| Therapeutic Dosages
| Therapeutic Uses
What Is the Scientific Evidence for Vitamin B
| Safety Issues
| Interactions You Should Know About
is required for the proper function of more than 50 enzymes. Without it, your body would not be able to release energy or make fats from carbohydrates. Vitamin B
is also used to make sex hormones and other important chemical signal molecules.
comes in two principal forms: niacin (nicotinic acid) and niacinamide (nicotinamide). When taken in low doses for nutritional purposes, these two forms of the vitamin are essentially identical. However, each has its own particular effects when taken in high doses. Additionally, a special form of niacin called inositol hexaniacinate has shown some promise as a treatment with special properties of its own.
The official US and Canadian recommendations for daily intake of niacin are as follows:
- 0-6 months: 2 mg
- 7-12 months: 4 mg
- 1-3 years: 6 mg
- 4-8 years: 8 mg
- 9-13 years: 12 mg
- 14 years and older: 16 mg
- 14 years and older: 14 mg
: 18 mg
: 17 mg
Because the body can make niacin from the common amino acid tryptophan, niacin deficiencies are rare in developed countries. However, the antituberculosis drug isoniazid (INH) impairs the body's ability to produce niacin from tryptophan and may create symptoms of niacin deficiency.
Good food sources of niacin are seeds, yeast, bran, peanuts (especially with skins), wild rice, brown rice, whole wheat, barley, almonds, and peas. Tryptophan is found in protein foods (meat, poultry, dairy products, fish). Turkey and milk are particularly excellent sources of tryptophan.
When used as therapy for a specific disease, niacin, niacinamide, and inositol hexaniacinate are taken in dosages much higher than nutritional needs, about 1 to 4 g daily. Because of the risk of liver inflammation at these doses, medical supervision is essential.
Many people experience an unpleasant flushing sensation and headache when they take niacin. These symptoms can usually be reduced by gradually increasing the dosage over several weeks or by using slow-release niacin. However, slow-release niacin appears to be more likely to cause liver inflammation than other forms. Inositol hexaniacinate may also cause less flushing than plain niacin, and if you take an aspirin along with niacin, the flushing reaction will usually decrease.
There is no question that niacin (but not niacinamide) can significantly improve
profile, reducing levels of total and LDL ("bad") cholesterol and raising HDL ("good") cholesterol.
However, unpleasant flushing reactions as well as a risk of liver inflammation and dangerous interactions with other cholesterol-lowering drugs have kept niacin from being widely used (see
Niacinamide may improve blood sugar control in both children and adults who already have diabetes.
In addition, some evidence had suggested that regular use of niacinamide (but not niacin) might help
in children at special risk of developing it;
unfortunately, subsequent studies indicate that it probably does not work.
Preliminary evidence suggests that niacinamide may be able to decrease symptoms of
and help control polymorphous light eruption, a type of
niacinamide has shown some promise for skin conditions. In a double-blind study of 50 women with signs of
, use of a niacinamide cream significantly improved skin appearance and elasticity as compared to placebo cream.
Niacinamide cream has also shown promise for
The inositol hexaniacinate form of niacin (taken orally) may be helpful for
In addition, weak and in some cases contradictory evidence suggests one of the several forms of niacin might be helpful for people with
A new use of niacin was reported in 2007: it appears that some people take very high doses of niacin (in the neighborhood of 2.5 to 5 grams at a time ) in the belief that it will mask drugs in the urine.
However, not only does niacin fail to conceal the presence of drugs on a urine drug screen, when taken suddenly at doses this high, niacin can cause life-threatening problems involving the liver and heart. In addition, it can dangerously disturb blood sugar regulation and blood coagulation.
What Is the Scientific Evidence for Vitamin B
Niacin is one of the best researched of all the vitamins, and the evidence for using it to treat at least one condition—high cholesterol—is strong enough that it has become an accepted mainstream treatment.
Niacin has been used since the 1950s to improve
profile. Several well-designed
studies have found that niacin can reduce LDL ("bad") cholesterol by approximately 10% and triglycerides by 25% while raising HDL ("good") cholesterol by 20% to 30%.
Niacin also lowers levels of lipoprotein(a)—another risk factor for atherosclerosis—by about 35%. Long-term studies have shown that use of niacin can significantly reduce death rates from cardiovascular disease.
