B Vitamins Benefits: All 8 B Vitamins, Functions & Deficiency Symptoms【2026】

“Taking B vitamins makes me less tired” is something many people say from personal experience — but B complex vitamins do far more than fight fatigue. All 8 members of the B vitamin family each have distinct roles in supporting energy metabolism, nervous system function, DNA synthesis, red blood cell production, and more. A deficiency in any one of them can trigger specific health problems.

Shared Characteristics of B Vitamins

Water-soluble: B vitamins are water-soluble, and any excess is excreted through urine rather than accumulating in the body the way fat-soluble vitamins (A, D, E, K) do. This means:

• They must be replenished daily — there is no reserve to draw upon
• Excess amounts are generally safer than with fat-soluble vitamins (though high-dose B6 and B3 still warrant caution)
• Stress, alcohol consumption, and certain medications accelerate B vitamin depletion

Coenzyme role: Most B vitamins function as coenzymes — essential cofactors for enzyme-driven reactions throughout the body, particularly the tricarboxylic acid (TCA) cycle that powers cellular energy production.

All 8 B Vitamins: Functions and Deficiency Symptoms

B1 — Thiamine

Primary Functions:

• Essential coenzyme for converting carbohydrates into energy
• Maintains normal nerve signal transmission
• Supports cardiac muscle function

Deficiency Symptoms:

• Mild deficiency: fatigue, poor appetite, irritability
• Severe deficiency: Beriberi — peripheral neuropathy and cardiac dysfunction
• Wernicke’s encephalopathy: the most serious deficiency syndrome, classically associated with chronic heavy alcohol use

High-Risk Groups: Chronic heavy drinkers, patients on kidney dialysis, strict vegans

Daily Reference Intake (Taiwan DRI): Men 1.2 mg, Women 0.9 mg

B2 — Riboflavin

Primary Functions:

• Participates in cellular oxidation-reduction reactions (FAD/FMN coenzymes)
• Maintains health of skin, eyes, and the nervous system
• Activates other B vitamins (B6, B9, B12) so they can function

Deficiency Symptoms:

• Cracking at the corners of the mouth (angular stomatitis)
• Redness and soreness of the tongue (glossitis)
• Sensitivity to light, redness of the eyes

Natural Sources: Milk, cheese, eggs, liver, almonds

Daily Reference Intake: Men 1.3 mg, Women 1.0 mg

B3 — Niacin

Primary Functions:

• The most critical coenzyme in energy metabolism (NAD+/NADH)
• At pharmacological doses, can lower triglycerides and raise HDL (good cholesterol)
• Supports DNA repair mechanisms
• Maintains skin and nervous system health

Deficiency Symptoms:

• Pellagra: the classic triad of dermatitis, diarrhea, and dementia (the “3 Ds”)

Important Notes:

• Standard supplement doses (20–50 mg): safe for general use
• High doses (500 mg+): may cause “niacin flush” — a harmless skin flushing sensation from blood vessel dilation, not an allergic reaction
• Very high doses (1,000 mg+) long-term require medical supervision; potential liver effects

Daily Reference Intake: Men 16 mg NE, Women 14 mg NE (Niacin Equivalents)

B5 — Pantothenic Acid

Primary Functions:

• Essential component of Coenzyme A (CoA), which participates in fatty acid synthesis and oxidation
• Supports synthesis of adrenal hormones and cholesterol
• Contributes to wound healing and skin barrier function

Deficiency Symptoms: B5 is broadly distributed across foods, making severe deficiency rare. Mild deficiency may present as fatigue or a burning sensation in the feet (Burning Feet Syndrome).

Daily Reference Intake: 5 mg (Adequate Intake value)

B6 — Pyridoxine

Primary Functions:

• Coenzyme for over 100 enzymes, primarily involved in amino acid metabolism
• Neurotransmitter synthesis (serotonin, dopamine, GABA)
• Immune function regulation
• Reduces homocysteine levels, offering cardiovascular protection

Deficiency Symptoms:

• Peripheral neuritis (tingling or numbness in hands and feet)
• Depression and anxiety
• Angular stomatitis and glossitis
• Severe deficiency in pregnant women may affect fetal neural development

High-Risk Groups: Older adults (declining absorption), users of certain antibiotics or antihypertensives, kidney disease patients

Safety Note: Long-term intake exceeding 200 mg per day may cause sensory neuropathy.

