Water Soluble Vitamins

Mnemonic

“B and C are water soluble; everything else is fat soluble”, and being water soluble means they are not stored and are excreted in urine, so deficiency develops quickly and toxicity is rare.

• B1 thiamine - beriberi, Wernicke-Korsakoff
• B2 riboflavin - angular stomatitis
• B3 niacin - pellagra: the three Ds, dermatitis, diarrhoea, dementia
• B5 pantothenate - burning feet
• B6 pyridoxine - sideroblastic anaemia, neuropathy, seizures. Depleted by isoniazid
• B7 biotin - dermatitis, alopecia
• B9 folate - megaloblastic anaemia, neural tube defects
• B12 cobalamin - megaloblastic anaemia plus subacute combined degeneration
• C ascorbate - scurvy

B12 is the exception to the storage rule: the liver holds 2 to 4 years’ worth, which is why dietary deficiency takes years to appear while folate deficiency takes months.

Excess B6 is the exception to the toxicity rule, causing a sensory neuropathy.

Expansion

The B group and vitamin C share:

• Absorption independent of fat
• Minimal storage, so deficiency develops relatively quickly
• Excretion in urine, so toxicity is uncommon
• Function almost entirely as coenzymes

Two important exceptions:

• B12 is stored in the liver for 3 to 5 years, so deficiency takes years to appear after absorption fails. Folate stores last only a few months
• B6 in high dose causes a sensory peripheral neuropathy, one of the few water soluble vitamin toxicities

Deficiency states worth pairing with the vitamin

• B1 thiamine: beriberi and Wernicke encephalopathy
• B2 riboflavin: angular stomatitis, glossitis
• B3 niacin: pellagra, the three Ds
• B6 pyridoxine: neuropathy, sideroblastic anaemia, seizures in neonates
• B9 folate: megaloblastic anaemia, neural tube defects
• B12: megaloblastic anaemia, subacute combined degeneration
• C: scurvy

Niacin is partly synthesised from tryptophan, which is why pellagra occurs in carcinoid syndrome (tryptophan diverted to serotonin), in Hartnup disease (impaired tryptophan absorption) and in isoniazid therapy.