The most frequently occurring clinical indicator of vitamin A deficiency is night-blindness, which is the earliest manifestation of xerophthalmia.
In its mild form it is generally noticeable after stress from a bright light that bleaches the rhodopsin (visual purple) found in the retina. Vitamin A deficiency prolongs the time to regenerate rhodopsin, and thus delays adaptation time in dark environments.
Night-blind young children tend to stumble when going from bright to dimly-lit areas and they, as well as night-blind mothers, tend to remain inactive at dusk and at night.
Isaac Bashevis Singer
What do they know-all these scholars, all these philosophers, all the leaders of the world - about such as you? They have convinced themselves that man, the worst transgressor of all the species, is the crown of creation. All other creatures were created merely to provide him with food, pelts, to be tormented, exterminated.
Undernutrition is a form of malnutrition. (Malnutrition also includes overnutrition).
Undernutrition can result from:
- inadequate ingestion of nutrients,
- impaired metabolism,
- loss of nutrients due to diarrhea,
- increased nutritional requirements.
Undernutrition progresses in stages: it may develop slowly when it is due to anorexia or very rapidly. First, nutrient levels in blood and tissues change, followed by intracellular changes in biochemical functions and structure. Ultimately, symptoms and signs appear. Diagnosis is by history, physical examination, body composition analysis, and sometimes laboratory tests.
Undernutrition from micronutrient deficiencies, or "hidden hunger", affects over 2 billion people globally and can lead to reduced growth and cognitive development, birth defects, blindness, and overall poor health. Vitamin A deficiency, iron deficiency anaemia and iodine deficiency disorders are among the most common forms of micronutrient malnutrition.