Vitamin B7 (Biotin): Function and Deficiency to Vitamin B9 (Folate): Deficiency, Causes, and Prevention

Vitamin B7

Also called biotin.

Function

Cofactor for carboxylation enzymes (which add a 1-carbon group):

• Pyruvate carboxylase (gluconeogenesis): pyruvate (3C) → oxaloacetate (4C)
• Acetyl-CoA carboxylase (fatty acid synthesis): acetyl-CoA (2C) → malonyl-CoA (3C)
• Propionyl-CoA carboxylase (fatty acid oxidation and branched-chain amino acid breakdown): propionyl-CoA (3C) → methylmalonyl-CoA (4C)

Deficiency

Relatively rare. Dermatitis, enteritis, alopecia. Caused by long-term antibiotic use or excessive ingestion of raw egg whites. “Avidin in egg whites avidly binds biotin.”

Vitamin B9

Also called folate.

Function

Converted to tetrahydrofolic acid (THF), a coenzyme for 1-carbon transfer/methylation reactions.

Important for the synthesis of nitrogenous bases in DNA and RNA.

Sources & Absorption

Found in leafy green vegetables. Also produced by gut microbiota.

Folate absorbed in jejunum (think foliage in the “jejun”gle).

Small reserve pool stored primarily in the liver.

Deficiency Symptoms & Labs

Deficiency of Vitamin B9 leads to macrocytic, megaloblastic anemia, characterized by hypersegmented polymorphonuclear cells (PMNs). Other symptoms include glossitis. Importantly, unlike vitamin B₁₂ deficiency, folate deficiency typically presents with no neurologic symptoms.

Laboratory findings include elevated homocysteine levels, but normal methylmalonic acid levels. This deficiency is often seen in chronic alcohol overuse and is particularly relevant during pregnancy.

Causes & Prevention

Deficiency can be caused by several drugs (eg, phenytoin, trimethoprim, methotrexate).

Supplemental folic acid is recommended at least 1 month prior to conception and during pregnancy to decrease the risk of neural tube defects.

It is also advised to give vitamin B₆ for the 9 months of pregnancy, and 1 month prior to conception.

Topics Covered:

• Vitamin B7 (Biotin): Function and Deficiency
• Vitamin B9 (Folate): Function, Sources, and Absorption
• Vitamin B9 (Folate): Deficiency, Causes, and Prevention