Iodine deficiency disorders comprise a spectrum of conditions, from goitre and hypothyroidism to cretinism, stillbirth and impaired mental development, that result from inadequate intake of iodine [1]. Iodine deficiency is the most common preventable cause of brain damage; a meta-analysis of studies from China showed that children living in iodine-deficient areas had a mean intelligence quotient about 12 points lower than those in iodine-sufficient areas [2], and iodine deficiency also impairs neuropsychological development [3]. Even mild to moderate deficiency during pregnancy and childhood can impair growth and cognition [4], and damaged reproduction is regarded as its most important consequence [5,6]. Iodine supplementation improved cognition in iodine-deficient schoolchildren [7].

Universal salt iodization is the recommended strategy for the elimination of iodine deficiency disorders. Global progress has been substantial, but nearly 2 billion people were estimated to have insufficient iodine intake, and the proportion of households consuming iodized salt remained below the goal in many countries [8-10]. Mandatory iodization has been shown to improve the iodine and goitre status of schoolchildren quickly [11]. Programmes must be sustained, because complacency and weak monitoring can lead to a return of deficiency [12,13], and quality control is needed to avoid the rare risk of iodine-induced hyperthyroidism [14].

In India, the whole population is considered at risk of iodine deficiency [15]. The National Goitre Control Programme, renamed the National Iodine Deficiency Disorders Control Programme, adopted universal salt iodization, and the sale of non-iodized salt for human consumption has been banned. Surveys from different states nevertheless showed persistent goitre and iodine deficiency [16-22] and showed that only part of the salt consumed at household level was adequately iodized [23-25]. Poor and disadvantaged households, including those in urban slums, are less likely to use adequately iodized salt [26], and awareness of iodine deficiency disorders in the community is low [27]. Little information is available from rural Maharashtra. The objectives of this study were to estimate the proportion of rural households using adequately iodized salt, to assess awareness of iodine deficiency disorders and iodized salt, and to identify the factors associated with the use of adequately iodized salt.

Study design and setting This community-based cross-sectional study was conducted in the villages of the rural field practice area under the Rural Health Training Centre of the Department of Community Medicine, Dr. Vasantrao Pawar Medical College, Hospital & Research Centre, Nashik, Maharashtra. Verbal informed consent was obtained from the respondent in each household before the interview and salt testing. Sample size and sampling The sample size was calculated from an expected proportion of 43% of households using adequately iodized salt, as reported from a large survey in northern India [23]. With an absolute precision of 5% and a 95% confidence level, the formula n = Z² p (1 - p) / d² gave a minimum of 377 households, which was increased to 400 to allow for non-response. Households were selected from the villages by systematic random sampling using the household lists maintained at the sub-centres. One household was the sampling unit, and the person mainly responsible for cooking was interviewed. Locked households and those that did not consent were replaced by the next household. Data collection Trained interviewers visited each household and used a pre-designed and pre-tested questionnaire. Information was collected on the socio-demographic characteristics of the family, socioeconomic status by the modified B. G. Prasad classification, the type of salt used (packaged or loose, crystal or powdered), the place of purchase, the method of storage (closed container, open container or original packet, and distance from the fire) and the stage at which salt was added during cooking. Awareness was assessed with questions on whether the respondent had heard of iodized salt, knew why salt is iodized, knew that iodine deficiency causes goitre and other disorders, could recognise the iodized salt logo, and checked for iodization when buying salt. Estimation of iodine content A teaspoon of salt was collected from the container in current use in each household and tested on the spot with a rapid spot testing kit, which has been validated against iodometric titration in India [28]. A drop of the test solution was added to the salt, and the colour that developed within one minute was compared with the colour chart supplied with the kit. The iodine content was recorded as 0 ppm (no colour), less than 15 ppm, or 15 ppm or more. Salt with an iodine content of 15 ppm or more was considered adequately iodized, in line with the national standard for iodine content at consumer level. Each household was given information on the importance of iodized salt after the test. Statistical analysis Data were entered in Microsoft Excel and analysed with Python version 3.13 using the SciPy and statsmodels libraries. Results were expressed as numbers and percentages with exact 95% confidence intervals. The association of adequately iodized salt with socio-demographic factors, type of salt, purchase and storage practices and awareness was tested with the chi-square test, and crude odds ratios with 95% confidence intervals were calculated. Variables with p < 0.20 on univariate analysis were entered into a multivariable logistic regression model, and results were expressed as adjusted odds ratios (aOR) with 95% confidence intervals. A p-value below 0.05 was considered significant.

