WHEN A 307945 P

A Food-Based Approachto Improving Zinc Nutrition

Through Increasing the Zinc Contentof Rice in Bangladesh

Anne-Marie B. Mayer, PhDMichael C. Latham, OBE, MD, MPH, FFCM, DTM&H

John M. Duxbury, PhDNazmul Hassan, PhD, MA, MF

Edward A. Frongillo, PhD

ABSTRACT. Improvements in micronutrient content or bioavailabilityof staples can impact diet. We aimed to assess variability of rice zinc atfield, household, and village levels, and its association with dietary zincand nutritional status of children. Rice samples were collected from

Anne-Marie B. Mayer, PhD, is Nutrition and Health Research Advisor, Save the Chil-dren, UK, PO Box 7165, Addis Ababa, Ethiopia (E-mail: [email protected] [email protected]).

Michael C. Latham, OBE, MD, MPH, FFCM, DTM&H, is Graduate School Profes-sor of International Nutrition, Division of Nutritional Sciences Savage Hall, CornellUniversity, Ithaca, NY 14853 (E-mail: [email protected]).

John M. Duxbury, PhD, is Professor, Department of Crop and Soil Sciences, Cor-nell University, Ithaca, NY 14853 (E-mail: [email protected]).

Nazmul Hassan, MA, MS, PhD, is Professor, Institute of Nutrition and Food Sci-ence, University of Dhaka, Bangladesh (E-mail: [email protected]).

Edward A. Frongillo, PhD, is Professor and Chair, Department of Health Promo-tion, Education, and Behavior, University of South Carolina, Columbia, SC 29208(E-mail: [email protected]).

The authors acknowledge the financial support of United States Agency for Interna-tional Development, Soil Management Collaborative Support Programme.

Journal of Hunger & Environmental Nutrition, Vol. 2(1) 2007Available online at http://jhen.haworthpress.com

© 2007 by The Haworth Press. All rights reserved.doi:10.1300/J477v02n01_03 19

farmers and 156 households in 4 villages in Bangladesh. Hair sampleswere used to assess zinc nutritional status. Soil pH, soil zinc, and rice va-riety were associated with rice zinc content. In 2 villages milling lossesof zinc were very different: 24±10% and 39±11% (p < 0.001). Rice sup-plied 66±16% of zinc in the diet of 2-10 yr old children. Dietary zincdensity was 1.00±0.24 and 1.35±0.24 mg/1000kJ (p < 0.001) respec-tively in the village with the lowest compared to the highest rice zinc.Hair zinc was positively associated with rice zinc (r = 0.24 p = 0.001)suggesting improvements to the nutrient content of rice could result innutritional benefit. Optimizing rice zinc through choice of varieties, soilmanagement, and processing could improve zinc nutrition in Bangla-desh. doi:10.1300/J477v02n01_03 [Article copies available for a fee from TheHaworth Document Delivery Service: 1-800-HAWORTH. E-mail address:<[email protected]> Website: <http://www.HaworthPress.com> © 2007by The Haworth Press. All rights reserved.]

KEYWORDS. Zinc, rice, dietary zinc, rice processing, soil zinc, Ban-gladesh, rice varieties, zinc nutritional status

INTRODUCTION

Children are particularly vulnerable to micronutrient deficiencies incountries that rely on one staple crop (such as rice in Bangladesh) whenconsumption of meat and vegetables is also low. Under such circum-stances, any improvements in the micronutrient content or bio-avail-ability of that staple will have a large effect on the nutritional adequacyof the diet. Here we take the example of zinc in rice to illustrate thispoint. This approach leads to recommendations improve the zinc con-tent of rice by methods that may be applied at the community and house-hold level, for example changes in the way rice is grown, processed, andcooked. By collecting a series of samples from soil to plate, we examinewhere, under field conditions, the opportunities exist for communitiesto optimize the zinc content of rice.

