India, Sept. 5 -- Salt is ordinary, cheap and ubiquitous - and for decades, it has been a delivery vehicle for iodine, a micronutrient essential for the physical health of mothers and children. Iodine deficiency in pregnancy and early childhood can cause irreversible intellectual impairment, stunting and still births. Even mild deficiency harms school performance and long-term human capital. India began systematic salt iodisation in the 1980s, and evidence shows that when population iodine intake falls, measurable declines in learning and public health follow.

Recently, this humble, household ingredient has become the subject of public debate.

In August, the Madras High Court heard a petition filed by a trade association of salt produce...