Vitamin B3 is a water-soluble nutrient your body uses to convert food into energy, repair damaged DNA, and support hundreds of chemical reactions in your cells. It comes in two main forms found in food: niacin (nicotinic acid) and niacinamide (nicotinamide). Both forms ultimately produce the same essential molecule your cells need, called NAD, but they behave differently when taken in high doses. Adults need 14 to 16 mg per day, and most people eating a varied diet get enough without supplements.
What Vitamin B3 Does in Your Body
Nearly every cell in your body depends on vitamin B3. Once absorbed, it’s converted into two coenzymes: NAD and NADP. These aren’t just minor players. NAD works primarily in energy-producing reactions, breaking down carbohydrates, fats, proteins, and alcohol to fuel your cells. NADP handles the opposite job, helping your body build things like fatty acids, cholesterol, and hormones. NADP also helps regenerate your body’s antioxidant and detoxification systems.
Beyond energy, NAD is critical for keeping your DNA intact. When your DNA gets damaged (which happens routinely from sun exposure, normal metabolism, and environmental toxins), repair enzymes consume NAD as fuel to fix the breaks. NAD also powers a family of proteins called sirtuins that regulate gene activity, cell aging, and cell division. Without adequate B3, these repair processes slow down, leaving cells more vulnerable to damage over time.
Forms of Vitamin B3
The two dietary forms, niacin and niacinamide, both satisfy your daily B3 requirement. The practical difference shows up at high doses. Niacin causes a distinctive flushing reaction: warmth, redness, and tingling in the face and chest triggered by blood vessels rapidly dilating near the skin’s surface. Niacinamide does not cause this flush, which is why it’s the form most commonly used in supplements and skincare products.
Your body can also make its own B3 from tryptophan, an amino acid found in protein-rich foods. The conversion is inefficient: it takes roughly 60 mg of tryptophan to produce just 1 mg of niacin. This means protein-rich diets contribute some B3, but you still need direct dietary sources to meet your needs reliably.
How Much You Need Daily
The recommended daily intake for adults is 16 mg for men and 14 mg for women. During pregnancy, the recommendation rises to 18 mg, and during breastfeeding, 17 mg. Children’s needs scale with age, from 6 mg at ages 1 to 3 up to 12 mg by age 13. These values are expressed in “niacin equivalents,” which account for both the B3 in food and the small amount your body makes from tryptophan.
Best Food Sources
Vitamin B3 is widespread in the food supply. The richest sources are poultry, fish (especially tuna and salmon), beef, and pork. A single chicken breast can deliver more than your full daily requirement. Among plant foods, peanuts, mushrooms, green peas, and fortified grains and cereals are strong contributors. In the United States, enriched bread, flour, and cereal products have niacin added by law, which is one reason outright deficiency is rare in developed countries.
One historical quirk worth knowing: corn contains B3 in a chemically bound form that your body can’t absorb well. Populations that relied heavily on untreated corn as a staple once suffered widespread deficiency. Indigenous peoples in Central America solved this problem centuries ago through nixtamalization, a process of soaking corn in alkaline lime water that releases the bound niacin and makes it absorbable. Modern tortilla production still uses this technique. Processing corn this way does cause some B-vitamin losses (30 to 70% during lime cooking), but it makes the remaining niacin far more bioavailable than eating untreated corn.
What Happens When You Don’t Get Enough
Mild B3 deficiency starts with vague symptoms: fatigue, weakness, poor appetite, and digestive complaints like indigestion or irregular bowel habits. These early signs often appear before anything more distinctive and can easily be mistaken for other conditions.
Severe deficiency causes pellagra, historically described by its “three Ds”: dermatitis, diarrhea, and dementia. Left untreated, a fourth D follows: death. The skin symptoms are the most recognizable. A sunburn-like rash appears symmetrically on sun-exposed skin, particularly the backs of the hands, forearms, feet, and a band across the lower neck and upper chest known as Casal’s necklace. The rash has a sharp line between affected and normal skin, and the affected areas eventually darken and peel.
Digestive symptoms include nausea, a sore mouth, a swollen bright-red tongue, and chronic diarrhea from inflammation spreading through the entire gastrointestinal tract. Neurological effects begin with anxiety, depression, irritability, and fatigue, then progress to confusion, tremors, and in about 4 to 10% of chronic cases, full dementia. Pellagra is now rare in industrialized countries but still occurs in populations dependent on unfortified corn-based diets, in chronic alcoholism, and in people taking certain medications that interfere with B3 metabolism.
Niacinamide in Skincare
Niacinamide has become one of the most popular active ingredients in skincare, and for good reason. Applied topically at concentrations of 2 to 5%, it helps strengthen the skin’s moisture barrier, reduce redness and inflammation, improve uneven skin tone, and regulate oil production. Most over-the-counter serums and moisturizers fall within this concentration range. Higher concentrations (around 4%) tend to be more effective for inflammatory skin conditions but can cause mild irritation in some people. Unlike many active skincare ingredients, niacinamide is generally well tolerated and pairs easily with other products in a routine.
Niacin and Cholesterol
For decades, high-dose niacin (not niacinamide) was prescribed to improve cholesterol levels. It raises HDL (“good”) cholesterol and lowers triglycerides more effectively than many alternatives. However, the most recent guidelines from the American Heart Association and American College of Cardiology no longer recommend niacin for routine use. Large clinical trials showed that adding niacin to standard cholesterol-lowering therapy did not reduce heart attacks or strokes, despite improving cholesterol numbers on paper. Combined with its poor tolerability, including the flush reaction and potential liver stress, niacin is now considered a last-line option reserved for severe cases of very high triglycerides when other treatments fail.
The Niacin Flush
If you’ve ever taken a niacin supplement and felt your face turn hot and red within 20 to 30 minutes, you’ve experienced the niacin flush. This happens because niacin triggers the release of prostaglandins, signaling molecules that cause blood vessels in the skin to widen rapidly. The result is warmth, redness, tingling, and sometimes itching, usually across the face, neck, and chest. It’s harmless but uncomfortable, and it’s the main reason many people stop taking niacin supplements. Extended-release formulations reduce the intensity of the flush but don’t always eliminate it. Niacinamide, the other form of B3, does not trigger this reaction at all.
Safety and Upper Limits
From food alone, there’s no risk of getting too much vitamin B3. The concerns apply to supplements and therapeutic doses. The tolerable upper intake level for adults is 35 mg per day from supplements and fortified foods. This limit was set based on the flushing reaction, which is the first noticeable side effect as doses climb. At the high doses once used for cholesterol management (1,000 to 3,000 mg per day), niacin can cause liver damage, worsen blood sugar control, trigger gout flares, and cause gastrointestinal distress. These risks are why high-dose niacin should only be used under medical supervision, and why the supplement aisle versions (typically 100 to 500 mg) still deserve respect rather than casual use.