Vitamin B complex basics: cofactors in energy metabolism and deficiency conditions

The vitamin B complex refers collectively to B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), and B12 (cobalamin). All function as cofactors in mitochondrial ATP production, the TCA (citric acid) cycle, fatty acid β-oxidation, and amino acid metabolism. A review (Kennedy, 2016) details each vitamin's role in these pathways, demonstrating their function as essential behind-the-scenes drivers of energy production.

8 vitamins

Number of vitamins in the B complex

B vitamin deficiencies produce characteristic symptoms. B1 deficiency causes beriberi and Wernicke encephalopathy; B3 deficiency causes pellagra (dermatitis, diarrhea, dementia); B12 and B9 deficiency causes megaloblastic anemia and neuropathy; long-term high-dose B6 is associated with peripheral neuropathy. Research demonstrates that supplementation in deficient individuals clearly improves these conditions. Vegans, older adults, and heavy alcohol users are at elevated risk for B12 deficiency and should be monitored.

High B12 deficiency risk

Vegans, older adults, heavy drinkers

All B vitamins are water-soluble, meaning excess is excreted in urine, which confers lower risk of accumulation toxicity compared with fat-soluble vitamins (A, D, E, K). However, high-dose B6 (over 50 mg/day) taken long-term has been associated with peripheral neuropathy (sensory disturbances, numbness), so staying within upper limits is important. For already-replete healthy individuals, supplementation may serve as an 'insurance policy', but scientific evidence for meaningful performance enhancement is limited.

>50 mg/day warrants caution

B6 dose level associated with peripheral neuropathy risk