SSC
Night blindness and xerophthalmia are caused by the deficiency of:
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Answer: Option B — Vitamin A
Detailed Solution
Vitamin A (retinol) is a fat-soluble vitamin that is essential for good vision, especially in dim light, for a healthy immune system, for normal growth, and for healthy skin and the linings of the eyes, respiratory tract and intestines.
In the retina of the eye, vitamin A is needed to form rhodopsin (visual purple), a light-sensitive pigment in the rod cells. Rod cells help us see in dim light. When there is not enough vitamin A, less rhodopsin is formed, and the person has difficulty seeing in dim light or at night. This is called night blindness (nyctalopia), usually the earliest sign of vitamin A deficiency.
If the deficiency continues, it causes xerophthalmia, meaning "dry eye". The conjunctiva and cornea become dry and thickened. Foamy grey spots called Bitot's spots may appear on the white of the eye. In severe cases, the cornea softens and ulcerates (keratomalacia), which can cause permanent blindness. Vitamin A deficiency is a leading cause of preventable blindness in children in developing countries. It also weakens immunity, increasing the risk of death from infections such as measles and diarrhoea.
Sources of vitamin A:
Animal sources (preformed vitamin A): liver, fish liver oils, egg yolk, milk, butter and ghee.
Plant sources (provitamin A carotenoids such as beta-carotene, which the body converts into vitamin A): carrots, sweet potatoes, pumpkins, spinach and other green leafy vegetables, mangoes and papayas. The orange colour of carrots comes from beta-carotene.
In India, children aged 9 months to 5 years are given vitamin A solution doses every six months under the national programme to prevent deficiency. "Golden rice" is a genetically modified rice developed to contain beta-carotene.
Since vitamin A is fat-soluble and stored in the liver, very high doses can be toxic.
Why not the other options?
- ✗Vitamin B12 deficiency causes pernicious anaemia.
- ✗Vitamin C deficiency causes scurvy (bleeding gums).
- ✗Vitamin D deficiency causes rickets.
Quick tip
Remember: Vitamin A = vision (rhodopsin); deficiency = night blindness, xerophthalmia, Bitot's spots; sources = carrots (beta-carotene), liver, mangoes; C = scurvy; D = rickets.
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Nutrition, Vitamins & Digestion — Preparation
This question tests your understanding of Nutrition, Vitamins & Digestion, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers human nutrition: carbohydrates, proteins, fats, vitamins and minerals, their sources and the diseases caused by their deficiency, balanced diet, and the human digestive system with its organs, glands and enzymes. Exam questions frequently ask which deficiency causes which disease (scurvy from lack of vitamin C, rickets from vitamin D, night blindness from vitamin A and beriberi from vitamin B1), the chemical names of vitamins, and where each nutrient is digested. The liver is the largest gland in the human body and produces bile. Practise the nutrition, vitamins and digestion questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.