This can be a reality sheet meant for well being professionals. For a reader-friendly overview of Niacin, see our shopper reality sheet on Niacin.
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Introduction
Niacin (also referred to as vitamin B3) is without doubt one of the water-soluble B nutritional vitamins. Niacin is the generic title for nicotinic acid (pyridine-3-carboxylic acid), nicotinamide (niacinamide or pyridine-3-carboxamide), and associated derivatives, similar to nicotinamide riboside [1-3]. Niacin is of course current in lots of meals, added to some meals merchandise, and out there as a dietary complement.
All tissues within the physique convert absorbed niacin into its predominant metabolically energetic kind, the coenzyme nicotinamide adenine dinucleotide (NAD). Greater than 400 enzymes require NAD to catalyze reactions within the physique, which is greater than for every other vitamin-derived coenzyme [1]. NAD can also be transformed into one other energetic kind, the coenzyme nicotinamide adenine dinucleotide phosphate (NADP), in all tissues besides skeletal muscle [4].
NAD and NADP are required in most metabolic redox processes in cells the place substrates are oxidized or decreased. NAD is primarily concerned in catabolic reactions that switch the potential power in carbohydrates, fat, and proteins to adenosine triphosphate (ATP), the cell’s main power forex [4]. NAD can also be required for enzymes concerned in crucial mobile features, similar to the upkeep of genome integrity, management of gene expression, and mobile communication [3,4]. NADP, in distinction, allows anabolic reactions, such because the synthesis of ldl cholesterol and fatty acids, and performs a citical function in sustaining mobile antioxidant operate.
Most dietary niacin is within the type of nicotinic acid and nicotinamide, however some meals include small quantities of NAD and NADP. The physique additionally converts some tryptophan, an amino acid in protein, to NAD, so tryptophan is taken into account a dietary supply of niacin.
When NAD and NADP are consumed in meals, they’re transformed to nicotinamide within the intestine after which absorbed [4]. Ingested niacin is absorbed primarily within the small gut, however some is absorbed within the abdomen [1-3].
Even when taken in very excessive doses of three–4 g, niacin is sort of fully absorbed. As soon as absorbed, physiologic quantities of niacin are metabolized to NAD. Some extra niacin is taken up by purple blood cells to kind a circulating reserve pool. The liver methylates any remaining extra to N1-methyl-nicotinamide, N1-methyl-2-pyridone-5-carboxamide, and different pyridone oxidation merchandise, that are then excreted within the urine. Unmetabolized nicotinic acid and nicotinamide is perhaps current within the urine as nicely when niacin intakes are very excessive.
Ranges of niacin within the blood are usually not dependable indicators of niacin standing. Essentially the most delicate and dependable measure of niacin standing is the urinary excretion of its two main methylated metabolites, N1-methyl-nicotinamide and N1-methyl-2-pyridone-5-carboxamide [2]. Excretion charges in adults of greater than 17.5 micromol/day of those two metabolites mirror sufficient niacin standing, whereas excretion charges between 5.8 and 17.5 micromol/day mirror low niacin standing. An grownup has poor niacin standing when urinary-excretion charges are lower than 5.8 micromol/day. Indicators of inadequacy similar to this and different biochemical indicators (e.g., a 2-pyridone oxidation product of N1-methyl-nicotinamide under detection limits in plasma or low erythrocyte NAD concentrations) happen nicely earlier than overt scientific indicators of deficiency [2]. One other measure of niacin standing takes into consideration the truth that NAD ranges decline as niacin standing deteriorates, whereas NADP ranges stay comparatively fixed [1,3,5]. A “niacin number” (the ratio of NAD to NADP concentrations in complete blood x 100) under 130 suggests niacin deficiency [6,7]. A “niacin index” (the ratio of erythrocyte NAD to NADP concentrations) under 1 means that a person is vulnerable to creating niacin deficiency [8]. No purposeful biochemical assessments that mirror complete physique shops of niacin can be found [5].
Beneficial Intakes
Consumption suggestions for niacin and different vitamins are supplied within the Dietary Reference Intakes (DRIs) developed by an knowledgeable committee of the Meals and Diet Board (FNB) on the Nationwide Academies of Sciences, Engineering, and Medication [2]. DRI is the final time period for a set of reference values used for planning and assessing nutrient intakes of wholesome folks. These values, which differ by age and intercourse, embrace:
Desk 1 lists the present RDAs for niacin as mg of niacin equivalents (NE) [2]. The FNB defines 1 NE as 1 mg niacin or 60 mg of the amino acid tryptophan (which the physique can convert to niacin). Niacin RDAs for adults are based mostly on niacin metabolite excretion information. For youngsters and adolescents, niacin RDAs are extrapolated from grownup values on the idea of physique weight. The AI for infants from beginning to six months is for niacin alone, as younger infants use nearly all of the protein they devour for progress and growth; it’s equal to the imply consumption of niacin in wholesome, breastfed infants. For infants aged 7-12 months, the AI for niacin is in mg NE and is predicated on quantities consumed from breast milk and stable meals.
* Ample Consumption
Sources of Niacin – “vitamin b3 food”
Meals
Niacin is current in all kinds of meals. Many animal-based meals—together with poultry, beef, and fish—present about 5-10 mg niacin per serving, primarily within the extremely bioavailable types of NAD and NADP [3]. Plant-based meals, similar to nuts, legumes, and grains, present about 2-5 mg niacin per serving, primarily as nicotinic acid. In some grain merchandise, nevertheless, naturally current niacin is basically sure to polysaccharides and glycopeptides that make it solely about 30% bioavailable [3,4]. Many breads, cereals, and toddler formulation in america and lots of different nations include added niacin. Niacin that’s added to enriched and fortified meals is in its free kind and due to this fact extremely bioavailable [2].
