Re: Urinary iodine excretion: A valuable tool for monitoring salt iodisation programme

Kumari et al.¹ offer a valuable perspective by shifting the focus from school-based surveys to family-based monitoring of iodine status. Furthermore, the observation that double fortified salt (DFS) showed no significant difference in urinary iodine (UI) excretion compared to iodised salt (IS) provides critical reassurance for the implementation of the Anaemia Mukt Bharat strategy. However, a critical review of the methodology and data interpretation raises specific points that warrant further consideration.

First, regarding the statistical methodology, the authors appropriately reported median UI levels, acknowledging the typically non-normal distribution of UI data. However, the statistical significance of the differences between groups and time points was assessed using the Student’s t-test. The Student’s t-test is a parametric method that assumes a normal distribution of data. Applying this test to skewed datasets may result in inaccurate estimations of statistical significance. The use of non-parametric tests, such as the Mann-Whitney U test or the Wilcoxon signed-rank test, would be methodologically more appropriate for this dataset.

Second, the authors conclude that the decrease in median UI observed between 2019 and 2021 was likely due to the salt industry complying with revised Food Safety and Standards Authority of India (FSSAI) standards. While the methodology states that the quality of salt at the household level was closely monitored, the article does not present quantitative data regarding the iodine content (titration levels) of the salt actually consumed by the participants. Without correlating the iodine content of the salt directly with the UI levels, attributing the reduction in UI solely to FSSAI compliance remains speculative. Other factors, such as seasonal variability or hydration status during spot sampling, cannot be ruled out.

Third, the longitudinal design of study B was interrupted for 6 months due to the Covid-19 lockdown, during which families reverted to purchasing packaged market salt. Although the study restarted in October 2020, this disruption introduces an important confounding variable. It is unclear if the washout period was sufficient to negate the biological variance introduced by the change in salt source during the lockdown.

Finally, the sampling strategy involved collecting urine from ‘available and willing’ family members during morning home visits. This convenience sampling method carries a risk of selection bias, as it may under-represent working family members who are absent during forenoon hours.