The niacin form of vitamin B3 is used by doctors to lower cholesterol levels, but niacin also lowers TG levels.¹ The amount of niacin needed to achieve worthwhile reductions in cholesterol and TG levels is several grams per day. Such quantities can cause side effects, including potential damage to the liver, and should not be taken without the supervision of a doctor. Some doctors recommend inositol hexaniacinate (a special form of vitamin B3) as an alternative to niacin. A typical amount recommended is 500 mg three times per day.^2,3 This form of vitamin B3 does not typically cause a skin flush and is said to be safer for the liver than niacin. However, the alleged safety advantage of inositol hexaniacinate needs to be confirmed by additional clinical trials. Moreover, it is not clear whether inositol hexaniacinate is as effective as niacin at lowering cholesterol and TG levels.

One controlled study compared a type of niacin (vitamin B3) known as inositol hexaniacinate to the drug pyridinolcarbamate for the treatment of skin ulcers caused by PVD.⁵ A placebo was not included in this trial, and both 1.2 grams daily of inositol hexaniacinate and 1.5 grams daily of the drug produced beneficial results in about half of the patients.

In the 1940s and 1950s, one doctor reported that supplemental niacinamide (a form of vitamin B3) increased joint mobility, improved muscle strength, and decreased fatigue in people with osteoarthritis.^14,15,16 In the 1990s, a double-blind trial confirmed a reduction in symptoms from niacinamide within 12 weeks of beginning supplementation.¹⁷ Although amounts used have varied from trial to trial, many doctors recommend 250 to 500 mg of niacinamide four or more times per day (with the higher amounts reserved for people with more advanced arthritis). The mechanism by which niacinamide reduces symptoms is not known.

The niacin form of vitamin B3 has been reported to be effective in relieving menstrual cramps in 87% of a group of women taking 200 mg of niacin per day throughout the menstrual cycle. They then took 100 mg every two or three hours while experiencing menstrual cramps.¹⁸ In a follow-up study, this protocol was combined with 300 mg of vitamin C and 60 mg of the flavonoid rutin per day, which resulted in a 90% effectiveness for relieving menstrual cramps.¹⁹ Since these two preliminary studies were published many years ago, no further research has explored the relationship between niacin and dysmenorrhea. Niacin may not be effective unless taken for seven to ten days before the onset of menstrual flow.

The niacin form of vitamin B3 has been reported to be effective in relieving menstrual cramps in 87% of a group of women taking 200 mg of niacin per day throughout the menstrual cycle. They then took 100 mg every two or three hours while experiencing menstrual cramps.²² In a follow-up study, this protocol was combined with 300 mg of vitamin C and 60 mg of the flavonoid rutin per day, which resulted in a 90% effectiveness for relieving menstrual cramps.²³ Since these two preliminary studies were published many years ago, no further research has explored the relationship between niacin and dysmenorrhea. Niacin may not be effective unless taken for seven to ten days before the onset of menstrual flow.

High doses of niacin (a form of vitamin B3), such as 2 to 3 grams per day, are sometimes recommended to lower high triglyceride and cholesterol levels in people with type 1 diabetes. However, niacin’s ability to reduce cardiovascular risk in the context of type 1 diabetes has not been established. It is important to note that niacin doses this high, particularly in extended release formulations, may cause flushing, stomach upset, and liver toxicity, and should be used by people with diabetes only with medical supervision.^26,27

Animal research suggests that niacinamide, a form of vitamin B3 with fewer side effects, may prevent toxic damage to the pancreatic cells that make insulin.²⁸ Although one intriguing study found niacinamide supplementation was associated with a lower incidence of type 1 diabetes in children at high risk, more recent studies have not confirmed a protective effect.^29,30

A controlled clinical trial in subjects with recently diagnosed type 1 diabetes found the addition of niacinamide (25 mg per day per kg of body weight; approximately 2–3 grams per day) to intensive insulin treatment led to greater improvement in HgA1c over two years, but other clinical trials have found no benefit on glucose metabolism in similar subjects.^31,32,33

Research has shown that supplementing with chromium (200 mcg per day)³⁷ or magnesium (340 mg per day)³⁸ can prevent blood sugar levels from falling excessively in people with hypoglycemia. Niacinamide (vitamin B3) has also been found to be helpful for hypoglycemic people.³⁹ Other nutrients, including vitamin C, vitamin E, zinc, copper, manganese, and vitamin B6, may help control blood sugar levels in diabetics.⁴⁰ Since there are similarities in the way the body regulates high and low blood sugar levels, these nutrients might be helpful for hypoglycemia as well, although the amounts needed for that purpose are not known.

