Iodine: ICMR-NIN Requirement, Iodised Salt, FSSAI's Standard and India's Deficiency Programme

Iodine is a trace mineral with one known job: the thyroid gland builds it into the hormones that set the pace of metabolism and guide the growth of a baby's brain. ICMR-NIN's Nutrient Requirements for Indians sets the allowance at 140 mcg a day for adult men and women, a little over a tenth of a milligram. Indian soil holds little iodine, so the food grown on it holds little too, and iodised salt fills the gap. This entry in the minerals section of the handbook covers the requirement, the salt standard, the survey figures and the national programme.

What does iodine do in the body?

It is the raw material for the two thyroid hormones, thyroxine (T4) and triiodothyronine (T3). The joint FAO and WHO report on vitamin and mineral requirements states that making these hormones is the only physiological role known for iodine in the human body. These hormones regulate metabolism and the development of the foetus and infant. Iodide from food and water is absorbed almost completely, the thyroid takes what it needs, and most of the rest leaves in the urine.

That last fact is how iodine is measured. Because most dietary iodine ends up in urine, WHO uses the median urinary iodine of many samples to judge a population, not a person: 100 to 199 mcg per litre is adequate for school-age children and adults, and 150 to 249 mcg per litre for pregnant women. Thyroid blood tests such as TSH, T4 and T3 measure how the gland is working, which is a different question and one for a doctor to read.

How much iodine do you need under the Indian values?

An adult needs 140 mcg a day on ICMR-NIN's recommended allowance, with an estimated average requirement of 95 mcg. The expert group worked from studies of how much radioactive iodine a healthy thyroid takes up and from balance studies, set the average at 95 mcg, added a margin for variation to reach 133 mcg and rounded it to 140. The need rises in pregnancy and again in lactation, when the mother supplies the baby's iodine as well as her own.

One discrepancy is worth knowing. The expert group's shorter brief note prints 150 mcg for adults, the 2010 figure, while the summary report gives 140 mcg; this entry uses the summary report. The adult upper limit of 1,100 mcg was taken from the United States Institute of Medicine's 2001 value and scaled down by body weight for children.

Why is Indian food low in iodine?

Because the iodine has been washed out of the soil. The FAO and WHO report explains that the iodine content of food depends on the soil it grew in, and that glaciation and repeated flooding leach iodine from the upper crust and carry it to the sea. A 2013 review in the Indian Journal of Medical Research put it bluntly: the entire population of India is prone to iodine deficiency disorders because the soil of the subcontinent, and so the food derived from it, is deficient.

The sea is where the iodine went, so seafood is the one naturally rich food group. In the FAO and WHO table of average iodine content, marine fish and shellfish stand at about 800 units against 30 for freshwater fish, 47 for milk and for cereal grains, 93 for eggs and 30 for legumes, with a warning that the averages shift with local soil. The Indian Food Composition Tables 2017 give no iodine figures, which is why this entry has no table of Indian foods and the sodium table is the nearest the food pages come to salt.

Iodised salt in India: FSSAI's standard and what a teaspoon supplies

FSSAI's Fortification of Foods Regulations require iodised salt to contain 15 to 30 parts per million of iodine on a dry weight basis, added as potassium iodate. That single range has applied since an amendment that came into force on 27 August 2021; before it, the standard asked for 20 to 30 ppm at the factory and 15 to 30 ppm in the shop. A separate FSSAI regulation prohibits the sale of common salt for direct human consumption unless it is iodised.

One part per million is one microgram in each gram, so the arithmetic is simple. ICMR-NIN's 2024 Dietary Guidelines cap added salt at 5 g a day, about one teaspoon, and tell readers to use iodised salt. The table shows what different amounts supply at the two ends of the legal range, before any loss in storage or cooking.

At the legal minimum, a person who keeps to 5 g of salt gets 75 mcg, short of the adult average requirement, and depends on milk, eggs, fish and other foods for the rest; at the top of the range the same teaspoon covers the allowance. The answer is not more salt. It is salt that is properly iodised and stored, which the sodium entry discusses from the other side.

How many Indian households use iodised salt?

Almost all of them, on the test the National Family Health Survey uses. NFHS-5, in 2019-21, tested cooking salt for the presence of iodine and found it in 94 per cent of households, against 93 per cent in 2015-16. Coverage was 97 per cent in urban and 93 per cent in rural households, and rose from 91 per cent in the poorest fifth to 97 per cent in the richest. Among the states, Andhra Pradesh was lowest at 83 per cent, with Meghalaya at 91 and Tamil Nadu and Uttar Pradesh at 92; Kerala and Tripura stood at 99.

Presence is not the same as enough, because the NFHS kit shows whether iodine is there and not how much. The India Iodine Survey of 2018-19 measured the amount by titration in salt from 21,406 households across every state and union territory, and found 76.3 per cent at 15 ppm or more, with Jammu and Kashmir highest and Tamil Nadu lowest. Roughly one household in four was using salt below the standard.

India's national iodine programme, from Kangra to the present

India was one of the first countries to act on iodine through salt. From 1956 a study in the Kangra Valley of Himachal Pradesh, where goitre affected 40 per cent of people, gave some zones iodised salt and showed goitre falling in them. On that evidence the government began the National Goitre Control Programme in 1962. Iodisation of all edible salt began in phases from 1986, and in 1992 the scheme was renamed the National Iodine Deficiency Disorders Control Programme to cover the full range of harm.