We focus on zinc, a nutrient that is likely to be deficient in diets inBangladesh. In an analysis of the global food supply, South Asia wasthe worst region for zinc deficiency, with only 47% of the requirementmet.1 Zinc is required for general growth and maturation, for immunefunction, and deficiency can contribute to severity of diarrhoea.2 It is

20 JOURNAL OF HUNGER & ENVIRONMENTAL NUTRITION

therefore of great importance in the diets of young children in Bangla-desh who are prone to stunting, diarrhoea and other infections.3

Improving the nutrient content of rice may be achieved through se-lection of particular varieties,4, 5 by applying zinc fertilizer;6-11 by othertypes of agricultural interventions;12-14 by changes in processing or by acombination of interventions. Any nutrients that are increased throughagricultural means will need to be retained after processing to be of ben-efit for human nutrition, therefore the vigour of milling and structure ofthe grain are both important influences on the proportion of zinc lostthrough milling. Nutrients can get lost when the rice is cooked depend-ing on the amount of water used and whether or not it is discarded aftercooking. Ideally we should optimize the nutrient content at each stage tooffer many options to improve the nutrients available from rice. Whilstcontrolled experiments can show the theoretical zinc variability in rice,they do not show how variability occurs in field conditions. Combiningall these approaches in one study has not so far been undertaken (to ourknowledge) and is the subject of the research reported here.

Whilst the zinc content of rice is important, bioavailability influencesthe proportion of zinc absorbed. Consumption of foods other than ricenot only increases nutrient intake, but also affects bioavailability; it istherefore also important to consider the whole diet. The typical ruraldiet in Bangladesh consists of rice and sauce with small amounts of veg-etables and fish.15 Dietary factors likely to affect zinc bioavailability inthe Bangladesh diets are meat intake and phytate from rice.16 In Bangla-desh, the zinc:phytate molar ratio is estimated at 27.7 and just 3.1% en-ergy from animal sources implying low zinc absorption.2 Phytate isremoved from the outer layers of rice during milling so the balance ofimproved bioavailability and loss of zinc following milling is difficultto assess. Utilization of dietary zinc is also influenced by human condi-tions, such as diarrhoea that reduces uptake and intestinal infection.2 Di-arrhoea is part of a vicious cycle whereby absorption is decreased andpoor nutritional status results in susceptibility to diarrhoea.

In Bangladesh, rice is grown in three seasons: boro, the winter season(under irrigation), and two monsoon seasons (aman and aus). The rice isparboiled, a process involving soaking in warm water followed bysteaming and sun-drying on an earth floor. After parboiling, the rice ismilled to remove the husk. The polished rice is then boiled in water be-fore consumption.

The two objectives of the research were to assess (1) the variability inzinc content of rice in 4 villages in Bangladesh associated with the soil,rice variety, milling, and cooking, and (2) the contribution of variability

Original Research 21

in the zinc content of rice to zinc intake, bioavailable zinc, and zinc nu-tritional status of children.

METHODS

The study was a cross-sectional observational study of the usualpractice of growing, processing, and cooking rice with dietary and nu-tritional status assessments carried out on children in the rice producingcommunities. Figure 1 shows a schematic plan for the research. Fourvillages in different districts were selected for the study to obtain arange of soil types from the fourteen villages that formed part of the Na-tional Nutrition Survey of Bangladesh, organized through the Univer-sity of Dhaka.17 A random sample of 40 households was chosen fromthe census list in each village. The number of households was based onpractical considerations and the need to collect sufficient rice samplesfor differences in zinc content across villages. Each household had atleast 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 consentobtained. Ethical approval was obtained from the Cornell UniversityCommittee on Human Subjects and from University of Dhaka. Field-work was carried out in May and October-November 2000 before thestart of Ramadan, the Muslim month of fasting.

Both zinc and phosphorus contents were analysed for all the ricesamples collected. We were not able to analyze phytate, but have usedthe phosphorus content as an indicator for phytate content (see results).

