B vitamins are a group of eight nutrients that help your body convert food into energy, build red blood cells, and keep your brain and nervous system working properly. They’re water-soluble, meaning your body doesn’t store large reserves of most of them, so you need a steady supply from food or supplements. Each of the eight B vitamins has a distinct role, but they often work together.
The Eight B Vitamins and What They Do
B1 (thiamine) helps your cells convert carbohydrates into usable energy and supports nervous system function.
B2 (riboflavin) plays a role in body growth, red blood cell production, and releasing energy from food. It also helps keep your skin, eyes, and nervous system healthy.
B3 (niacin) maintains healthy skin and nerves. At higher doses, it can also lower triglycerides, a type of fat in the blood.
B5 (pantothenic acid) is essential for metabolizing food and contributes to hormone and cholesterol production.
B6 (pyridoxine) helps form hemoglobin, the protein in red blood cells that carries oxygen. It’s also critical for brain function because it’s directly involved in producing mood-regulating brain chemicals like serotonin, dopamine, and GABA.
B7 (biotin) is needed in small amounts to help your body metabolize proteins and carbohydrates and to produce fatty acids.
B9 (folate) helps form healthy red blood cells and is essential for DNA production, which controls tissue growth and cell function. During pregnancy, adequate folate reduces the risk of neural tube defects like spina bifida.
B12 (cobalamin) supports metabolism, red blood cell formation, and the central and peripheral nervous systems. It’s the only B vitamin found naturally in animal foods alone.
How B Vitamins Power Your Energy
When people say B vitamins “give you energy,” they don’t mean the vitamins act like caffeine. Instead, B vitamins function as coenzymes, meaning they assist the chemical reactions that break down carbohydrates, fats, and proteins into ATP, the molecule your cells actually use for fuel. Without enough of them, those reactions slow down, and fatigue is one of the earliest symptoms of deficiency.
This is why B vitamins are often bundled into a “B complex” supplement. They work in concert during energy production, so a shortfall in one can bottleneck the whole process.
Brain and Nerve Health
B12 is especially important for your nervous system because it helps build and maintain myelin, the fatty coating that wraps around nerve fibers and allows them to transmit signals efficiently. B12 contributes to making both the fatty acids and the proteins that form myelin, and it supports nerve fiber regrowth after damage. When B12 levels drop too low, myelin breaks down, leading to numbness, tingling, and balance problems.
B6 has a different but equally important neurological role. In your brain, it drives the production of serotonin (from the amino acid tryptophan) and dopamine, plus several other signaling chemicals including GABA, which helps regulate anxiety. Low B6 levels have been linked to mood disturbances for this reason.
Heart Health and Homocysteine
Three B vitamins, B6, B9, and B12, work together to break down homocysteine, an amino acid that can accumulate in your blood. When these vitamins process homocysteine, they convert it into methionine (an antioxidant that builds proteins) and cysteine (which reduces inflammation and supports immune function). Elevated homocysteine is associated with higher cardiovascular risk, and doctors sometimes recommend B vitamin supplements to bring levels down. That said, lowering homocysteine with supplements alone has not been shown to directly reduce the risk of heart disease.
Folate, Folic Acid, and Pregnancy
Folate is the general term for vitamin B9, which occurs naturally in foods like leafy greens. Folic acid is the synthetic, more stable form added to supplements and fortified foods. The distinction matters during pregnancy: folic acid is the only form of folate proven to help prevent neural tube defects. The CDC notes that no studies have shown other supplemental forms of folate, such as 5-MTHF, provide the same protection. Most prenatal vitamins contain 400 to 800 mcg of folic acid.
Biotin for Hair, Skin, and Nails
Biotin (B7) is heavily marketed for strengthening hair, skin, and nails, but the evidence behind those claims is thin. The NIH Office of Dietary Supplements reports that the research supporting biotin for brittle nails consists of just three small studies, none of which included a placebo group. Evidence for hair benefits comes only from case reports in children, and the skin data is limited to case reports in infants with existing deficiencies. If you’re not deficient in biotin, there’s little reason to expect a supplement will change the appearance of your hair or nails.
Signs of B Vitamin Deficiency
B12 deficiency is among the most common and most consequential. Early symptoms include fatigue, lightheadedness, pale skin, irritability, and loss of appetite. As the deficiency progresses, it can cause numbness and tingling in the hands and feet, loss of balance, difficulty concentrating, and a swollen or red tongue. In severe, prolonged cases, B12 deficiency can lead to confusion, personality changes, and even hallucinations. The condition it causes, a type of anemia where red blood cells grow abnormally large and can’t function properly, is called megaloblastic anemia.
Deficiencies in other B vitamins produce overlapping symptoms. Low B6 can cause skin rashes, cracked lips, and mood changes. Low folate also leads to anemia and fatigue. Low thiamine affects the nervous system and, in extreme cases, can cause serious brain damage.
Best Food Sources
Most people eating a varied diet get enough B vitamins from food. Whole grains, eggs, dairy, meat, legumes, seeds, and dark leafy greens collectively cover the full spectrum. B12 is the notable exception because it exists naturally only in animal products. The richest sources, per 3-ounce serving: clams (84 mcg), trout (5.4 mcg), salmon (4.9 mcg), canned tuna (2.5 mcg), and beef (1.5 mcg). A single large egg provides about 0.6 mcg.
If you follow a vegan or vegetarian diet, B12 requires deliberate planning. Fortified breakfast cereals can deliver around 6 mcg per serving, and fortified soy milk provides about 1.7 mcg per cup. Many plant-based eaters rely on a B12 supplement to close the gap, since the consequences of long-term deficiency are serious and the early symptoms are easy to dismiss as general tiredness.
Who Is Most at Risk for Low Levels
Beyond vegans and vegetarians, older adults are at higher risk for B12 deficiency because the stomach produces less of the acid needed to absorb it from food as you age. People with digestive conditions that affect absorption, heavy alcohol use, or certain medications that interfere with B vitamin metabolism are also more vulnerable. Pregnant and breastfeeding women have higher folate and B12 needs, making supplementation especially important during those periods.