Daily Reference Intake: Adults 1.5–1.6 mg; 50+ adults 1.7–1.9 mg

B7 — Biotin

Primary Functions:

• Coenzyme for fat, glucose, and amino acid metabolism
• Maintains hair, nail, and skin health (the origin of biotin’s “beauty vitamin” reputation)
• Normal gene regulation during embryonic development

Deficiency Symptoms:

• Brittle hair and hair loss
• Easily breaking nails
• Skin rash
• Eating raw egg whites over extended periods is a rare cause of deficiency (avidin binds biotin, blocking absorption)

Important Note: High-dose biotin supplementation (5,000 mcg or more) can interfere with many blood test results — including thyroid hormones and cardiac troponin — potentially producing false readings. Stop biotin 2–3 days before blood tests.

Daily Reference Intake: 30 mcg (Adequate Intake value)

B9 — Folate / Folic Acid

Primary Functions:

• Core coenzyme for DNA synthesis and repair
• Red blood cell production
• Neural tube development during pregnancy (one of the most critical prenatal nutrients)
• Lowers homocysteine, providing cardiovascular protection

Deficiency Symptoms:

• Megaloblastic anemia
• In pregnancy: dramatically increased risk of neural tube defects in the fetus (spina bifida, anencephaly)
• Fatigue and weakness

Natural Food Folate vs. Folic Acid Supplements: Natural food folate has approximately 50% bioavailability. Synthetic folic acid in supplements has bioavailability near 100%. However, individuals with MTHFR gene variants have difficulty converting synthetic folic acid into its active form, making 5-MTHF (methylfolate) a better choice for those individuals.

Pregnancy Recommendation: Begin supplementation 3 months before conception at 400–600 mcg per day; continue throughout pregnancy.

Daily Reference Intake: 400 mcg DFE (Dietary Folate Equivalents); pregnant women 600 mcg

B12 — Cobalamin

Primary Functions:

• Myelin synthesis and maintenance (the most irreplaceable B vitamin)
• DNA synthesis (works together with folate)
• Red blood cell production
• Homocysteine metabolism

Deficiency Symptoms (develop slowly, may remain latent for years):

• Megaloblastic anemia
• Peripheral neuropathy (numbness in the hands and feet, balance problems)
• Cognitive decline and increased dementia risk
• Neurological damage from severe deficiency may be irreversible

Highest-Risk Groups:

• Strict vegans (B12 is found almost exclusively in animal-derived foods)
• Adults 65 and older (gastric atrophy reduces intrinsic factor secretion)
• Long-term Metformin users (the diabetes drug interferes with B12 absorption)
• Long-term proton pump inhibitor (PPI) or H2 blocker users (reduced gastric acid impairs B12 absorption)

Supplement Forms:

Supplementation Note: Even though oral absorption efficiency is low for large doses, passive diffusion allows roughly 1% of a 1,000 mcg dose to still be absorbed — enough to correct deficiency in many cases. Severe deficiency may warrant injectable B12 (requires a prescription).

Daily Reference Intake: Adults 2.4 mcg; pregnant women 2.6 mcg; breastfeeding 2.8 mcg

The Synergy of B Vitamins

B vitamins do not operate independently — they form an interdependent metabolic network:

• B6 + B9 + B12: Work together to reduce homocysteine levels (cardiovascular protection)
• B2: Must activate B6 and B9 before they can function in their roles
• B12 + B9: Both depend on each other for DNA synthesis — deficiency in one impairs the function of the other

This is why supplement products designed as B complex combinations are generally more effective than single-B-vitamin supplements: the synergistic effects of the group far exceed what any member achieves alone.

Who Most Needs to Actively Supplement B Vitamins?

Further Reading

📖 Further Reading：How to Choose B Complex: Active vs Standard Forms, Dosage Guide