The term “orthomolecular psychiatry” was coined by Linus Pauling in 1968 to refer to the treatment of psychiatric illnesses with substances (such as vitamins) that are normally present in the body. In orthomolecular psychiatry, high amounts of vitamins are sometimes used, not to correct a deficiency per se, but to create a more optimal biochemical environment. The mainstay of the orthomolecular approach to schizophrenia is niacin or niacinamide (vitamin B3) in high amounts. In early double-blind trials, 3 grams of niacin daily resulted in a doubling of the recovery rate, a 50% reduction in hospitalization rates, and a dramatic reduction in suicide rates.⁴¹ In a preliminary trial, some schizophrenic patients continued a course of vitamins (4 to 10 grams of niacin or niacinamide, 4 grams of vitamin C, and 50 mg or more of vitamin B6) after being discharged from the hospital, while another group of patients discontinued the vitamins upon discharge. Both groups continued to take their psychiatric medications. Those who continued to take the vitamins had a 50% lower re-admission rate compared with those who did not.⁴¹ Several later double-blind trials, including trials undertaken by the Canadian Mental Health Association, have been unable to reproduce these positive results.^43,44 Early supporters of niacin therapy contend that many of these trials were poorly designed.⁴⁵ One clinical trial reported no greater improvement in a group of schizophrenic patients given 6 grams of niacin than in others given 3 mg of niacin; all patients were also being treated with psychiatric medications.⁴⁶

There are potential side-effects of niacin therapy, including an uncomfortable flushing sensation, dermatitis (skin inflammation), heartburn, aggravation of peptic ulcers, increased blood sugar, increased panic and anxiety, and elevation of liver enzymes, which may indicate damage to liver cells. A positive side effect of niacin therapy is reduction of cholesterol levels. Some of these effects, such as flushing, gastric upset, and reduction of serum cholesterol, do not occur with the use of niacinamide.⁴⁷ Because of the seriousness of some of these side effects, high amounts of niacin should not be used without the supervision of a healthcare practitioner.

Vitamin B6 has been used in combination with niacin in the orthomolecular approach to schizophrenia. Pioneers of orthomolecular medicine reported benefits from this combination. However, although two placebo-controlled trials found significant improvement when schizophrenic patients were given either 3 grams of niacin or 75 mg of pyridoxine along with their psychiatric medications, this improvement was lost when the two vitamins were combined.^48,49 In a double-blind trial, schizophrenic patients were given either a vitamin program based on their individual laboratory tests or a placebo (25 mg of vitamin C) in addition to their psychiatric medications. The vitamin program included large amounts of various B vitamins, as well as vitamin C and vitamin E. After five months, the number of patients who improved was not different in the vitamin group compared with the placebo group.⁵⁰

Clinical trials of the effects of vitamin B6 have yielded differing results. The results of supplementation with 100 mg daily in one schizophrenic patient included dramatic reduction in side effects from medication, as well as reduction in schizophrenic symptoms.⁵¹ In a preliminary trial, 60 mg per day of vitamin B6 resulted in symptomatic improvement in only 5% of schizophrenic patients after four weeks.⁵² Another preliminary trial, however, found that a higher amount of vitamin B6—50 mg three times daily given for eight to twelve weeks—in addition to psychiatric medications, did bring about significant improvements in schizophrenic patients. These patients experienced a better sense of well-being, increased motivation, and greater interest in their “personal habits and their environment.”⁵³

Niacinamide (a form of vitamin B3) has been shown in animals to work in the brain in ways similar to drugs such as benzodiazepines (Valium-type drugs), which are used to treat anxiety.⁵³ One study found that niacinamide (not niacin) helped people get through withdrawal from benzodiazepines—a common problem.⁵⁴ A reasonable amount of niacinamide to take for anxiety, according to some doctors, is up to 500 mg four times per day.

Niacinamide (a form of vitamin B3) has been shown in animals to work in the brain in ways similar to drugs such as benzodiazepines (Valium-type drugs), which are used to treat anxiety.⁵⁵ One study found that niacinamide (not niacin) helped people get through withdrawal from benzodiazepines—a common problem.⁵⁶ A reasonable amount of niacinamide to take for anxiety, according to some doctors, is up to 500 mg four times per day.

Preliminary data indicate that vitamin B3 (niacin) supplementation may decrease thyroid hormone levels. In one small study, 2.6 grams of niacin per day helped lower blood fat levels.⁵⁷ After a year or more, thyroid hormone levels had fallen significantly in each person, although none experienced symptoms of hypothyroidism. In another case report, thyroid hormone levels decreased in two people who were taking niacin for high cholesterol and triglycerides; one of these two was diagnosed with hypothyroidism.⁵⁸ When the niacin was discontinued for one month, thyroid hormone levels returned to normal.

People with low blood levels of antioxidants and those who eat few antioxidant-rich fruits and vegetables have been reported to be at high risk for cataracts.^59,60

Vitamin B2 and vitamin B3 are needed to protect glutathione, an important antioxidant in the eye. Vitamin B2 deficiency has been linked to cataracts.^61,62 Older people taking 3 mg of vitamin B2 and 40 mg of vitamin B3 per day were partly protected against cataracts in one trial.⁶³ However, the intake of vitamin B2 in China is relatively low, and it is not clear whether supplementation would help prevent cataracts in populations where vitamin B2 intake is higher.

Preliminary observations suggest a possible role for vitamin B3 in HIV prevention and treatment.⁶⁴ A form of vitamin B3 (niacinamide) has been shown to inhibit HIV in test tube studies.⁶⁵ However, no published data have shown vitamin B3 to inhibit HIV in animals or in people. One study did show that HIV-positive people who consume more than 64 mg of vitamin B3 per day have a decreased risk of progression to AIDS or AIDS-related death.^66,66 Clinical trials in humans are required to validate these preliminary observations.

Niacinamide, a form of vitamin B3, can reduce the formation of a kynurenic acid—a substance that has been linked to photosensitivity. One trial studied the effects of niacinamide in people who had polymorphous light eruption.⁶⁷ While taking one gram three times per day, most people remained free of problems, despite exposure to the sun. Because of the potential for adverse effects, people taking this much niacinamide should do so only under medical supervision.