Vitamin A: Uses, Effects, Side Effects, Dosage, Interactions, Risks

Vitamin A is a vital nutritional component. If this is not supplied to the body, deficiency symptoms (hypo-/avitaminosis) occur. Different forms of vitamin A can be distinguished:

  • Vitamin A1 (retinol)
  • Vitamin A2 (3-dehydroretinol)
  • And other derivatives

Vitamin A is absorbed in the human body in the duodenum (duodenum) and in the upper jejunum (empty intestine). It is stored in the liver and bound to protein (retinol-binding protein – RBF) transported in the blood. Vitamin A is fat-soluble and is inactivated mainly by oxygen, but also by UV light. It is mainly found in dairy products, egg yolk, liver and in many fruits and vegetables – there as provitamin (carotenoids). An important task of vitamin A is the maintenance of vision, especially twilight/night vision. But it also plays an important role in metabolism as well as in growth (regulation of bone growth) and sexual development. Vitamin A has another important role as a protective substance for the ectoderm (e.g. epithelial cell regeneration of mucous membranes).

The process

Material needed

  • Blood serum

Preparation of the patient

  • Not necessary

Disruptive factors

  • The blood sample must be stored in the dark

Standard values

Value in μg/l Value in μmol/l
Vitamin A deficiency < 100-200 < 0,35- 0,7
Normal range 100-1.000 0,35- 3,5
Vitamin A overdose > 1.000-2.000 3,5- 7

Indications

Interpretation

Interpretation of increased values

  • Vitamin A overdose during vitamin A therapy (e.g., because of acne (e.g., acne vulgaris), psoriasis); the following symptoms may occur:
    • Alopecia (hair loss)
    • Anorexia nervosa (anorexia)
    • Arthralgia (joint pain)
    • Cephalgia (headache)
    • Cheilitis (inflammation of the lips)
    • Dysosmia (olfactory disorders)
    • Nausea (nausea)/vomiting
    • Periosteal swelling – thickening of the periosteum.
    • Irritability
    • Visual disturbances
    • Xeroderma (dry skin) – dry, red, scaly skin.

Interpretation of lowered values

  • Alimentary (nutritional)
    • Unilateral nutrition (parenteral nutrition)
    • Chronic high alcohol consumption
  • Malabsorption (disorder of absorption)
  • Maldigestion (disorder of digestion).
  • Diseases that may be associated with decreased serum vitamin A levels.
    • Malformations associated with vitamin A deficiency during pregnancy.
    • Follicular hyperkeratosis (“toad skin“) – cornification disorder.
    • Premature
    • Glossitis (inflammation of the oral mucosa)
    • Bone formation disorders
    • Liver cirrhosis – connective tissue remodeling of the liver with functional impairment.
    • Nephrotic syndrome – complex of symptoms in various kidney diseases leading to increased permeability of membranes.
    • Nycteralopia (night blindness).
    • RBF deficiency (retinol-binding protein).
    • Growth disorders
    • Xeroderma – dry skin
    • Xerophthalmia – dry eyes
  • Increased need
    • Pregnant women / breastfeeding

Further notes

  • The normal requirement for vitamin A is 0.8 mg/d for women and 1.0 mg/d for men.

Attention. Note on the state of supply (National Consumption Study II 2008) 15% of men and 10% of women do not reach the recommended daily intake. Particularly affected are 14-18 year old men and women.