The programme's stated goals are to bring the prevalence of iodine deficiency disorders below 5 per cent and to have every household use salt with at least 15 ppm of iodine. It works through district surveys, resurveys every five years, laboratory checks of salt and urine, and public education. The ban on selling non-iodised salt for eating had a halting start: notified in 1997, withdrawn in 2000 and reinstated in 2005.

Too little iodine: goitre, pregnancy and the child's brain

When intake falls very low, to roughly 10 to 20 mcg a day according to the government briefing, the thyroid cannot make enough hormone and hypothyroidism follows, often with a goitre, the swelling of the gland in the neck that is usually the earliest visible sign. The harm that matters most is less visible. Severe deficiency in pregnancy can cause miscarriage, stillbirth and cretinism, a permanent condition of intellectual disability, deaf mutism and stunted growth. WHO adds that even less severe deficiency may cause mental impairment that lowers intellectual capacity.

Milder deficiency in children is associated with lower scores on tests of mental development. The people most exposed in India are pregnant and breastfeeding women, whose requirement is highest, infants and young children, and households that buy loose or poorly iodised salt. The pregnancy diet guide places iodised salt beside the other nutrients that need attention in those months.

What does the evidence say about iodine and salt iodisation?

For deficiency and the developing brain the evidence is consistent in direction but weak in design. A 2013 systematic review of studies in children aged five and under found iodine-deficient children scoring 6.9 to 10.2 IQ points lower than iodine-replete children, across trials and cohort studies alike. The authors listed small samples and missing confounders among the weaknesses.

For iodine tablets in pregnancy the evidence is thin. The Cochrane review of 2017 found 14 studies, with 11 trials and over 2,700 women contributing data, almost all from places with mild to moderate deficiency, and concluded that there were insufficient data to reach any meaningful conclusion on the benefits and harms of routine supplementation. That is a statement about tablets, not about iodised salt, which remains the strategy WHO prefers for whole populations.

For India the best recent evidence is the 2018-19 survey: a national median urinary iodine of 178.0 mcg per litre in women who were neither pregnant nor breastfeeding, 173.4 in pregnant women and 172.8 in lactating women, each within the range WHO classes as adequate. A median says nothing certain about one person, but it shows the programme reaching most women.

Does cooking destroy the iodine in salt?

Some is lost, but most survives. An Indian laboratory study heated salt iodised with potassium iodate in steps up to 350 degrees Celsius and measured a gradual loss that reached a maximum of 18.5 per cent. The FAO and WHO report gives a wider estimate for real cooking, 20 to 40 per cent depending on the method, and names poor packaging, humidity and sunlight in transport as further causes of loss, which is why producers add more than the bare minimum.

A worked example: one teaspoon of salt against the requirement

This is an illustration, not a real person. Take a 34-year-old schoolteacher in Kolkata who has cut her added salt to the advised 5 g a day. If the packet in her kitchen sits at 30 ppm, the day's salt carries 150 mcg of iodine; if it sits at the legal minimum of 15 ppm, 75 mcg. Apply the 20 to 40 per cent cooking loss that FAO and WHO describe, and the first packet delivers 90 to 120 mcg and the second 45 to 60 mcg.

Set those against her average requirement of 95 mcg and allowance of 140 mcg. Well-iodised salt nearly covers her needs alone, and fish, milk and eggs can supply the rest. Minimum-level salt leaves her dependent on those foods, and if half her salt were unlabelled rock salt with no iodine added, the contribution would halve again. The label and the storage matter more than the quantity, and pregnancy, at 220 mcg, leaves much less room for a weak packet.

Common mistakes and myths about iodine and salt

The second mistake is to assume that cutting salt for blood pressure means giving up iodine; the guidelines ask for both, no more than 5 g and iodised. The third is to treat iodine as a thyroid tonic and take kelp or iodine drops without advice. The fourth is to blame cabbage and cauliflower. Goitrogens matter where a staple such as cassava dominates the diet, as the FAO and WHO report describes, a point the article on foods and hypothyroidism takes further.

Too much iodine, thyroid conditions and when to see a doctor

More is not better. ICMR-NIN's upper limit is 1,100 mcg a day for adults and far lower for children, 200 mcg at 1 to 3 years. Iodised salt eaten within the salt limit cannot approach the adult figure, as the table above shows; excess comes mainly from supplements and seaweed products. WHO classes a population median urinary iodine of 300 mcg per litre or more as excessive, with a risk of iodine-induced hyperthyroidism and autoimmune thyroid disease, and the Cochrane review recorded digestive intolerance among pregnant women given iodine tablets.

Iodine is not a treatment for a thyroid disorder that has already been diagnosed, and nothing in this entry is a reason to start, stop or change thyroid medicine. Diagnosis rests on examination and blood tests that a doctor orders and interprets. For what eating well looks like alongside medical care, the guide to diet in hypothyroidism is the place to continue.

Learning this properly

Salt iodisation is a standard case study wherever NNWA teaches fortification and public programmes. The academy is private, based in Kolkata, and teaches online in English and Hindi. Its courses are skill courses that prepare people to coach healthy clients and refer medical cases; none is a degree or a dietitian qualification. The Public Health Nutrition course looks at how programmes of this kind are planned and measured.