Summary of Niacin Effects

• Niacin and its derivative nicotinamide are dietary precursors of nicotinamide adenine dinucleotide (NAD), which can be phosphorylated (NADP) and reduced (NADH and NADPH). NAD functions in oxidation-reduction (redox) reactions and non-redox reactions. 
• Pellagra is the disease of severe niacin deficiency. It is characterized by symptoms affecting the skin, the digestive system, and the nervous system and can lead to death if left untreated.
• Dietary tryptophan can be converted to niacin, although the efficiency of conversion is low in humans and affected by deficiencies in other nutrients. 
• Causes of niacin deficiency include inadequate oral intake, poor bioavailability from unlimed grains, defective tryptophan absorption, metabolic disorders, and the long-term use of chemotherapeutic treatments. 
• The requirements for niacin are based on the urinary excretion of niacin metabolites. 
• NAD is the sole substrate for PARP enzymes involved in DNA repair activity in response to DNA strand breaks; thus, NAD is critical for genome stability. Several studies, mostly using in vitro and animal models, suggest a possible role for niacin in cancer prevention. Nevertheless, large studies are needed to investigate the association between niacin deficiency and cancer risk in human populations. 
• Despite promising initial results, nicotinamide administration has failed to prevent or delay the onset of type 1 diabetes in high-risk relatives of type 1 diabetics. Future research might explore the use of nicotinamide in combined therapy and evaluate activators of NAD-dependent enzymes. 
• At pharmacologic doses, niacin, but not nicotinamide, improves the lipid profile and reduces coronary events and total mortality in patients at high risk for coronary heart disease. Several clinical trials have explored the cardiovascular benefit of niacin in combination with other lipid-lowering medications. 
• Elevated tryptophan breakdown and niacin deficiency have been reported in HIV-positive people. This population is also at high risk for cardiovascular disease, and current data show that they could benefit from niacin supplementation. 
• The tolerable upper intake level (UL) for niacin is based on skin flushing, niacin's most prominent side effect. A new drug, laropiprant, has been developed to reduce skin flushing. Adverse effects have also been reported with pharmacologic doses of niacin administrated alone or in combination with other lipid-lowering medications. 

Niacin is a water-soluble vitamin, which is also known as nicotinic acid or vitamin B3. Nicotinamide is the derivative of niacin and used by the body to form the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP).