Four Decades of Universal Salt Iodisation in India: Thyroid Autoimmunity Rising — Study

by Ashis Sinha

A new ICMR-SALT-T 1 study finds iodine nutrition adequate and goitre declining among Indian schoolchildren, but thyroid autoimmunity and subclinical hypothyroidism remain concerns.

A nationwide study published in The Lancet Regional Health – Southeast Asia has found that India’s four-decade-old Universal Salt Iodisation (USI) programme has substantially improved iodine nutrition and reduced goitre among schoolchildren, but thyroid autoimmunity and thyroid-function abnormalities remain important concerns.

The multicentre ICMR-SALT-T 1 study assessed 8,903 schoolchildren aged 10–18 years across eight centres in different regions of India. Researchers examined goitre prevalence, thyroid function, thyroid antibodies and urinary iodine levels to assess the long-term impact of salt iodisation.

Goitre declines, but has not disappeared

The study found that the overall prevalence of goitre among the children was 10.3%, with 98.6% of cases classified as Grade I goitre. This represents a continued decline from earlier nationwide assessments, which had reported goitre prevalence of about 23.5% and 17.6% in earlier decades following the introduction of iodisation.

The researchers said the downward trend indicates a positive long-term impact of USI. However, the persistence of mild goitre suggests that thyroid health remains influenced by factors beyond iodine intake alone.

Girls had about twice the adjusted odds of having goitre compared with boys, while obesity was also associated with a higher likelihood of goitre. Children who tested positive for anti-thyroid peroxidase (anti-TPO) antibodies were also more likely to have goitre.

Iodine nutrition now largely adequate

The study found a median urinary iodine concentration (MUIC) of 133.2 µg/L, placing the surveyed population within the range considered adequate for iodine nutrition.

More than 90% of participating households reported using iodised salt, while laboratory testing of 1,615 salt samples found that 89% contained more than 15 ppm of iodine. These findings indicate broad household access to adequately iodised salt.

The results are consistent with earlier Indian evidence showing that the shift towards iodine sufficiency following USI has changed thyroid physiology. An AIIMS study, for example, found substantially lower radioactive iodine uptake in iodine-sufficient individuals compared with historical Indian reference values established during the iodine-deficiency era.

Thyroid autoimmunity emerges as a key concern

One of the most notable findings was the prevalence of anti-TPO antibodies, a marker associated with thyroid autoimmunity.

Among 5,726 children tested for thyroid antibodies, 10.4% were anti-TPO positive. The prevalence was significantly higher among girls, while children with goitre were also more likely to test positive.

However, the study provides an important qualification: the findings do not establish that iodised salt itself is causing thyroid autoimmunity. The researchers identify the relatively high prevalence of thyroid autoimmunity as an issue requiring continued observation and future longitudinal research.

Interestingly, the proportion of children with high anti-TPO titres (≥102 IU/mL) was 2.7%, compared with 2.3% reported in a 2012 survey—a difference that was not statistically significant. Thus, the broader anti-TPO positivity finding should not simply be interpreted as proof of a continuing sharp rise in clinically significant autoimmune thyroid disease.

Subclinical hypothyroidism found in 13%

Thyroid-function testing was available for 5,512 children. Researchers found subclinical hypothyroidism (SCH) in 13% of them.

The likelihood of SCH was higher among children who were overweight or obese, those with goitre and those who were anti-TPO positive. Overt hypothyroidism was considerably less common, occurring in 1.4% of children with goitre and 0.3% of those without goitre. Hyperthyroidism was uncommon.

The association between anti-TPO positivity and SCH is particularly significant because thyroid autoantibodies can indicate an underlying autoimmune process that may affect thyroid function over time. But because the present research was cross-sectional, it cannot determine whether antibody positivity will subsequently progress to overt thyroid disease.

A public-health success story—with a new monitoring challenge

India began its national iodine-deficiency-control efforts decades ago and subsequently made universal salt iodisation the central strategy for tackling iodine-deficiency disorders. The Indian Thyroid Society has described USI as a major public-health success, while also emphasising the need for continued monitoring of iodine levels and coordination with efforts to reduce overall salt consumption.

The new study broadly reinforces that assessment: iodine deficiency is no longer the dominant picture among the surveyed schoolchildren, and goitre prevalence has fallen substantially.

At the same time, the relatively high prevalence of anti-TPO positivity and subclinical hypothyroidism means that thyroid health cannot be assessed through iodine status alone.

Previous research has also shown that the relationship between iodine intake and autoimmune thyroid disease is complex. A systematic review of studies following salt-iodisation programmes found that thyroid-antibody positivity can increase during the transition from iodine deficiency to sufficiency in some populations, while longer-term studies have also reported stabilisation or declines.

What the study means

The findings point to a changing public-health challenge. The priority is no longer simply to eliminate iodine deficiency, but to maintain adequate iodine nutrition while continuously monitoring thyroid health.

The researchers conclude that India has achieved substantial progress through USI, but the persistence of goitre and the prevalence of thyroid autoimmunity and thyroid-function abnormalities warrant further follow-up.

For policymakers, the message is therefore one of continued surveillance rather than a reversal of iodisation policy. For the scientific community, the study highlights the need for longer-term research to determine how many children with anti-TPO positivity or subclinical hypothyroidism eventually develop clinically significant thyroid disease.

The study was supported by the Indian Council of Medical Research (ICMR) through its Investigator-Initiated Research Project programme.