The disease goitre, which involves enlargement of the thyroid gland, commonly occurs in people whose regular diet does not contain a sufficient amount of which essential mineral?

Introduction / Context:
Goitre is a visible swelling in the front of the neck caused by enlargement of the thyroid gland. It is a common endocrine disorder in regions where certain nutrients are deficient in the local diet. Understanding the nutritional cause of goitre is important both for personal health and for public health measures such as iodised salt programmes. This question checks whether you can correctly identify the key dietary mineral whose deficiency is classically associated with goitre.

Given Data / Assumptions:

The disease mentioned is goitre, involving the thyroid gland. The cause is linked to insufficient intake of a specific mineral in the diet. Options list calcium, sodium, iodine, iron and zinc. We assume standard medical and nutritional knowledge about thyroid health.

Concept / Approach:
The thyroid gland requires iodine to synthesise thyroid hormones, mainly thyroxine (T4) and triiodothyronine (T3). When dietary iodine intake is low for a long time, the thyroid cannot make adequate hormone. In response, the pituitary gland secretes more thyroid stimulating hormone, which causes the thyroid to grow larger in an attempt to capture more iodine. This enlargement leads to goitre. Therefore, iodine deficiency is the classical nutritional cause of endemic goitre, especially in inland or mountainous regions where natural iodine content of soil and water is low.

Step-by-Step Solution:
Step 1: Recall that the thyroid gland uses iodine as an essential raw material to produce thyroid hormones. Step 2: Understand that low dietary iodine over time results in reduced hormone production and stimulates thyroid enlargement. Step 3: Look at the options and identify iodine as the only mineral directly linked to thyroid hormone synthesis. Step 4: Note that calcium is mainly involved in bones and nerve function, sodium in fluid balance and nerve impulses, iron in haemoglobin, and zinc in various enzymes and immune functions. Step 5: Conclude that goitre due to diet is primarily associated with a deficiency of iodine, making option c correct.

Verification / Alternative check:
Another way to verify is to think about common preventive measures recommended by health authorities. One widely promoted step is the use of iodised salt to prevent goitre and other iodine deficiency disorders. Public health campaigns often emphasise that iodised salt protects the thyroid gland. This specific focus on iodine, and not on calcium, sodium, iron or zinc, confirms that iodine deficiency is the correct nutritional cause linked with goitre in the exam context.

Why Other Options Are Wrong:
Calcium deficiency leads mainly to problems with bones and teeth, such as rickets in children or osteoporosis in adults, not typically to goitre. Sodium deficiency can disturb fluid balance and nerve function, but it does not cause thyroid enlargement. Iron deficiency results in anaemia due to reduced haemoglobin, showing as fatigue and pallor rather than neck swelling. Zinc deficiency may lead to poor wound healing and impaired immunity. None of these deficiencies classically cause goitre, so they are incorrect choices in this question.

Common Pitfalls:
Students sometimes confuse iron deficiency disorders, such as anaemia, with thyroid problems, especially if they memorise a long list of nutrient deficiencies without linking them firmly to specific diseases. Another pitfall is to overthink sodium because of its presence in common salt, but the goitre prevention aspect of table salt is due to added iodine, not its sodium content. To avoid these mistakes, remember a simple key: thyroid gland equals iodine, and goitre in nutritional context equals iodine deficiency. This direct association will help you answer similar questions quickly.

Final Answer:
Goitre commonly occurs in people whose diet lacks enough iodine, the essential mineral required for thyroid hormone production.