Overview

Vitamins are essential molecules required in small amounts for adequate functioning of metabolism. They are used for the prevention or treatment of their deficiencies but are not advised for use as dietary supplements. Their overuse can be harmful, and evidence regarding their use as ‘health boosters’ is lacking.

Vitamins are classified as:

  • Fat-soluble – may accumulate in the body, such as in the liver:
    • Vitamin A
    • Vitamin D
    • Vitamin E
    • Vitamin K
  • Water-soluble – more readily excreted from the body, therefore toxicity is generally less likely:
    • Vitamins B1, B3, and B6
    • Vitamin C

Vitamin A

Overview

Also known as retinol, vitamin A is a fat-soluble vitamin and has the following functions:

  • Formation of retinal, which is essential for retinal cell responses to light
  • Acts as an antioxidant

Deficiency

Vitamin A deficiency can lead to:

  • Xerophthalmia – describes a spectrum of pathologies affecting the conjunctiva, cornea, and retina, including night blindness and corneal scarring

Overdose

Features of overdose may include:

  • Rough skin
  • Dry hair
  • Hepatomegaly
  • Increased erythrocyte sedimentation rate
  • Hypercalcaemia
  • Increased serum ALP

Cautions

Cautions include:

  • High doses of vitamin A may be teratogenic:
    • This is because retinol converts to retinoic acid, which can lead to congenital defects if levels are too high or low
    • Foods with liver have high vitamin A levels and should be avoided during pregnancy

Vitamin B1 (Thiamine)

Overview

Also known as thiamine, vitamin B1 is a water-soluble vitamin whose phosphate derivatives are essential in the catabolism of sugars and amino acids.

Thiamine deficiency can occur due to:

  • Alcohol excess:
    • Due to alcohol inhibiting the uptake of thiamine
  • Malnutrition

Deficiency

Thiamine deficiency can lead to:

Vitamin B3 (Niacin)

Overview

Also known as niacin, vitamin B3 is a precursor for the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are crucial in cell metabolism.

Deficiency

A deficiency of B3 can lead to pellagra which is characterised by:

Vitamin B6 (Pyridoxine)

Overview

Also known as pyridoxine, vitamin B6 is involved in amino acid, lipid, and glucose metabolism, and the formation of neurotransmitters. 

Deficiency

Deficiency typically leads to peripheral neuropathy and may occur secondary to:

Overdose

  • Excessive pyridoxine over long periods can cause painful and irreversible neuropathy.

Vitamin C (Ascorbic Acid)

Overview

Also known as ascorbic acid, vitamin C is involved in many biological functions such as wound healing and collagen synthesis. It is found in many fruits and vegetables such as oranges, tomatoes, potatoes, broccoli, and spinach. Its deficiency is associated with malnutrition and poverty.

Deficiency

Reduced vitamin C can lead to scurvy, which occurs secondary to impaired wound healing and collagen synthesis. Features include:

  • Easy bruising and ecchymosis
  • Poor wound healing
  • Gingivitis bleeding gums
  • Weakness
  • Malaise
  • Anorexia
  • Depression
  • Synovitis

Cautions

Scurvy is exceedingly rare in the UK. Patients with these features may have an underlying haematological malignancy, therefore, investigations should not be delayed by a trial of vitamin C treatment. 

Vitamin D

Overview

Vitamin D describes compounds that can prevent or cure rickets, including vitamin D2 (calciferol), vitamin D3 (cholecalciferol), dihydrotachysterol, alfacalcidol (1α-hydroxycholecalciferol), and calcitriol (1,25-dihydroxycholecalciferol).

Deficiency

Deficiency may occur in:

  • People whose exposure to sunlight is limited (e.g. those that are housebound, confined indoors, or cover their skin)
  • People with dark skin as their skin is less efficient at synthesising vitamin D
  • Pregnant and breastfeeding women
  • Children under 4 years of age
  • Intestinal malabsorption
  • Chronic liver disease

Vitamin D requires activation via hydroxylation in the kidneys to its active form, therefore hydroxylated derivatives (such as alfacalcidol or calcitriol) may need to be given to those with chronic kidney disease.

A deficiency of vitamin D can lead to rickets or osteomalacia.

Overdose

Vitamin D overdose can lead to hypercalcaemia.

Vitamin E (Tocopherol)

Overview

Also known as tocopherol, vitamin E is a fat-soluble antioxidant. Its deficiency is rare as this usually occurs secondary to problems with digesting fat, rather than a dietary deficiency. There is little evidence that oral supplementation is essential in adults, even if there is fat malabsorption secondary to cholestasis.

Vitamin K

Overview

Vitamin K is found in leafy green vegetables and some oils, such as olive oil. It is essential in the synthesis of clotting factors II VII, IX, and X, and is necessary for the normal calcification of bone.

Deficiency

Since vitamin K is fat-soluble, patients with fat malabsorption (such as biliary obstruction or hepatic disease) are at an increased risk of deficiency.

Coumarin anticoagulants (such as warfarin) exert their effects by interfering with vitamin K metabolism).

Vitamin K deficiency can lead to:

  • Excessive bleeding
  • Haemorrhagic disease of the newborn

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