Vitamin B3 (niacin)
A B vitamin essential for energy metabolism and for the coenzymes NAD and NADP that run hundreds of reactions in every cell. Severe deficiency causes pellagra — the classic 'three D's' of dermatitis, diarrhoea and dementia. It is rarely measured directly and is usually a clinical diagnosis.
What it measures
Niacin (vitamin B3, which includes nicotinic acid and nicotinamide) is a water-soluble B vitamin that the body uses to make NAD and NADP — coenzymes that are central to energy production and to hundreds of reactions across metabolism, DNA repair and cell signalling. The body can also make some niacin from the amino acid tryptophan, so both dietary niacin and protein intake matter. It is found in meat, fish, poultry, peanuts, legumes and fortified grains. Because stores are limited, sustained poor intake leads to deficiency, whose severe form is pellagra — historically seen where maize-based diets predominated (maize niacin is poorly absorbed). Pellagra is remembered by the 'three D's': dermatitis (a sun-exposed, symmetrical, pigmented rash), diarrhoea, and dementia (confusion, memory and mood changes), progressing to death if untreated ('the fourth D'). Modern deficiency is uncommon but seen with alcohol dependence, malabsorption, some rare genetic conditions (Hartnup disease, carcinoid syndrome) and severe malnutrition. Niacin is seldom measured as a blood level; deficiency is usually recognised clinically, and status can be checked with urinary niacin metabolites. Separately, high-dose niacin has been used as a medication for cholesterol.
What a high value can mean
- Supplements or niacin medication — high-dose niacin (used for cholesterol) is the usual reason; it can cause facial flushing, and at high doses affect the liver and blood sugar.
- A high dietary/blood level is otherwise not clinically important — excess is passed in the urine.
What a low value can mean
- Dietary deficiency — poor intake, especially maize-heavy diets low in other protein.
- Alcohol dependence — a leading cause of pellagra today.
- Malabsorption — gut conditions reducing uptake.
- Rare metabolic disorders — Hartnup disease (reduced tryptophan uptake), carcinoid syndrome (tryptophan diverted).
- Severe malnutrition or restricted diets.
When to discuss with a doctor
Niacin is rarely tested directly; a deficiency is usually recognised clinically from the pellagra picture — a symmetrical, sun-exposed rash, diarrhoea and changes in memory or mood — especially in someone with alcohol dependence, malabsorption or a very poor diet. Pellagra responds dramatically and quickly to niacin replacement, so recognising the pattern matters. Because B-vitamin deficiencies cluster, it is usually treated alongside a look at the wider B-vitamin and nutritional picture. Mediora.AI can surface a low niacin, or the associated skin, gut and neurological features, alongside the other B vitamins so the deficiency pattern is visible; confirming pellagra and starting treatment belongs with your doctor, and severe or rapidly progressing symptoms need prompt care.