Niacin appears to be a safe and effective treatment for high cholesterol in people with diabetes as well, and (contrary to previous reports) does not seem to raise blood sugar levels.
When a child develops diabetes, there is an interval called the honeymoon period in which the pancreas can still make some insulin and there is little to no need for injected insulin. Weak evidence suggests that niacinamide might slightly delay the onset of more severe symptoms.
A cocktail of niacinamide plus
vitamins and minerals has also been tried, but the results were disappointing in one study.
However, in another study, use of intensive insulin therapy along with niacinamide and vitamin E was more effective than insulin plus niacinamide alone in prolonging the honeymoon period.
A recent study suggests that niacinamide may also improve blood sugar control in type 2 (adult-onset) diabetes, but it did not use a double-blind design.
(For information on why this is important, see
Why Does This Database Rely on Double-blind Studies?
Double-blind studies involving a total of about 400 individuals have found that inositol hexaniacinate can improve walking distance for people with
For example, in one study, 100 individuals were given either placebo or 4 g of inositol hexaniacinate daily.
Over a period of 3 months, participants improved significantly in the number of steps they could take on a special device before experiencing excessive pain.
There is some evidence that niacinamide may provide some benefits for those with
. In a double-blind study, 72 people with arthritis were given either 3,000 mg daily of niacinamide (in 6 equal doses) or placebo for 12 weeks.
The results showed that treated participants experienced a 29% improvement in symptoms, whereas those given placebo worsened by 10%. However, at this dose, liver inflammation is a concern that must be taken seriously.
According to one small double-blind study, the inositol hexaniacinate form of niacin may be helpful for
The dosage used was 4 g daily—once again a dosage high enough for liver inflammation to be a real possibility.
When taken at a dosage of more than 100 mg daily, niacin frequently causes annoying skin flushing, especially in the face, as well as stomach distress, itching, and headache.
In studies, as many as 43% of individuals taking niacin quit because of unpleasant side effects.
A more dangerous effect of niacin is liver inflammation. Although some reports suggest that it occurs most commonly with slow-release niacin, it can occur with any type of niacin when taken at a daily dose of more than 500 mg (usually 3 g or more). Regular blood tests to evaluate liver function are, therefore, mandatory when using high-dose niacin (or niacinamide or inositol hexaniacinate). This reaction almost always goes away when niacin is stopped.
: Contrary to claims on some manufacturer's websites, there is no reliable evidence that inositol hexaniacinate is safer than ordinary niacin.
As noted above, a single dose of 2.5 to 5 grams of niacin (used in the vain hope of passing a urine drug test despite the presence of drugs in the system) can cause life-threatening disturbances in body function.
Since this range includes the high-end of the dosage used for treating cholesterol, presumably people who gradually work up to taking several grams of niacin daily can accommodate it in a way that those who take it suddenly cannot.
If you have liver disease, ulcers (presently or in the past), gout, or drink too much alcohol,
do not take high-dose niacin except on medical advice.
While there has been some concern that niacin may raise blood sugar levels in diabetics, the effect appears to be slight, and it carries little, if any, clinical significance.
Combining high-dose niacin with statin drugs (the most effective medications for high cholesterol) further improves cholesterol profile by raising HDL (“good”) cholesterol.
Unfortunately, there are real concerns that this combination therapy could cause a potentially fatal condition called rhabdomyolysis.
A growing body of evidence, however, suggests that the risk is relatively slight in individuals with healthy kidneys. Furthermore, even much lower doses of niacin than the usual dose given to improve cholesterol levels (100 mg versus 1,000 mg or more) may provide a similar benefit.
At this dose, the risk of rhabdomyolysis should be decreased.
Nonetheless, it is not safe to try this combination except under close physician supervision. Rhabdomyolysis can be fatal.
Another potential drug interaction involves the anticonvulsant drugs
. Niacinamide might increase blood levels of these drugs, possibly requiring reduction in drug dosage.
Do not use this combination except under physician supervision.
The maximum safe dosage of niacin for pregnant or nursing women has been set at 35 mg daily (30 mg if 18 years old or younger).
Interactions You Should Know About
If you are taking:
Cholesterol-lowering drugs in the
family, niacin might offer potential benefits; however, there are real dangers to this combination. Do not try it except under physician supervision.
The antituberculosis drug
: You may need extra niacin.
Anticonvulsant drugs such as
: Do not take niacinamide except under physician supervision.
If you drink
- Do not take niacin except under physician supervision.