Niacin, also known as vitamin B3, is an essential nutrient required for the synthesis of nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+). These redox cofactors are central to cellular energy production, mitochondrial function, DNA repair signaling, and numerous metabolic pathways. Because humans cannot synthesize adequate amounts of niacin de novo, dietary intake is required. Clinically significant deficiency leads to pellagra, a syndrome classically characterized by dermatitis, diarrhea, and neuropsychiatric manifestations, often summarized as the “three D’s.” In contemporary practice, milder insufficiency can present more subtly with fatigue, reduced exercise tolerance, cognitive changes, and skin abnormalities that may be mistaken for dermatologic or gastrointestinal disorders.
Mechanistically, niacin is converted in the body to NAD+ and NADP+, which function as electron carriers. During glycolysis and oxidative phosphorylation, NAD+ cycles between oxidized and reduced forms to accept and donate electrons, enabling efficient ATP generation. Reduced NAD+ availability can impair energy metabolism, contribute to mitochondrial dysfunction, and shift cellular redox balance, which may worsen inflammatory signaling. NAD+ also supports metabolic flexibility and influences pathways involved in fatty acid oxidation and glucose utilization, so deficiency may manifest as generalized weakness, reduced endurance, and non-specific malaise.
Niacin’s role in skin integrity is partly mediated through its effects on keratinocyte differentiation, barrier maintenance, and regulation of oxidative stress. NADPH-dependent reactions are particularly relevant to antioxidant defense, including the regeneration of reduced glutathione. When niacin status is low, impaired redox buffering can increase susceptibility to inflammatory skin reactions, leading to photosensitive dermatitis typical of pellagra. Lesions often occur in sun-exposed areas and may progress to hyperpigmentation, erythema, and scaling, reflecting disrupted epidermal homeostasis.
Gastrointestinal symptoms such as diarrhea are also plausibly linked to niacin-related effects on mucosal energy metabolism and epithelial turnover. Rapidly dividing tissues, including intestinal epithelium and immune cells, require robust NAD(P) cofactor availability. Deficiency can therefore compromise normal repair processes and barrier function, contributing to malabsorption-like presentations or inflammatory diarrhea.
Neuropsychiatric manifestations are among the most clinically important aspects of niacin deficiency. Although the exact neurobiology is multifactorial, reduced NAD+ can impair neuronal energy demand, synaptic function, and neurotransmission through downstream metabolic effects. Patients may experience irritability, depression-like symptoms, confusion, and, in severe cases, delirium. Cognitive changes can coexist with mood alterations, and severe deficiency can progress to marked encephalopathy.
Dietary sources of niacin include both animal and plant foods. Animal proteins such as poultry, fish, and meat contain niacin in more bioavailable forms (including preformed niacin). Plant-based options can contribute as well, but bioavailability may vary due to food matrix effects and the presence of niacin-bound forms. Some plants also provide tryptophan, an essential amino acid that can be converted to niacin via the kynurenine pathway, though conversion efficiency depends on overall nutritional status, liver function, and adequate availability of cofactors such as vitamin B6. Therefore, individuals with restricted diets, malabsorption syndromes, alcoholism, or chronic inflammatory conditions may be at increased risk of insufficient niacin.
Restoring healthy niacin status requires evaluation of the dietary pattern and underlying causes. In confirmed or strongly suspected deficiency, clinicians may recommend niacin or niacinamide supplementation depending on the clinical goal and patient risk profile. For pellagra, treatment typically results in rapid improvement when deficiency is corrected; skin lesions may respond over days to weeks, while neurologic and gastrointestinal symptoms may take longer to normalize. However, supplementation should be medically guided because high-dose niacin can cause adverse effects, including flushing, pruritus, gastrointestinal discomfort, and, at higher doses, hepatotoxicity and worsening insulin resistance. Formulations used for dyslipidemia can differ in risk and dose; this is not the same as nutritional replacement for deficiency.
If symptoms like dermatitis, persistent diarrhea, fatigue, or mood/cognitive changes are present, a structured assessment is recommended. History should include diet quality, weight loss, alcohol use, gastrointestinal disorders, medications that affect absorption or metabolism, and symptoms of broader vitamin deficiencies (e.g., riboflavin or B6). Laboratory evaluation may include nutritional markers and targeted testing guided by clinician judgment, particularly when symptoms are severe or progressive. Differential diagnoses may include contact dermatitis, celiac disease, inflammatory bowel disease, depression, other nutritional deficiencies, and metabolic or neurologic conditions.
In summary, niacin is indispensable for NAD+/NADP+-dependent energy metabolism, redox regulation, and tissue maintenance. Deficiency can produce pellagra-spectrum manifestations involving skin, gastrointestinal function, and neuropsychiatric health. Appropriate dietary strategies and, when indicated, supervised supplementation can restore biochemical function and improve clinical outcomes. Source: [Creator/Source].
Dr. Eric Berg DC: Niacin is key for energy, skin health & brain function. Low levels can cause symptoms like dermatitis, diarrhea, fatigue & mood changes. Animal protein is the best source, with some plant options too. See how to restore healthy levels. Dr. Eric Berg,. #breaking
— @dr_ericberg May 1, 2026
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