopped. Its other effects include painful skin lesions, photosensitivity, nausea and heartburn. The FNB assessed that neuropathy has been reported at doses below 500 mg/day, but that this effect was not seen in people treated with an average of 200 mg/day of B6 for up to 5 years, and, because of limited data, halved this dose and set the adult UL at 100 mg/day. ^[3]

EFSA’s 2023 opinion, on the other hand, accepts peripheral neuropathy as the critical effect and sets the UL at 12 mg/day for adults (including pregnant and breastfeeding women); this value is much lower than the NIH’s 100 mg. EFSA states that it is unlikely for the population in the EU to exceed this limit, the exception being people who regularly use food supplements containing high-dose B6. The two organizations’ values were derived with different data and uncertainty factors; they cannot be used interchangeably. ^[4]

Niacin: flushing and liver

According to the NIH, doses of 30–50 mg and above of the nicotinic acid form generally cause flushing: redness, burning, tingling and itching of the face, arms and chest. These symptoms are temporary and are considered by the NIH an uncomfortable, not toxic, side effect; however, headache, rash, dizziness and low blood pressure may accompany it. The nicotinamide form does not cause flushing. At pharmacological doses of 1,000–3,000 mg/day, more serious effects occur (hypotension that increases fall risk, impaired glucose tolerance, stomach complaints, vision problems); high doses over months to years can lead to liver toxicity, and this risk is higher with extended-release forms. The FNB’s niacin UL (adult 35 mg/day) applies only to supplemental niacin and was set on the basis of flushing; it does not cover doses used under medical supervision. The NIH also reports that in people using diabetes drugs, high-dose nicotinic acid can raise blood sugar. ^[5]

Folic acid and B12 relationship

The NIH reports that a high amount of folate corrects the megaloblastic anemia of B12 deficiency but does not correct neurological damage, so there is a concern that B12 deficiency may be masked; in recent years the concern has shifted to high folate possibly triggering or worsening the anemia and cognitive symptoms associated with B12 deficiency. The FNB’s folic acid UL is 1,000 µg/day and was set for synthetic forms (supplements, fortified foods); there is no UL for natural food folate. ^[2]

Vitamins without an upper limit

The FNB has not set an upper limit for B1, B2, B5, B7 and B12. The NIH relays, for B2, that no adverse effects were reported in people taking 400 mg per day for at least 3 months, but that the FNB nevertheless recommends caution regarding high amounts; for B5, that mild diarrhea and digestive discomfort were reported at very large doses such as 10 g per day; for B12, that no UL was set because of low toxicity. For biotin there is no UL, but high doses can distort tests (in the section on drug and test interactions). ^{[7] [8] [1]}

Why does B complex turn urine yellow?

Riboflavin (B2) is naturally yellow and fluoresces under ultraviolet light. According to the NIH, the body absorbs little riboflavin beyond 27 mg in a single dose and stores only small amounts; the excess is either not absorbed or the small amount absorbed is excreted in urine. The NIH says no adverse effects were reported in people taking 400 mg of riboflavin per day for at least 3 months. ^[7]

That orally taken riboflavin dyes urine yellow has also been seen in a controlled study: in 66 women given 400 mg of riboflavin or placebo the night before gynecologic surgery, urine seen during surgery in the riboflavin group was markedly more yellow than with placebo; surgeons used this effect to see the patency of the urinary tract. This study was conducted with a single dose and a high amount; it does not measure how much the color changes with the lower amounts in B complex products. A color change alone is not a sign of harm. ^[12]

With which drugs and tests does B complex interact?

• Biotin and blood tests. High-dose biotin can make tests such as thyroid hormones and troponin that use biotin-streptavidin technology read falsely high or falsely low; the FDA has issued a warning on this. Biotin may be present in B complex mixtures. ^[9]
• Metformin and stomach acid drugs affect B12, and antiepileptics affect B6, folate and biotin (above).
• Methotrexate. The NIH reports that people using methotrexate for cancer should consult their oncologist before folate supplementation; the supplement may interfere with the anti-cancer effect of methotrexate. ^[2]
• Sulfasalazine blocks folate absorption and can lead to folate deficiency; furosemide can increase thiamin loss. ^{[2] [6]}
• Antituberculosis drugs: cycloserine affects B6 loss, isoniazid affects niacin production. ^{[3] [5]}

This list is not comprehensive; a person using regular medication informs the physician and pharmacist which B vitamin is being taken.

Common misunderstandings about B complex

• “B vitamins give energy.” They help enzymes; no energy increase has been shown when there is no deficiency. ^[1]
• “Because it is a water-soluble vitamin, excess is harmless.” There are upper limits for B6, niacin and folic acid; B6 neuropathy and niacin liver toxicity have been reported. ^{[3] [5]}
• “Bright yellow urine shows B complex is causing harm.” Riboflavin is yellow and the absorbed excess is excreted in urine; the NIH states that no adverse effects were reported in people taking 400 mg of riboflavin per day for at least 3 months. ^{[7] [12]}
• “B complex contains every B vitamin equally.” The NIH reports that B complex products are mixtures containing several B vitamins; content varies by product. ^[9]

Evidence table: claim, population and limits

This guide does not recommend a personal dose; in product selection, pregnancy, chronic disease or medication use, the decision is made with a physician.