1. Agricultural Production and Zinc and Phosphorus Contentof Un-Polished (Paddy) Rice

Soil and rice samples were collected from the boro and aman seasonsfrom four survey villages and surrounding areas; these additional siteswere sampled to obtain geographical variation in soils. The rice variet-ies collected provided genetic variability. During the harvest, farmerswere interviewed in their fields and identified the variety of rice. All therice was harvested from a 1m2 plot from the centre of each field, mixed,dried, winnowed, and weighed to assess yield. A sample of approxi-mately 50g rice was retained for chemical analysis. Soil inside the 1m2

harvest area was sampled using a soil auger to a depth of 15 cm. Tensamples were taken, mixed, then air dried, and a sample saved for analy-sis. The soil samples were analyzed for available zinc content and pH.


The number of soil and rice samples collected was driven by practicalconsiderations of time constraints rather than statistical considerationsbecause the magnitude of variability was not known in advance. It wasnot possible to obtain samples from the same farmer for both seasons.Multiple regression analysis was use to test the effects of soil availablezinc and pH on rice zinc content.

2. Changes in Zinc and Phosphorus After Milling

To measure impact of milling on zinc and phosphorus content ofrice, we collected 50g samples before and after milling from thestudy households and local mills in matched pairs of the same varietyof rice and the same household. Each time the rice was well mixedbefore taking the sample. The analysis is restricted to samples fromtwo villages where there was a local mill and hence sufficient sam-ples.

3. Changes in Zinc and Phosphorus After Cooking

Samples of polished rice before and after cooking matched byhousehold and variety were collected from the sample householdsduring the first visit in May. The samples collected at this time werepredominantly from the previous aman harvest. For this analysis weaimed for 20 samples from the survey households in each village.Some samples were spoiled and could not be analysed, therefore thefinal sample size was 73 from 4 villages. The person responsible forcooking in each household was asked about the source of water andwhether any water remained after cooking rice, and if so what wasdone with the water.


FIGURE 1. Schematic depiction of the passage of zinc from soil to humans

4. Village Differences in Zn and P Content of Polished Rice

A sample of polished rice was collected from each household at thetime of the dietary survey and the rice compositional analysis used to in-dividualize zinc intake from rice for each household. The respondentwas 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 in-terviewed during our second visit in October-November 2000. The 24-hour recall questionnaire format was provided by the International FoodPolicy Research Institute and previously field-tested. Trained enumera-tors conducted the interviews in Bangla. The respondent recalled all theraw ingredients of each dish (including rice) that were used to preparethe meals the previous day and the proportion of each cooked dish allo-cated to each household member. Adjustments were made for changesin weight of foods on cooking.18 Household measures were used for therecall, and then converted to gram equivalents. The dietary intake wasthen calculated for each household member in the household at the timeof the survey.

A nutrient composition database for foods other than rice was sup-plied by the International Centre for Diarrhoeal Disease Research, Ban-gladesh, and included zinc and energy content for Bangladeshi foods.19

The daily zinc intake was calculated using the individual rice zinc com-position data from each household and zinc intake from all other foodsusing food composition tables. The energy intake was calculated usingthe food composition tables. Daily intakes of food items for each familymember (including the 2-10 yr old child) were calculated using the in-gredients of each dish and household distribution.

The Estimated Average Requirements (EAR) for zinc as suggestedby the International Zinc Nutrition Consultative Group (IZiNCG) wereused to assess the adequacy of the diets.2 This recommendation repre-sents a mean requirement, or the dietary intake level at which 50% ofthe individuals would meet their physiological requirement. The levelfor unrefined, cereal-based diets was used based on the phytate:zincmolar ratio of 27.7 (2mg/d for 1-3 yr; 4mg/d for 4-8 yr; 7mg/d for 9-13yr). The individual dietary intakes of the children were comparedagainst the EAR within each age group.


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 indicatorof zinc status. A sample of hair was cut from behind the occipital boneof the children’s head close to the skull in lengths of 5 cm. For childrenwhose hair had recently been cut, shorter lengths were taken from awider area. Exogenous sources of zinc were removed before analysis bywashing in acetone. We were not able to collect serum samples due tothe practical constraints of transport, lack of electricity, and the consentrequired for an invasive procedure with no beneficial intervention.

