What are the recommended dietary allowances (RDA) for each B‑vitamin (thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, biotin, folate, cobalamin) in healthy adults aged 19 years and older?

RDA of Vitamin B Complex for Adults

For healthy adults aged 19 years and older, the recommended dietary allowances for B vitamins are: Thiamin (Vitamin B1) 1.1–1.2 mg/day, Riboflavin (Vitamin B2) 1.3–1.6 mg/day, Niacin (Vitamin B3) not specified in provided evidence, Pantothenic Acid (Vitamin B5) not specified, Pyridoxine (Vitamin B6) 1.3–1.6 mg/day, Biotin (Vitamin B7) not specified, Folate (Vitamin B9) 330–400 µg DFE/day, and Cobalamin (Vitamin B12) 2.4 µg/day. 1

Specific B Vitamin RDAs

Thiamin (Vitamin B1)

• UK guidelines recommend 0.9 mg/day for men and 0.8 mg/day for women aged ≥50 years, though these values are 10–25% lower than recommendations from Germany, Switzerland, Australia, New Zealand, and the USA. 2
• The general adult RDA is approximately 1.1–1.2 mg/day based on minimum requirements per 1000 kcal energy intake. 2

Riboflavin (Vitamin B2)

• The RDA is 1.6 mg/day for adults, with current intakes in Irish males averaging 2.0 mg/day and females 3.7 mg/day. 2
• Biochemical deficiency (erythrocyte glutathione reductase activation coefficient indicating deficiency) occurs in approximately 5.3% of the general population despite adequate reported intake. 3

Pyridoxine (Vitamin B6)

• The RDA is 1.3 mg/day for adults under 50 years and 1.6 mg/day for older adults. 1
• Current intakes in Irish populations show males consuming 3.1 mg/day and females 5.4 mg/day, well above the RDA. 2

Folate (Vitamin B9)

• The RDA is 330–400 µg dietary folate equivalents (DFE) per day for adults. 2, 1
• Women of childbearing age should consume 400–800 µg daily to prevent neural tube defects, even if not actively planning pregnancy. 1
• Current intakes in Irish males average 356 µg DFE/day and females 269 µg DFE/day, indicating many women fall short of optimal intake. 2

Cobalamin (Vitamin B12)

• The standard RDA is 2.4 µg/day for healthy adults based on hematological status. 1, 4, 5
• However, emerging evidence suggests 4–7 µg/day may be optimal for maintaining steady biomarker concentrations (serum B12, holotranscobalamin, methylmalonic acid, and homocysteine). 5
• The European Food Safety Authority (EFSA) recommends 4 µg/day based on biomarker combinations, which is higher than the US/UK standard. 2

Important Clinical Considerations

Age-Related Absorption Issues

• 10–30% of adults aged 51+ have protein-bound vitamin B12 malabsorption due to reduced gastric acid and pepsin secretion, making synthetic B12 (from fortified foods or supplements) preferable to food-bound B12. 4
• Atrophic gastritis affects up to 20% of older adults, causing food-bound B12 malabsorption while crystalline B12 absorption remains intact. 6

Dietary Sources vs. Supplementation

• Natural food sources should be prioritized: meat provides B12 and B6; milk and dairy provide riboflavin and B6; green leafy vegetables, legumes, and liver provide folate. 2
• Fortified breakfast cereals are key contributors to B vitamin intakes, particularly important for older adults and those with restricted diets. 2
• Most healthy adults can obtain adequate B vitamins through diet alone without supplementation if consuming a balanced diet with adequate animal products, whole grains, and vegetables. 1

High-Risk Populations Requiring Higher Intakes

• Adults over 65 years may benefit from a daily multivitamin, especially with reduced energy intake, as age-related declines in B vitamin status occur even in apparently healthy elderly. 2, 1
• Strict vegetarians must supplement with B12 (500–1000 µg/day orally) and consider additional iron, zinc, and calcium supplementation. 1
• Individuals on calorie-restricted diets (<1500 kcal/day) should take a multivitamin to ensure adequate micronutrient intake. 1

Common Pitfalls

• Biochemical deficiency can occur despite adequate reported intake, as demonstrated by studies showing 6.4% thiamin deficiency and 5.3% riboflavin deficiency in populations with intake above two-thirds of the RDA. 3
• Cooking methods, storage, and co-ingestion of substances like alcohol, sulfites, tannins, and certain medications (diuretics, PPIs, metformin) reduce B vitamin bioavailability, making dietary assessment alone insufficient for determining true status. 2
• Subclinical deficiencies remain poorly understood, and current RDA values may not reflect optimal levels for preventing age-related conditions like sarcopenia. 2

Practical Supplementation Approach

• If choosing a multivitamin, select one providing approximately 100% of the RDA for most nutrients, not megadoses. 1
• For B12 specifically, 500–1000 µg/day orally is safe and commonly used, as excess is readily excreted without toxicity. 6
• Fortified foods can effectively meet B vitamin needs, particularly for B12 in older adults with malabsorption, as synthetic B12 is well absorbed even when intrinsic factor-mediated absorption is impaired. 4