Which of the following is a micro-mineral found in human body fluids / tissues ?

Correct — option (3), Iodine.

Dietary minerals are grouped by how much the body needs. Macrominerals are needed in larger amounts; micro-minerals, also called trace minerals, only in small amounts.

MedlinePlus, the US National Library of Medicine's health site, names iron, manganese, copper, iodine, zinc, cobalt, fluoride and selenium among the trace minerals. It names calcium, phosphorus, magnesium, sodium, potassium, chloride and sulphur among the macrominerals.

Iodine's small requirement shows the difference. India's National Health Mission states that it is required at 100–150 micrograms daily for normal growth and development.

The body uses iodine to make the thyroid hormones. Phosphorus, sulphur and magnesium, the other three options, are all macrominerals.

The idea to remember: iodine, iron, zinc, copper and selenium are micro-minerals; calcium, phosphorus, magnesium and sulphur are macrominerals.

Why the others are wrong

• (1)
  Phosphorus — Phosphorus is a macromineral. Most of the body's phosphorus lies in bones and teeth, where it combines with calcium as calcium phosphate, making it the mineral that partners calcium in bones and teeth.

  It is also part of ATP, DNA and the phospholipids of cell membranes. It is needed in far larger amounts than iodine.

• (2)
  Sulphur — Sulphur is counted among the macrominerals. The body gets most of it through the sulphur-containing amino acids methionine and cysteine.

  Cysteine's sulphur forms the bonds that give strength to proteins such as keratin in hair and nails. Sulphur is not a trace mineral.

• (4)
  Magnesium — Magnesium is a macromineral. It acts as a cofactor for hundreds of enzymes, including those that use ATP, and a large share of the body's magnesium is stored in bone.

  In plants it is the central atom of the chlorophyll molecule. None of this makes it a trace mineral in human nutrition.

Minerals are inorganic elements the body cannot make, so they must come from food and water. They build bones and teeth, carry oxygen, balance fluids, and form parts of enzymes and hormones.

Nutrition science splits them by the amount required. Macrominerals are needed in larger amounts, commonly defined as 100 mg or more a day. Micro-minerals, or trace minerals, are needed in much smaller amounts, some only in micrograms.

"Trace" describes the quantity needed, not the importance. A shortage of iodine or iron causes serious disease.

Key facts

• MedlinePlus names calcium, phosphorus, magnesium, sodium, potassium, chloride and sulphur among the macrominerals.
• MedlinePlus names iron, manganese, copper, iodine, zinc, cobalt, fluoride and selenium among the trace minerals.
• India's National Health Mission states that iodine is required at 100–150 micrograms daily for normal human growth and development.
• The thyroid hormones thyroxine (T4) and triiodothyronine (T3) carry four and three iodine atoms respectively.
• In August 1992 the National Goitre Control Programme was renamed the National Iodine Deficiency Disorders Control Programme (NIDDCP).

Common traps

• "Trace" refers to the amount needed, not importance. Iodine is needed in micrograms a day, yet its deficiency causes goitre and cretinism.
• Magnesium is needed in smaller amounts than calcium, but its requirement is still in hundreds of milligrams a day, which keeps it among the macrominerals.
• Iodine, fluorine and chlorine sit in the same periodic-table group, yet chloride is a macromineral while iodine and fluoride are trace minerals. Chemical family does not decide the nutritional class.

UnlockIAS will link similar questions from RAS Pre 2023 here once that paper is published on this site.

• practice — not a real PYQ

  Which of the following is a macromineral in human nutrition?

  • (a)Zinc
  • (b)Selenium
  • (c)Calcium
  • (d)Copper
  Answer(3) — Calcium is needed in large amounts, mainly for bones and teeth, and is a macromineral. Options (1), (2) and (4), zinc, selenium and copper, are all trace minerals.
• practice — not a real PYQ

  Goitre, an enlargement of the thyroid gland, is mainly associated with deficiency of which micro-mineral?

  • (a)Iron
  • (b)Iodine
  • (c)Zinc
  • (d)Fluoride
  Answer(2) — The thyroid needs iodine to make its hormones, and iodine deficiency leads to goitre. Option (1), iron, is linked to anaemia; option (3), zinc, to impaired growth and immunity; option (4), fluoride, to dental health.