Laboratory Analysis

Analyses for soil, rice and hair were carried out in the Soil and CropSciences Department at Cornell University, Ithaca, New York.

Rice Samples. Total mineral content (including zinc and phosphorus)was determined using an open acid digest.20 Approximately 25 g ofeach grain sample was dried and ground in a wiley mill. No particularprecautions were taken to determine the contamination from zinc. Asub-sample of 0.5g of the ground grain was digested with 1ml of con-centrated trace element grade nitric acid 69-70% concentration at1000C and an extra 1 ml of nitric acid was added three times approxi-mately every 2 hours and taken to dryness The heat was increased to1150C and nitric acid added another 2 times. One ml of 30 % hydrogenperoxide was then added. The solution was transferred to clean plasticcontainers and 25ml of 5% nitric acid added. In each batch of 100 sam-ples, a blank and a National Bureau of Standards (NBS) rice standardwas included. Duplicates were run for every 20 samples. The digestedrice solution was analyzed using an Inductively Coupled PlasmaAtomic Emission Spectrometer (ICP-AES) Spectro Ciros CCD. Thezinc and phosphorus content of grain was expressed as mg per 100g ofdry weight, a unit that is used in food composition tables. The coeffi-cient of variation was 4.0% Recovery of the minerals from the standardswas 102.5%.

Soil samples. The pH of the soil samples was determined in water us-ing a Fisher Accumet pH meter, model 620 standardized to pH 7 and pH4. Soil-available zinc was determined using DTPA extraction at pH 7.3.Twenty ml diethylene triamine pentaacetic acid (DTPA) was added to10 grams of air-dried soil at pH 7.3. The mixture was shaken at 120 cy-


cles per minute and 8cm stroke for 2 hours exactly. The extract was fil-tered through Number 42 Whitman’s filter into clean (acid washed)plastic containers. To preserve the samples, three drops of concentratednitric acid were added to each plastic bottle and samples were stored inthe refrigerator until analyzed. ICP-AES was used to determine the zinccontent of the extract. The results were adjusted for moisture content,which was calculated by drying a sample of soil for 2 days at 105°C andsubtracting this from the moist weight. Duplicate samples were run toassess the coefficient of variation, which was found to be 11.1% forzinc. Recovery was 99.8% using NBS standard. This extraction methodis commonly used for zinc, but will not necessarily reflect the field soilconditions because zinc availability changes under flooded conditions.For this reason the samples collected during the monsoon (aman) sea-son will not be as representative of soil available zinc as the samplescollected when the soil was drier during collection of boro samples.

Hair samples. Samples of approximately 0.1 g were washed withacetone and with three washes of distilled water then finally with acetone. 21

The same acid digestion procedure was used for hair as was used forrice samples. The samples were then analyzed using the ICP-AES. Thecoefficient of variation for 13 duplicate samples was 2.8%. A hair stan-dard was not used for the analysis.

Statistical Analysis. Data were analysed using SPSS22 for the major-ity of analyses. SAS23 was also used for calculation of daily nutrient in-takes. Student’s t test was used for the differences in the means of ricesamples. Pearson correlation coefficients were used for correlationanalyses. Anthropometric indices were calculated using Epi-Info 6.General linear models were used for analysis of association of multiplepredictors and an outcome variable.

RESULTS

Table 1 provides a summary of the samples collected.

1. Agricultural Production and Zinc and Phosphorus Contentof Un-Polished (Paddy) Rice

Over the two seasons of sample collection, farmers provided 39 vari-eties of rice. The varieties were different in the two seasons and fromdifferent regions (Table 2). It was therefore not possible to fully sepa-rate the effects of genetics and environment in the analysis and environ-mental conditions were different in the two seasons; hence the sampleswere analysed separately by season. Comparisons were made using just


the varieties for which we had more than 4 samples. The zinc content ofvarieties grown in the boro season varied from 1.57 to 2.16 mg/100g. Inthe aman season the zinc content ranged from 1.86 to 2.52 for differentvarieties. Overall the rice grown in the aman season had higher zinccontent than rice grown in the boro season (p < 0.001). The difference inP content was not significant. There was a strong positive correlationbetween zinc and phosphorus content (r = 0.50, p < 0.001).