A total of 400 households were studied. The respondent was a woman in 83.5% of households, and the mean age of the respondents was 45.2 ± 16.0 years. A total of 92 respondents (23.0%) were illiterate, 56.0% of households belonged to socioeconomic class IV or V, and agriculture was the main occupation in 62.0% (Table 1).

Table 1. Socio-demographic characteristics of the households (n = 400)

Socioeconomic class by modified B. G. Prasad classification.

Adequately iodized salt (15 ppm or more) was used by 197 households (49.2%, 95% CI 44.2 to 54.3), inadequately iodized salt (less than 15 ppm) by 104 (26.0%) and salt with no iodine by 99 (24.8%). Packaged powdered salt was used by 52.5% of households, loose crystal salt by 28.5% and loose powdered salt by 19.0%. Adequately iodized salt was found in 68.1% of packaged samples but only 28.4% of loose samples (p < 0.001), and 40.0% of loose samples contained no iodine (Table 2).

Table 2. Iodine content of household salt by type of salt

Iodine content estimated with a rapid spot testing kit. ppm: parts per million. Chi-square test for adequately iodized salt, packaged versus loose: p < 0.001.

Salt was purchased from a local grocery shop by 73.8% of households and from weekly markets or vendors by 26.2%; all packaged salt was bought from grocery shops. Salt was stored in a closed container in 58.5% of households, and 29.0% kept it near the cooking fire. Salt was added at the beginning of cooking in 45.2% of households. Adequately iodized salt was more common in households that stored salt in closed containers than in those that used open containers or the original packet (53.8% versus 42.8%, p = 0.029) (Table 3).

Table 3. Purchase and storage practices and use of adequately iodized salt

Percentages in the third column are of households with that practice. Chi-square test.

Only 47.5% of respondents had heard of iodized salt, 31.2% knew why salt is iodized, and 23.8% knew that iodine deficiency causes goitre. Knowledge of its effects on the mental development of children (12.8%) and on pregnancy outcome (10.0%) was even lower. The iodized salt logo was recognised by 20.2%, and only 15.8% checked whether salt was iodized at the time of purchase (Table 4).

Table 4. Awareness of iodized salt and iodine deficiency disorders (n = 400)

On univariate analysis, use of adequately iodized salt was significantly associated with packaged salt (OR 5.38), purchase from a grocery shop, socioeconomic class I-III, storage in a closed container and agricultural occupation, but not with literacy of the respondent (p = 0.688) or with having heard of iodized salt (p = 0.474) (Table 5). On multivariable analysis, packaged salt (aOR 7.56, 95% CI 4.12 to 13.89; p < 0.001), storage in a closed container (aOR 1.62, 95% CI 1.04 to 2.53; p = 0.033) and agricultural occupation (aOR 1.66, 95% CI 1.05 to 2.60; p = 0.028) remained independently associated with adequately iodized salt. Socioeconomic class and place of purchase were not significant after adjustment for the type of salt (Table 6).

Table 5. Univariate analysis of factors associated with use of adequately iodized salt

Chi-square test. OR: odds ratio; CI: confidence interval.

Table 6. Multivariable logistic regression of factors associated with use of adequately iodized salt

Variables with p < 0.20 on univariate analysis were entered into the model. Model fit: Hosmer-Lemeshow p = 0.60.

