2. Association between Household Unavailability of Iodized Salt and Child Growth –
2.3 Results
2.3.2 Association between the Unavailability of Iodized Salt and Child Growth
unavailability of iodized salt and child stunting, underweight and wasting for the full sample, and for severe stunting, underweight and wasting as alternative outcome variables, respectively. In models that were only adjusted for PSU fixed effects (unadjusted model), the unavailability of iodized salt was associated with 7.7% higher odds of being stunted, 11.6% higher odds of being underweight and 7.1% higher odds of being wasted (95% CIs of ORs: 1.05, 1.11; 1.08, 1.15; and 1.03, 1.12, respectively; P-value < 0.01 all three outcomes). In models that were adjusted for a full set of covariates (adjusted model) and PSU fixed effects, unavailability of iodized salt was
Availability of iodized salt in the household, % (N = 298,743)
Severe underweight 16.0 17.1+
Wasting 9.6 11.0+
Severe Wasting 11.1 10.7
Low birth weight 10.3 13.1+
N denotes the number of observations in the stunting sample. For other samples, total numbers of observations were slightly different as follows: underweight, N = 397,080; wasting, N = 384,163; and low birth weight, N = 196,238. Values were population weighted. + Proportions in the two groups were significantly different from each other (P-value ≤ 0.05).
associated with 2.9% higher odds of being stunted (95% CI: 1.00, 1.06; P-value: 0.04), 5.4%
higher odds of being underweight (95% CI: 1.02, 1.09; P-value < 0.01), and 3.4% higher odds of being wasted (95% CI: 0.99, 1.08; P-value: 0.12), whereas only stunting and underweight were significant at the 5% and 1% levels, respectively. Results for the covariates are reported in the appendix 2.A in table 2.A.3. After adjustment, results for severe undernutrition were not statistically significant (Table 2.3).
Results for different age groups are reported in the appendix 2.A table 2.A.4. In the fully adjusted model, the associations between the unavailability of iodized salt and stunting and underweight were quantitatively stronger in children between 24 and 59 months of age than in the reference category of children between 0 and 5 months of age and were not statistically significant for wasting. In children between 6 and 23 months of age, the association was quantitatively stronger for wasting than for the reference category of children between 0 and 5 months and not statistically significant for stunting and underweight.
Table 2.2: Association between unavailability of iodized salt within a household and growth failure (z-scores
<-2) of children under the age of 5 for the full sample
Unadjusted Adjusted
Stunting Underweight Wasting Stunting Underweight Wasting
(1) (2) (3) (4) (5) (6)
Full sample
Absence of iodized salt (OR) 1.08*** 1.12*** 1.07*** 1.03** 1.05*** 1.03
95% CI [1.05,1.11] [1.08,1.15] [1.03,1.12] [1.00,1.06] [1.02,1.09] [0.99,1.08]
P-value (<0.01) (<0.01) (<0.01) (0.04) (<0.01) (0.12)
N 349,341 294,835 215,208 349,341 294,835 215,208
PSU fixed effects Yes Yes Yes Yes Yes Yes
Associations were estimated by logistic regression models and odds ratios are shown in this table. 95% Confidence intervals (CI) are reported in brackets and p-values are reported in parentheses. Standard errors are clustered by the primary sampling unit. *** and ** denote significance at the 1% and 5% level, respectively.
Table 2.3: Association between unavailability of iodized salt within a household and severe growth failure (z-scores <-3) of children under the age of 5
Unadjusted Adjusted
Severe Stunting Severe
Underweight
Severe Wasting
Severe Stunting
Severe Underweight
Severe Wasting
(1) (2) (3) (4) (5) (6)
Absence of iodized salt (OR) 1.07*** 1.11*** 1.07** 1.01 1.04# 1.04
95% CI [1.03,1.10] [1.06,1.16] [1.01,1.14] [0.98,1.05] [0.99,1.09] [0.98,1.11]
P-value (<0.01) (<0.01) (0.03) (0.44) (0.09) (0.23)
N 280,453 190,427 127,317 280,453 190,427 127,317
PSU fixed effects Yes Yes Yes Yes Yes Yes
Associations were estimated by logistic regression models and odds ratios are shown in this table. 95% Confidence intervals (CI) are reported in brackets and p-values are reported in parentheses. Standard errors are clustered by the primary sampling unit. *** and ** denote significance at the 1% and 5% level, respectively. # denotes significance at the 10% level.