TABLE 1. Summary of the Samples Collected

Yield was on average 441 ±149 g/m2 in the boro season and 220±107g/m2 in the aman season. Higher yield was associated with lowergrain zinc (r = -0.29, p < 0.001); this relationship was only significantwhen the two seasons were combined.

A regression model was constructed for the environmental influ-ences on the zinc content of rice including soil available zinc and pH.For the boro season, more acidic soils had higher grain zinc (p < 0.001)


TABLE 2. Grain Zinc (mg/100g) of Varieties of Un-Polished Rice Collected in TwoSeasons in Different Districts of Bangladesh. Only Those Varieties with Four orMore Samples Are Listed Here, Although All Samples Are Included in the Totals

and higher soil Zn was associated with higher grain zinc (p < 0.001) (R2

= 0.36). The relationship with soil Zn was on a log scale. For example, aten-fold increase in soil available zinc from 1ppm to 10ppm would re-sult in an increase of just 0.23 mg/100g in grain zinc.

Grain zinc (mg/100g) = 3.68-0.31 (pH) + 0.23 (log10 soil zinc)

This represents a large increment since the median soil available zincwas 1.1 ppm for the boro and 0.71 ppm for the aman season samples. Inthe aman season, the rice zinc was neither related to soil pH (p = 0.114)nor soil available zinc (p = 0.665).

2. Changes in Zinc and Phosphorus After Milling

More zinc was lost after milling in Batabaria (39%) compared toSimulia (24%) (p < 0.001). On the other hand, more phosphorus waslost in Simulia (39%) compared to Batabaria (25%) (p < 0.001) (Table3). It is not possible to separate the effect of village and rice varietysince different varieties were collected from the different villages.

3. Changes in Zinc and Phosphorus After Cooking

In Batabaria and Dhola, where pond water was used for cooking andthe excess discarded, on average 16% of zinc was lost on cooking. InSimulia and Padumhar there was little change in the zinc content andtube-well water was used for cooking and not discarded. Changes inphosphorus were also greater in Batabaria and Dhola than in Simuliaand Padumhar. Comparison between villages that use pond water and


TABLE 3. The Zinc and Phosphorus Content of Samples of Parboiled Unpol-ished Rice and Polished Rice Matched by Household and Variety Collected InTwo Villages During November 2000 Before and After Milling

tube-well water showed significant differences in the percentagechange in zinc and phosphorus on cooking (p < 0.01) (Table 4). Again,different varieties were available in the different villages making a com-parison of cooking methods and varieties impossible.

4. Village Differences in Zinc and Phosphorus Content of Polished Rice

Rice samples were home-grown (50%), obtained from the market(40%), or obtained from other local sources (10%). Village differencesin the percentage of home-grown rice were: 42% in Batabaria, 30% inDhola, 64% in Simulia, and 67% in Padumhar. Polished rice samplescollected from households in May (stored aman) on average contained1.26 ± 0.28 mg/100g zinc and in November (stored boro), 1.32 ±0.38mg/100g zinc with no significant difference between the two sea-sons. There were, however differences in the rice zinc content betweenvillages within season. Rice from Simulia had the highest zinc contentin the stored aman samples and Dhola had the highest zinc in the storedboro samples (Table 5). Phosphorus and zinc content of the polishedrice were highly associated (r = 0.66, p < 0.001).

Different varieties were generally available from different villages(Table 6). Both genetic and environmental differences could therefore


TABLE 4. The Zinc Content of Raw Polished Rice and Cooked Rice Matchedby Household and Variety Collected in Four Villages in May 2000 Before andAfter Cooking


TABLE 5. Average Zinc and Phosphorus Content of Polished Rice (mg/100g)in 4 Study Villages in 2 Seasons

TABLE 6. Zinc and Phosphorus Content of Polished Rice Samples Collected in4 Study Villages in Two Seasons. Only Those Varieties with Four or MoreSamples Are Listed Here, Although All Samples Are Included in the Totals

be important in determining the zinc content of the rice. Both rice vari-ety (p < 0.001) and village (p = 0.003) were significant predictors of ricezinc.

