Vitamin A: Function

Vitamin A includes retinal, retinol, and retinoic acid. It functions as an antioxidant and is a constituent of visual pigments, specifically retinal, which is essential for normal differentiation of epithelial cells into specialized tissue, such as pancreatic cells and mucus-secreting cells, thereby preventing squamous metaplasia.

Retinol is vitamin A, often associated with retin-A, used topically for wrinkles and acne. It’s found in liver and leafy vegetables. Supplementation in vitamin A-deficient measles patients can improve outcomes. Oral isotretinoin is used to treat severe cystic acne, and all-trans retinoic acid is used for acute promyelocytic leukemia.

Vitamin A: Deficiency

Deficiency in Vitamin A can lead to several conditions, including night blindness (nyctalopia), dry, scaly skin (xerosis cutis), and dry eyes (xerophthalmia). A common sign is conjunctival squamous metaplasia, which can manifest as Bitot spots—keratin debris with a foamy appearance on the conjunctiva. Severe deficiency can progress to corneal degeneration (keratomalacia) and also lead to immunosuppression.

Vitamin A: Excess and Toxicity

Excess Vitamin A can lead to both acute and chronic toxicity. Acute toxicity symptoms include nausea, vomiting, and increased intracranial pressure, which may manifest as vertigo and blurred vision. Chronic toxicity can cause alopecia, dry skin with scaliness, hepatic toxicity and enlargement, arthralgias, and idiopathic intracranial hypertension.

Importantly, Vitamin A derivatives like isotretinoin are teratogenic, meaning they can cause birth defects such as cleft palate and other cardiac abnormalities. Therefore, a negative pregnancy test and two forms of contraception are required before prescribing isotretinoin to women of childbearing potential.

Vitamin B1: Function (Thiamine)

Vitamin B1 is also known as thiamine. In its active form, thiamine pyrophosphate (TPP), it serves as a crucial cofactor for several dehydrogenase enzyme reactions. These include:

• Branched-chain ketoacid dehydrogenase
• α-Ketoglutarate dehydrogenase (involved in the TCA cycle)
• Pyruvate dehydrogenase (which links glycolysis to the TCA cycle)
• Transketolase (part of the HMP shunt)

Vitamin B1: Deficiency

Thiamine deficiency leads to impaired glucose breakdown, which in turn causes ATP depletion. This particularly affects highly aerobic tissues like the brain and heart first. In patients with chronic alcohol overuse or malnutrition, it’s crucial to administer thiamine before dextrose to reduce the risk of precipitating Wernicke encephalopathy. Diagnosis of thiamine deficiency can be made by observing an increase in red blood cell transketolase activity following Vitamin B1 administration.

Vitamin B1: Wernicke-Korsakoff Syndromes

Vitamin B1: Beriberi

To remember that beriberi is associated with Vitamin B1, think of the spelling ‘BeriBer1’.

Topics Covered:

• Vitamin A: Functions and Forms
• Vitamin A: Deficiency Symptoms
• Vitamin A: Toxicity and Teratogenicity
• Vitamin B1: Thiamine’s Role in Metabolism
• Vitamin B1: Deficiency and Diagnosis
• Vitamin B1: Wernicke-Korsakoff Syndromes
• Vitamin B1: Beriberi Forms