Table 2.4 shows results for low birth weight. In the unadjusted model unavailability of iodized salt was associated with 15.7% higher odds of being born with low birth weight (95%
CI: 1.09, 1.24; P-value < 0.01). In the adjusted model, the unavailability of iodized salt was associated with 9.1% higher odds of low birth weight (95% CI: 1.02, 1.17; P-value: 0.01). Both coefficients were significant. Both coefficients are statistically significant.
Table 2.4: Association between unavailability of iodized salt within a household and low birth weight
Unadjusted Adjusted
Low birth weight Low birth weight
Absence of iodized salt 1.16*** 1.09**
95 % CI [1.09,1.24] [1.02,1.17]
P-Value (<0.01) (0.01)
N 93,697 93,697
PSU fixed effects Yes Yes
Associations were estimated by logistic regression models and odds ratios are shown in this table. 95%
Confidence intervals (CI) are reported in brackets and p-values are reported in parentheses Standard errors are clustered by the primary sampling unit. *** and ** denote significance at the 1% and 5% level, respectively.
In Table 2.5, we report regression results with the use of z-scores and birth weight (in kg) as continuous dependent variables. The unavailability of iodized salt was associated with a 0.024-lower weight-for-age z-score (95% CI: 20.04, 20.01; P-value < 0.01;) and a 25-g lower birth weight (95% CI: 20.04, 20.01; P-value < 0.01). Results for height-for-age and weight-for-height were not statistically significant.
Table 2.5: Association between unavailability of iodized salt within a household and growth failure of children < 5 years old using z-scores and birth weight (in kg) as continuous dependent variables
Associations were estimated by ordinary least square models and marginal effects are shown in this table. 95% Confidence intervals (CI) are reported in brackets and p-values are reported in parentheses. Standard errors are clustered by the primary sampling unit. ***
and ** denote significance at the 1% and 5% level, respectively.
In a sensitivity analysis we adjusted for the consumption of food items such as fish, eggs, poultry, meat and fruits, which could potentially have contained some amount of iodine.
This adjustment resulted in the insignificance of all undernutrition indicators. However, this result might have been driven by the reduced sample (in this specification, the stunting sample consisted of only 144,316 children because of missing observations). The same was true when we controlled for maternal iron consumption. In addition, controlling for prenatal health care visits, controlling for multiple children in the household or including survey fixed effects instead of PSU effects did not change the results. The results of the sensitivity analysis are presented in the appendix 2.A tables 2.A.5–2.A.12. The exclusion of India from the sample removed the effect for all outcome variables except of low birth weight, and consideration of only the India sample gave the strongest associations (Tables 2.6 and 2.7); the unavailability of iodized salt was associated with 8.8% higher odds of being stunted (95% CI: 1.02, 1.17; P-value:
0.02), 15.8% higher odds of being underweight (95% CI: 1.08, 1.24; P-value < 0.01), and 10.6%
higher odds of being wasted (95% CI: 1.02, 1.20; P-value: 0.02) in the India only sample. The association with low birth weight was not statistically significant in the India sample.
Table 2.6: Association between unavailability of iodized salt within a household and growth failure of children < 5 years old with the exclusion of India from the sample
Adjusted
Stunting Underweight Wasting Low birth weight
(1) (2) (3) (4)
Absence of iodized salt 1.01 1.00 0.98 1.08**
95% CI [0.98,1.04] [0.97,1.04] [0.94,1.03] [1.00,1.17]
P-value (0.65) (0.95) (0.53) (0.05)
N 297,774 242,209 169,462 76,790
PSU fixed effects Yes Yes Yes Yes
Associations were estimated by logistic regression models and odds ratios are shown in this table. 95% Confidence intervals (CI) are reported in brackets and p-values are reported in parentheses. Standard errors are clustered by the primary sampling unit. *** and **
denote significance at the 1% and 5% level, respectively.
Table 2.7: Association between unavailability of iodized salt within a household and growth failure of children < 5 years old with only India included
Adjusted
Stunting Underweight Wasting Low birth weight
(1) (2) (3) (4)
Absence of iodized salt
1.09** 1.16*** 1.11** 1.10
95% CI [1.02,1.17] [1.08,1.24] [1.02,1.20] [0.97,1.25]
P-value (0.02) (<0.01) (0.02) (0.142)
N 51,567 52,571 45,744 16,907
PSU fixed effects Yes Yes Yes Yes
Associations were estimated by logistic regression models and odds ratios are shown in this table. 95% Confidence intervals (CI) are reported in brackets and p-values are reported in parentheses. Standard errors are clustered by the primary sampling unit. *** and **
denote significance at the 1% and 5% level, respectively.