In this rural community, only 49.2% of households used adequately iodized salt, far below the goal of more than 90% of households, and about one in four used salt with no iodine at all. Awareness of iodine deficiency disorders was poor. Use of packaged salt and storage in a closed container were the main factors associated with adequately iodized salt. The proportion of households using adequately iodized salt in our study is similar to that found in other Indian studies. In selected districts of Uttar Pradesh, only 43% of household salt samples had 15 ppm or more of iodine [23], and low use of iodized salt was found in the Tarai region of northern India [24], in Bihar [25] and in slum households in Delhi [26]. Surveys in West Bengal, Himachal Pradesh, Uttar Pradesh and other states showed that goitre and iodine deficiency persisted even where iodized salt was available [16-22]. Globally, household coverage with iodized salt improved during the last decade but remained below the goal in many countries [8,9]. The type of salt was the strongest determinant of iodine content. Loose salt, which is cheaper and sold by local vendors and in weekly markets, was adequately iodized in only 28.4% of households, compared with 68.1% for packaged salt, and the odds of adequate iodization were about seven times higher with packaged salt after adjustment for other factors. This reflects the continued supply of non-iodized or poorly iodized loose salt in rural markets despite the ban. Even among packaged salt, almost one third of samples had less than 15 ppm of iodine, which may be due to inadequate iodization at production or loss of iodine during transport and storage. Iodine is lost from salt exposed to moisture, heat and air and during cooking [29,30], and in our study storage in a closed container was independently associated with adequate iodine content. The higher use of adequately iodized salt in agricultural households was unexpected and may reflect local purchasing patterns; it needs confirmation in other studies. Awareness of iodized salt and iodine deficiency disorders was poor, as in a knowledge-attitude-practices study from Orissa [27]. Fewer than one in seven respondents knew that iodine deficiency affects the mental development of children or the outcome of pregnancy, which are its most serious consequences [4-6]. Interestingly, neither awareness nor literacy was associated with the use of adequately iodized salt in our study, and the association with socioeconomic class disappeared after adjustment for the type of salt. This suggests that the choice of salt in rural households is driven mainly by price and availability rather than knowledge, so that health education alone will not be enough without ensuring that only iodized salt is available in the market. Poor households have been shown to have less access to adequately iodized salt [26]. These findings have implications for the National Iodine Deficiency Disorders Control Programme. The ban on the sale of non-iodized salt must be enforced in rural markets, and the quality of salt at the point of sale should be monitored. Monitoring of salt at household level with spot testing kits is simple and can be done by health workers and schoolchildren [28]. Programmes must guard against complacency once coverage improves [12,13], while maintaining quality control of iodization [14]. Strengths and limitations The strengths of this study are its community-based design, random selection of households and on-the-spot testing of the salt in actual use. It has limitations. The spot testing kit gives a semi-quantitative estimate, and iodometric titration was not done to confirm the results. Urinary iodine and goitre prevalence were not measured, so the iodine status of the population could not be assessed directly. The study was limited to one rural area, and the findings may not apply to other regions.

Only 49.2% of rural households used adequately iodized salt, and awareness of iodine deficiency disorders and iodized salt was poor. Loose salt and storage in open containers were associated with inadequate iodine content, whereas awareness and literacy were not. Strict enforcement of the ban on non-iodized salt in rural markets, regular monitoring of household salt and health education on the purchase and storage of iodized salt are needed to achieve the elimination of iodine deficiency disorders.

DECLARATIONS

Acknowledgement: The author thanks the faculty, interns and staff of the Department of Community Medicine and the Rural Health Training Centre, Dr. Vasantrao Pawar Medical College, Hospital & Research Centre, Nashik, and all the households that took part in the study.

Funding: None.

Conflict of interest: The author declares no conflict of interest.

Author contribution: Dr. Surjuse Bhooshan Ganpatrao designed the study, supervised data collection, analysed the data, wrote the manuscript and approved the final version.

Data availability: The data supporting the findings of this study are available from the corresponding author on reasonable request.