Overview
Vitamin B3 is required for the proper function of more than fifty enzymes. Without it, the body would not be able to release energy or make fats from carbohydrates. Vitamin B3 is also used to make sex hormones and other important chemical signal molecules.
Vitamin B3 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.
Requirements and Sources
The official U.S. and Canadian recommendations for daily intake of niacin are as follows:
Infants aged 0 to 6 months (2 mg) and 7 to 12 months (4 mg); children aged 1 to 3 years (6 mg), 4 to 8 years (8 mg), and 9 to 13 years (12 mg); males aged 14 years and older (14 mg); females aged 14 and older (14 mg); pregnant women (18 mg); and nursing women (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, such as meat, poultry, dairy products, and fish. Turkey and milk are particularly excellent sources of tryptophan.
Therapeutic Dosages
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 grams (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 of niacin. Inositol hexaniacinate may also cause less flushing than plain niacin, and if aspirin is taken along with niacin, the flushing reaction will usually decrease.
Therapeutic Uses
There is no question that niacin (but not niacinamide) can significantly improve cholesterol profile, reducing levels of total and low-density lipoprotien (LDL, or bad) cholesterol and raising high-density lipoprotein (HDL, or 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.
Niacinamide may improve blood sugar control in both children and adults who already have diabetes. In addition, some evidence has suggested that regular use of niacinamide (but not niacin) might help prevent diabetes in children at special risk of developing it; however, subsequent studies indicate that it probably does not work.
Preliminary evidence suggests that niacinamide may be able to decrease symptoms of osteoarthritis and help control polymorphous light eruption, a type of photosensitivity. Somewhat surprisingly, topical niacinamide has shown some promise for skin conditions. In a double-blind study of fifty women with signs of aging skin, use of a niacinamide cream significantly improved skin appearance and elasticity compared with placebo cream. Niacinamide cream has also shown promise for rosacea.
The inositol hexaniacinate form of niacin (taken orally) may be helpful for intermittent claudication14 and Raynaud’s phenomenon. In addition, weak and in some cases contradictory evidence suggests one of the several forms of niacin might be helpful for people with bursitis, cataracts, human immunodeficiency virus (HIV) infection, pregnancy, schizophrenia, and tardive dyskinesia.
A new use of niacin was reported in 2007: It appears that some people take very high doses of niacin (about 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, but also, 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.
Scientific Evidence
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.
High cholesterol/triglycerides. Niacin has been used since the 1950s to improve cholesterol profile. Several well-designed double-blind, placebo-controlled studies have found that niacin can reduce LDL (bad) cholesterol by approximately 10 percent and triglycerides by 25 percent, while raising HDL (good) cholesterol by 20 to 30 percent. Niacin also lowers levels of lipoprotein(a)–another risk factor for atherosclerosis–by about 35 percent. Long-term studies have shown that use of niacin can significantly reduce death rates from cardiovascular disease. Niacin also appears to be a safe and effective treatment for high cholesterol in people with diabetes and, contrary to previous reports, does not seem to raise blood sugar levels.
Treating diabetes
. 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 antioxidant 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 diabetes, but it did not use a double-blind design.
Intermittent claudication
. Double-blind studies involving a total of about four hundred individuals have found that inositol hexaniacinate can improve walking distance for people with intermittent claudication. For example, in one study, one hundred individuals were given either placebo or 4 g of inositol hexaniacinate daily. Over a period of three months, participants improved significantly in the number of steps they could take on a special device before experiencing excessive pain.
Osteoarthritis
. There is some evidence that niacinamide may provide some benefits for those with osteoarthritis. In a double-blind study, seventy-two people with arthritis were given either 3,000 milligrams (mg) daily of niacinamide in six equal doses or placebo for twelve weeks. The results showed that treated participants experienced a 29 percent improvement in symptoms, whereas those given placebo worsened by 10 percent. However, at this dose, liver inflammation is a concern that must be taken seriously.
Raynaud’s phenomenon
. According to one small double-blind study, the inositol hexaniacinate form of niacin may be helpful for Raynaud’s phenomenon. The dosage used was 4 g daily—once again, a dosage high enough for liver inflammation to be a real possibility.
Safety Issues
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 percent 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 manufacturers’ Web sites, there is no reliable evidence that inositol hexaniacinate is safer than ordinary niacin.
As noted above, a single dose of 2.5 to 5 g 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.
People who have liver disease, ulcers (presently or in the past), or gout, or drink too much alcohol should 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. However, 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 carbamazepine and primidone. Niacinamide might increase blood levels of these drugs, possibly requiring reduction in drug dosage. People should 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 eighteen years old or younger).
Important Interactions
For people who are taking cholesterol-lowering drugs in the statin family, niacin might offer potential benefits; however, there are real dangers to this combination. People should not try it except under physician supervision.
People taking the antituberculosis drug isoniazid (INH) may need extra niacin. People who take anticonvulsant drugs, such as carbamazepine or primidone, should not take niacinamide except under physician supervision. Similarly, people who drink alcohol excessively should not take niacin except under physician supervision.
Bibliography
Bissett, D. L., et al. “Niacinamide: A B Vitamin That Improves Aging Facial Skin Appearance.” Dermatological Surgery 31 (2005): 860-865.
Cabrera-Rode, E., et al. “Effect of Standard Nicotinamide in the Prevention of Type 1 Diabetes in First Degree Relatives of Persons with Type 1 Diabetes.” Autoimmunity 39 (2006): 333-340.
Crino, A., et al. “A Randomized Trial of Nicotinamide and Vitamin E in Children with Recent Onset Type 1 Diabetes (IMDIAB IX).” European Journal of Endocrinology 150 (2004): 719-724.
Draelos, Z. D., et al. “Niacinamide-Containing Facial Moisturizer Improves Skin Barrier and Benefits Subjects with Rosacea.” Cutis: Cutaneous Medicine for the Practitioner 76 (2005): 135-141.
Gale, E. A., et al. “European Nicotinamide Diabetes Intervention Trial (ENDIT): A Randomised Controlled Trial of Intervention Before the Onset of Type 1 Diabetes.” The Lancet 363 (2004): 925-931.
Goldberg, R. B., and T. A. Jacobson. “Effects of Niacin on Glucose Control in Patients with Dyslipidemia.” Mayo Clinic Proceedings 83 (2008): 470-478.
Grundy, S. M., et al. “Efficacy, Safety, and Tolerability of Once-Daily Niacin for the Treatment of Dyslipidemia Associated with Type 2 Diabetes: Results of the Assessment of Diabetes Control and Evaluation of the Efficacy of Niaspan Trial.” Archives of Internal Medicine 162 (2002): 1568-1576.
Mittal, M. K., et al. “Toxicity from the Use of Niacin to Beat Urine Drug Screening.” Annals of Emergency Medicine 50, no. 5 (2007): 587-590.
Wink, J., G. Giacoppe, and J. King. “Effect of Very-Low-Dose Niacin on High-Density Lipoprotein in Patients Undergoing Long-Term Statin Therapy.” American Heart Journal 143 (2002): 514-518.
Wolfe, M. L., et al. “Safety and Effectiveness of Niaspan When Added Sequentially to a Statin for Treatment of Dyslipidemia.” American Journal of Cardiology 87 (2001): 476-479.
No comments:
Post a Comment