A combination of vitamin B1, vitamin B6, and vitamin B12 has proved useful for preventing a relapse of a common type of back pain linked to vertebral syndromes,¹ as well as reducing the amount of anti-inflammatory medications needed to control back pain, according to double-blind trials.² Typical amounts used have been 50–100 mg each of vitamins B1 and B6, and 250–500 mcg of vitamin B12, all taken three times per day.^3,4 Such high amounts of vitamin B6 require supervision by a doctor.

Some studies have found low vitamin B1 (thiamine) levels and reduced activity of some thiamine-dependent enzymes among people with fibromyalgia.^5,6 The clinical significance of these findings remains unknown.

A combination of vitamin B1, vitamin B6, and vitamin B12 has proved useful for preventing a relapse of a common type of back pain linked to vertebral syndromes,⁷ as well as reducing the amount of anti-inflammatory medications needed to control back pain, according to double-blind trials.⁸ Typical amounts used have been 50–100 mg each of vitamins B1 and B6, and 250–500 mcg of vitamin B12, all taken three times per day.^9,10 Such high amounts of vitamin B6 require supervision by a doctor.

Vitamin B1 is involved in nerve transmission in parts of the brain (called cholinergic neurons) that deteriorate in Alzheimer’s disease.^11,12 The activity of vitamin B1-dependent enzymes has been found to be lower in the brains of people with Alzheimer’s disease.¹³ It has therefore been suggested that vitamin B1 supplementation could slow the progression of Alzheimer’s disease. Two double-blind trials have reported small but significant improvements of mental function in people with Alzheimer’s disease who took 3 grams a day of vitamin B1, compared to those who took placebo.^14,15 However, another double-blind trial using the same amount for a year found no effect on mental function.¹⁶

In a double-blind trial, adolescents living in India who were suffering from dysmenorrhea took 100 mg of vitamin B1 (thiamine) per day for three months. Eighty-seven percent of those treated experienced marked relief of dysmenorrhea symptoms.¹⁷ However, vitamin B1 deficiency is relatively common in India, whereas it is rare in the Western world, except among alcoholics. It is not known whether vitamin B1 supplementation would relieve dysmenorrhea in women who are not B1 deficient.

In a double-blind trial, adolescents living in India who were suffering from dysmenorrhea took 100 mg of vitamin B1 (thiamine) per day for three months. Eighty-seven percent of those treated experienced marked relief of dysmenorrhea symptoms.¹⁸ However, vitamin B1 deficiency is relatively common in India, whereas it is rare in the Western world, except among alcoholics. It is not known whether vitamin B1 supplementation would relieve dysmenorrhea in women who are not B1 deficient.

Vitamin B1, given as intramuscular injections of 120 mg daily for several days before surgery, resulted in less reduction of immune system activity after surgery in a preliminary trial.¹⁹ In a controlled trial, an oral B vitamin combination providing 100 mg of B1, 200 mg of vitamin B6, and 200 mcg of vitamin B12 daily given for five weeks before surgery and for two weeks following surgery also prevented post-surgical reductions in immune activity.²⁰ However, no research has explored any other benefits of B vitamin supplementation in surgery patients.

In HIV-positive people with B-vitamin deficiency, the use of B-complex vitamin supplements appears to delay progression to and death from AIDS.²¹ Thiamine (vitamin B1) deficiency has been identified in nearly one-quarter of people with AIDS.²² It has been suggested that a thiamine deficiency may contribute to some of the neurological abnormalities that are associated with AIDS. Vitamin B6 deficiency was found in more than one-third of HIV-positive men; vitamin B6 deficiency was associated with decreased immune function in this group.²³ In a population study of HIV-positive people, intake of vitamin B6 at more than twice the recommended dietary allowance (RDA is 2 mg per day for men and 1.6 mg per day for women) was associated with improved survival.²⁴ Low blood levels of folic acid and vitamin B12 are also common in HIV-positive people.²⁵

Blood levels of vitamin B1 (thiamine) have been found to be low in people with type 1 diabetes, and low levels are correlated with greater risk of diabetes-related anemia and other complications.^26,27,28 Supplementing with B1, along with vitamins B6 and B12, was found to reduce high levels of homocysteine in children type 1 diabetes in one placebo-controlled trial. High homocysteine levels are generally correlated with blood vessel dysfunction and reducing high levels may help prevent vascular complications of diabetes. In this trial, improvement in markers of kidney function were also seen.²⁹

Several controlled trials have evaluated the effect of benfotiamine, a fat-soluble form of vitamin B1, on diabetic neuropathy in participants with type 1 and type 2 diabetes. In one of these trials, 600 mg per day of benfotiamine was more effective than 300 mg per day or placebo for reducing neuropathic pain after six weeks; in a three-week trial, those receiving 400 mg per day of benfotiamine had greater pain reduction than those receiving placebo.^30,31 However, 300 mg of benfotiamine daily had no benefits on nerve function relative to placebo in people with type 1 diabetes after 24 months, suggesting this dose may be too low to be helpful.³²

A controlled trial in Africa found that supplementing with both vitamin B1 (25 mg per day) and vitamin B6 (50 mg per day) led to significant improvement of symptoms of diabetic neuropathy after four weeks.³⁵ However, since this was a trial conducted among people in a vitamin B1–deficient developing country, these improvements might not occur in other people with diabetes. Another trial found that combining vitamin B1 (in a special fat-soluble form) and vitamin B6 plus vitamin B12 in high but variable amounts led to improvement in some aspects of diabetic neuropathy in 12 weeks.³⁶ As a result, some doctors recommend that people with diabetic neuropathy supplement with vitamin B1, though the optimal level of intake remains unknown.

The small proportion of people with cardiomyopathy whose disease is due to severe vitamin B1 (thiamine) deficiency (known as wet beri beri) generally require intravenous vitamin B1, followed by oral supplementation. Vitamin B1 does not appear to be helpful for other types of cardiomyopathy. People requiring vitamin B1 for cardiomyopathy must first be diagnosed as having wet beri beri, and treatment must be supervised by a healthcare professional.