The study was a cross-sectional observational study of the usual practice of growing, processing, and cooking rice with dietary and nutritional status assessments carried out on children in the rice-producing communities. Four villages in different districts were selected for the study to obtain a range of soil types from the fourteen villages that formed part of the National Nutrition Survey of Bangladesh, organized through the University of Dhaka.17 A random sample of 40 households was chosen from the census list in each village. The number of households was based on practical considerations and the need to collect sufficient rice samples for differences in zinc content across villages. Each household had at least one child aged 2 to 10 years and agreed to participate in the study. The purpose was explained to the household head or spouse and consent was obtained. Ethical approval was obtained from the Cornell University Committee on Human Subjects and from the University of Dhaka. Fieldwork was carried out in May and October-November 2000 before the start of Ramadan, the Muslim month of fasting.
Both zinc and phosphorus contents were analyzed for all the rice samples collected. We were not able to analyze phytate, but have used the phosphorus content as an indicator for phytate content.
1. Agricultural Production and Zinc and Phosphorus Content of Un-Polished (Paddy) Rice Soil and rice samples were collected from the boro and Aman seasons from four survey villages and surrounding areas; these additional sites were sampled to obtain geographical variation in soils. The rice varieties collected provided genetic variability. During the harvest, farmers were interviewed in their fields and identified the variety of rice. All the rice was harvested from a 1m2 plot from the centre of each field, mixed, dried, winnowed, and weighed to assess yield. A sample of approximately 50g rice was retained for chemical analysis. The soil inside the 1m2 harvest area was sampled using a soil auger to a depth of 15 cm. Ten samples were taken, mixed, then air-dried, and a sample saved for analysis. The soil samples were analyzed for available zinc content and pH. The number of soil and rice samples collected was driven by practical considerations of time constraints rather than statistical considerations because the magnitude of variability was not known in advance. It was not possible to obtain samples from the same farmer for both seasons. Multiple regression analysis was used to test the effects of soil available zinc and pH on rice zinc content
2. Changes in Zinc and Phosphorus After Milling To measure the impact of milling on zinc and phosphorus content of rice, we collected 50g samples before and after milling from the study households and local mills in matched pairs of the same variety of rice and the same household. Each time the rice was well mixed before taking the sample. The analysis is restricted to samples from two villages where there was a local mill and hence sufficient samples.
3. Changes in Zinc and Phosphorus After Cooking Samples of polished rice before and after cooking matched by household and variety were collected from the sample households during the first visit in May. The samples collected at this time were predominantly from the previous Aman harvest. For this analysis, we aimed for 20 samples from the survey households in each village. Some samples were spoiled and could not be analyzed, therefore the final sample size was 73 from 4 villages. The person responsible for cooking in each household was asked about the source of water and whether any water remained after cooking rice, and if so what was done with the water.
4. Village Differences in Zn and P Content of Polished Rice A sample of polished rice was collected from each household at the time of the dietary survey and the rice compositional analysis was used to individualize zinc intake from rice for each household. The respondent was asked to identify the variety of each sample of rice.
5. Dietary Intake of Zinc Related to the Zinc Content of Rice In each household, the person responsible for cooking meals was interviewed during our second visit in October-November 2000. The 24- hour recall questionnaire format was provided by the International Food Policy Research Institute and was previously field-tested. Trained enumerators conducted the interviews in Bangla. The respondent recalled all the raw ingredients of each dish (including rice) that were used to prepare the meals the previous day and the proportion of each cooked dish allocated to each household member. Adjustments were made for changes in the weight of foods on cooking.18 Household measures were used for the recall and then converted to gram equivalents. The dietary intake was then calculated for each household member in the household at the time of the survey.
6. Zinc Nutritional Status of Children Related to Zinc Content of Rice Hair samples were collected from a maximum of 2 children aged 2- 10 yrs from each household. Hair zinc was used as a long-term indicator of zinc status. A sample of hair was cut from behind the occipital bone of the children’s head close to the skull in lengths of 5 cm. For children whose hair had recently been cut, shorter lengths were taken from a wider area. Exogenous sources of zinc were removed before analysis by washing in acetone. We were not able to collect serum samples due to the practical constraints of transport, lack of electricity, and the consent required for an invasive procedure with no beneficial intervention.
Statistical Analysis. Data were analyzed using SPSS22 for the majority of analyses. SAS23 was also used for the calculation of daily nutrient intakes. The student’s t-test was used for the differences in the means of rice samples. Pearson correlation coefficients were used for correlation analyses. Anthropometric indices were calculated using Epi-Info 6. General linear models were used for the analysis of the association of multiple predictors and an outcome variable.