Which disease or condition in humans is classically caused by a dietary deficiency of iron and leads to reduced haemoglobin levels in the blood?

Introduction / Context:
Micronutrient deficiencies are a major public health concern, and iron deficiency is one of the most widespread nutritional problems worldwide. This question tests whether you can correctly link iron deficiency with the disease condition anaemia, which involves reduced haemoglobin levels and impaired oxygen carrying capacity of the blood. Distinguishing this from other deficiency disorders helps strengthen your knowledge of human nutrition.

Given Data / Assumptions:
- Iron is an essential component of haemoglobin in red blood cells.- Lack of iron in the diet or poor absorption decreases haemoglobin synthesis.- Several deficiency related diseases are listed in the options: beriberi, tetany, kwashiorkor, anaemia and rickets.- The question asks which condition is caused by deficiency of iron.

Concept / Approach:
Anaemia is a condition characterised by a decreased number of red blood cells or reduced haemoglobin concentration. Iron deficiency anaemia specifically arises when there is insufficient iron to produce haemoglobin. Symptoms include fatigue, pallor, shortness of breath and reduced work capacity. Other conditions mentioned are linked to different nutrients: beriberi to vitamin B1 deficiency, tetany to calcium or parathyroid hormone problems, kwashiorkor to lack of dietary protein and rickets to vitamin D deficiency affecting bones. Thus, the only disease in the list directly associated with iron deficiency is anaemia.

Step-by-Step Solution:
Step 1: Recall that haemoglobin, the oxygen carrying pigment in red blood cells, contains iron as a central component.Step 2: Understand that when the body does not receive enough iron, haemoglobin production falls, leading to iron deficiency anaemia.Step 3: Examine each disease in the options and recall its primary nutritional cause.Step 4: Recognise that only anaemia in option D is directly caused by iron deficiency, while the others relate to vitamins or protein.Step 5: Select option D as the correct answer.

Verification / Alternative check:
Public health programmes aimed at preventing iron deficiency focus on iron supplementation and iron rich foods to reduce anaemia rates, especially in women and children.Medical tests for suspected iron deficiency measure haemoglobin levels and iron status, confirming the close link between iron and anaemia.Standard textbooks clearly pair iron deficiency with anaemia rather than with beriberi, tetany, kwashiorkor or rickets, verifying the answer.

Why Other Options Are Wrong:
Option A is wrong because beriberi results from deficiency of vitamin B1 thiamine and affects the nervous and cardiovascular systems.Option B is wrong because tetany is associated with low blood calcium levels and parathyroid hormone imbalance, not iron deficiency.Option C is wrong because kwashiorkor is a protein energy malnutrition in children, characterised by oedema and muscle wasting.Option E is wrong because rickets arises from vitamin D deficiency leading to soft, deformed bones in growing children, not from lack of iron.

Common Pitfalls:
Students sometimes confuse different deficiency diseases because many of them cause weakness and growth problems, making symptom based recall difficult.Another pitfall is to memorise disease names without linking them to the underlying nutrient, leading to guesswork in exam questions.A simple memory aid is to remember the pair iron and anaemia together, just as thiamine pairs with beriberi and vitamin D pairs with rickets.

Final Answer:
The disease caused by deficiency of iron in humans is anaemia, which results from reduced haemoglobin levels in the blood.