Tryptophan is one other meals supply of niacin as a result of this amino acid—when current in quantities past that required for protein synthesis—may be transformed to NAD, primarily within the liver [3,5]. Essentially the most generally used estimate of effectivity for tryptophan conversion to NAD is 1:60 (i.e., 1 mg niacin [NAD] from 60 mg tryptophan). Turkey is an instance of a meals excessive in tryptophan; a 3-oz portion of turkey breast meat gives about 180 mg tryptophan, which might be equal to three mg niacin [9]. Nevertheless, the effectivity of the conversion of tryptophan to NAD varies significantly in numerous folks [3].
Desk 2 lists a number of meals sources of niacin.
* These values are for the niacin content material of meals solely. They don’t embrace the contribution of tryptophan, a few of which is transformed to NAD within the physique.
** DV = Day by day Worth. The U.S. Meals and Drug Administration (FDA) developed DVs to assist customers evaluate the nutrient contents of meals and dietary dietary supplements inside the context of a complete food plan. The DV for niacin is 16 mg for adults and youngsters aged 4 years and older [10]. The FDA doesn’t require meals labels to listing niacin content material except niacin has been added to the meals. Meals offering 20% of extra of the DV are thought of to be excessive sources of a nutrient.
The U.S. Division of Agriculture’s (USDA’s) FoodData Central lists the nutrient content material of many meals and gives a complete listing of meals containing niacin organized by nutrient content material.
Dietary dietary supplements
Niacin is out there in multivitamin-mineral merchandise, in dietary supplements containing different B-complex nutritional vitamins, and in dietary supplements containing niacin solely. Nicotinic acid and nicotinamide are the 2 commonest types of niacin in dietary supplements. Some niacin-only dietary supplements include 500 mg or extra per serving, which is way larger than the RDA for this nutrient [11].
Nicotinic acid in supplemental quantities past dietary wants may cause pores and skin flushing, so some formulations are manufactured and labeled as extended, sustained, prolonged, or timed launch to reduce this disagreeable aspect impact. Nicotinamide doesn’t produce pores and skin flushing due to its barely completely different chemical construction [2,12]. Niacin dietary supplements are additionally out there within the type of inositol hexanicotinate, and these dietary supplements are steadily labeled as being “flush free” as a result of they don’t trigger flushing. The absorption of niacin from inositol hexanicotinate varies extensively however on common is 30% decrease than from nicotinic acid or nicotinamide, that are nearly fully absorbed [12-14]. A niacin-like compound, nicotinamide riboside, can also be out there as a dietary complement, however it’s not marketed or labelled as a supply of niacin [11].
Niaspan® and generic niacin ER, out there as a prescription medication, gives 500-1,000 mg extended-release nicotinic acid. It’s used to deal with excessive blood levels of cholesterol.
Niacin Intakes and Standing
Most individuals in america devour greater than the RDA for niacin. An evaluation of information from the 2015–2016 Nationwide Well being and Diet Examination Survey (NHANES) discovered that the typical every day niacin consumption from meals and drinks was 21.4 mg for ages 2–19 [15]. In adults, the typical every day niacin consumption from meals and drinks was 31.4 mg in males and 21.3 mg in ladies. An evaluation of information from the 2009-2012 NHANES discovered that only one% of adults had intakes of niacin from meals and drinks under the EAR [16]. Amongst all racial and ethnic teams, Hispanics had the best prevalence, 1.3%, of niacin intakes under the EAR [17].
Based on self-reported information from the 2013-2014 NHANES, 21% of all people aged 2 and older took a dietary complement containing niacin [15]. The proportion of customers elevated with age from 8% of these aged 12-19 years to 39% of males and 40% of girls aged 60 and older. Complement use doubled or tripled complete niacin intakes in contrast with intakes from food plan alone. Based on information from the 2003-2006 NHANES, 10% of all people aged 2 and older who took dietary dietary supplements had complete niacin intakes that reached or exceeded the UL [18].
Niacin Deficiency
Extreme niacin deficiency results in pellagra, a illness characterised by a pigmented rash or brown discoloration on pores and skin uncovered to daylight; the pores and skin additionally develops a roughened, sunburned-like look [2,4,19,20]. As well as, pellagra may cause a brilliant purple tongue and modifications within the digestive tract that result in vomiting, constipation, or diarrhea. The neurological signs of pellagra can embrace despair; apathy; headache; fatigue; lack of reminiscence that may progress to aggressive, paranoid, and suicidal behaviors; and auditory and visible hallucinations [2-4]. As pellagra progresses, anorexia develops, and the affected person finally dies [3].
Pellagra is unusual in industrialized populations and is usually restricted to folks residing in poverty, similar to refugees and displaced individuals who eat very restricted diets low in niacin and protein [20,21]. Pellagra was not unusual within the early twentieth century amongst people residing in poverty within the southern United States and elements of Europe whose restricted diets consisted primarily of corn [2,3]. The World Well being Group recommends treating pellagra with 300 mg/day nicotinamide in divided doses for 3-4 weeks together with a B-complex or yeast product to deal with probably deficiencies in different B nutritional vitamins [20].
Though frank niacin deficiencies resulting in pellagra are very uncommon in america, some people have marginal or low niacin standing [2,19,21,22].