Thiamine (vitamin B1),¹pantothenic acid (vitamin B5),² and other B vitamins³ have all been shown to play a role in wound healing in animal studies. For this reason, although human research is lacking, some alternative healthcare practitioners recommend a high-potency B vitamin supplement to promote wound healing.

Several preliminary studies,^{4, 5, 6, 7} though not all,⁸ have found a surprisingly high incidence of iron and B vitamin deficiency among people with recurrent canker sores. Treating these deficiencies has been reported in preliminary^{9, 10} and controlled¹¹ studies to reduce or eliminate recurrences in most cases. Supplementing daily with B vitamins 300 mg vitamin B1, 20 mg vitamin B2, and 150 mg vitamin B6 has been reported to provide some people with relief.¹² Thiamine (B1) deficiency specifically has been linked to an increased risk of canker sores.¹³ The right supplemental level of iron requires diagnosis of an iron deficiency by a healthcare professional using lab tests.

Preliminary reports in the 1940s claimed that rosacea improved with oral supplements or injections of B vitamins^{14, 15, 16} On the other hand, one report exists of rosacea-like symptoms in a patient taking 100 mg per day of vitamin B6 and 100 mcg per day of vitamin B12; these symptoms subsided when the supplements were discontinued.¹⁷ More research is needed to evaluate the potential benefits or hazards of B vitamins for rosacea.

Deficiencies of B-complex vitamins are common with chronic alcohol use.¹⁸ The situation is exacerbated by the fact that alcoholics have an increased need for B vitamins.¹⁹ It is possible that successful treatment of B-complex vitamin deficiencies may actually reduce alcohol cravings, because animals crave alcohol when fed a B-complex-deficient diet.²⁰ Many doctors recommend 100 mg of B-complex vitamins per day.

The B-complex vitamins are important for athletes, because they are needed to produce energy from carbohydrates. Exercisers may have slightly increased requirements for some of the B vitamins, including vitamin B2, vitamin B6, and vitamin B5 (pantothenic acid);²² athletic performance can suffer if these slightly increased needs are not met.²³ However, most athletes obtain enough B vitamins from their diet without supplementation,²⁴ and supplementation studies have found no positive effect on performance measures for vitamin B2,^{25, 26} vitamin B3 (niacin),²⁷ or vitamin B6.²⁸ On the contrary, large amounts of niacin have been shown to impair endurance performance.²⁹

B vitamins, particularly vitamin B6, have also been used for ADHD. Deficient levels of vitamin B6 have been detected in some ADHD patients.³⁰ In a study of six children with low blood levels of the neurotransmitter (chemical messenger) serotonin, vitamin B6 supplementation (15-30 mg per 2.2 pounds of body weight per day) was found to be more effective than methylphenidate (Ritalin). However, lower amounts of vitamin B6 were not beneficial.³¹ The effective amount of vitamin B6 in this study was extremely large and could potentially cause nerve damage, although none occurred in this study. A practitioner knowledgeable in nutrition must be consulted when using high amounts of vitamin B6. High amounts of other B vitamins have shown mixed results in relieving ADHD symptoms.^{32, 33}

According to preliminary studies from many years ago, lack of hydrochloric acid (HCl) secretion by the stomach was associated with chronic hives, presumably as a result of increasing the likelihood of developing food allergies. In one such study, 31% were diagnosed as having achlorhydria (no gastric acid output), and 53% were shown to be hypochlorhydric (having low gastric acid output).³⁴ In a related study, treatment with an HCl supplement and a vitamin B-complex supplement helped to treat people with hives.³⁵Betaine HCl is the most common hydrochloric acid-containing supplement; it comes in tablets or capsules measured in grains or milligrams. One or more tablets or capsules, each containing 5-10 grains (325-650 mg) are typically taken with a meal that contains protein. Diagnosis of a deficiency of HCl and supplementation with HCl should be supervised by a doctor.

One trial studying postmenopausal women combined hormone replacement therapy with magnesium (600 mg per day), calcium (500 mg per day), vitamin C, B vitamins, vitamin D, zinc, copper, manganese, boron, and other nutrients for an eight- to nine-month period.³⁷ In addition, participants were told to avoid processed foods, limit protein intake, emphasize vegetable over animal protein, and limit consumption of salt, sugar, alcohol, coffee, tea, chocolate, and tobacco. Bone density increased a remarkable 11%, compared to only 0.7% in women receiving hormone replacement alone.

Many years ago, research linked B vitamin deficiencies to PMS in preliminary research.^{38, 39} Based on that early work, some doctors recommend B-complex vitamins for women with PMS.⁴⁰

During a ten-year period, doctors at the North Nassau Mental Health Center in New York treated approximately 11,000 people with schizophrenia with a megavitamin regimen that included vitamin C (up to 4 grams per day), vitamin B3 either as niacin or niacinamide (up to 4 grams per day), vitamin B6 (up to 800 mg per day), and vitamin E (up to 1,200 IU per day). During that time, not a single new case of TD was seen, even though many of the people were taking neuroleptic drugs.⁴¹ Another psychiatrist who routinely used niacinamide, vitamin C, and vitamin B-complex over a 28-year period rarely saw TD develop in her patients.⁴² Further research is needed to determine which nutrients or combinations of nutrients were most important for preventing TD. The amounts of niacinamide and vitamin B6 used in this research may cause significant side effects and may require monitoring by a doctor.

An early report described the use of PABA (para-aminobenzoic acid) a compound commonly found in B-complex vitamins for vitiligo. Consistent use of 100 mg of PABA three or four times per day, along with an injectable form of PABA and a variety of hormones tailored to individual needs, resulted, in many cases, in repigmentation of areas affected by vitiligo.⁴³