The usual phytate content of polished parboiled rice is 83mg /100g.19

The phosphorus we measured in polished rice was 158mg /100g. Froma crude calculation we approximate that phytate would account forabout half the phosphorus measured.

5. Dietary Intake of Zn Related to Zinc Content of Rice

The sample for dietary analysis from the 4 survey villages included194 children aged 5-10 yrs. They ate, on average, 378g rice per day. The83 children aged 2-4 consumed less rice, on average 258g per day. Theaverage contribution of rice to total intake was 66%.The high relianceon rice and the differences in the zinc content of rice affected the zincdensity of the overall diet in the different villages. The zinc density washighest in Dhola where the rice had the highest zinc content. The con-sumption of other foods with higher zinc density than rice was not suffi-cient to overcome the effect of rice zinc content on the zinc density ofthe overall diet in any of the villages. For example the high meat andfish intake in Batabaria was not sufficient to improve the zinc density ofthe diet in this village where low zinc rice was consumed (Table 7).

Most children (86.3%) were meeting the average daily requirementfor zinc by comparison to the EAR within each age group. The per-centage of children meeting the EAR for zinc in each village was dif-ferent (p = 0.10), with 79.5, 90.8, 84.6 and 92.2 for Batabaria, Dhola,Simulia, and Padumhar respectively. These differences relate not onlyto the zinc density of the diet but also total amount of food consumed.In Padumhar, the energy intake was higher than the other villages andthis compensated for the low zinc density of the diet; thus approxi-mately as many children were meeting their zinc requirements inPadumhar as in Dhola where the food intake was low but the zinc den-sity higher (Table 7).

6. Zinc Nutritional Status of Children Related to Zinc Content of Rice

A sub-sample of 191 children was able to provide hair samples (Table8). There were 86 (31%) children who did not provide hair samples be-cause they were either unavailable, had recently had their hair shaved orrefused to give a sample. The excluded children were more likely to befrom Batabaria (43%) and be aged 2-4 years (42%). Rice zinc and hair


zinc were positively associated (r = 0.24, p = 0.001). The association re-mained significant after controlling for age but was only apparent whensamples were pooled across villages. Other village-level differencescould therefore have also been important in this relationship. From thedata collected we identified the following possible other influences onhair zinc: age, amount of rice consumed, amount of meat and fish con-sumed (enhancers of bioavailability), and source of water. In a multipleregression model, higher hair zinc was associated with higher rice zinc(p = 0.018), increasing age (p = 0.038), lower fish and meat consump-tion (p = 0.013), and water source (p < 0.001), with unprotected river,pond, or canal water being associated with higher hair zinc than tube wellwater. Both fish and meat consumption and source of water were associ-ated in an unexpected direction. The amount of rice consumed was notsignificant in the model.


TABLE 7. Total Energy and Zinc in the Diets of Children Aged 2-10 with Contri-bution of Daily Zinc Intake from Rice and Zinc Density of the Diet

TABLE 8. Children’s Hair Zinc Content (ppm) in Each Study Village

DISCUSSION

Soil conditions were related to the zinc content of unpolished riceduring the boro season only. The relationship was, however, on a logscale implying that large increases in soil zinc would be necessary to in-crease grain zinc meaningfully. More acidic soils tended to have highergrain zinc, but this finding is of limited practical application because ofthe agronomic disadvantages of acid soils. During the aman season, the as-sociation of grain zinc with soil zinc and pH was not apparent. The wetconditions at the time of sampling could limit the validity of the methodchosen for assessing soil available zinc. Zinc tends to be more availablefrom acidic soils when they are dry than under flooded conditions whenthe pH increase. Another limitation was that soil was sampled from siteswhere rice was harvested, not from nursery plots where the youngplants were grown. This could limit the power to find a relationship ifthe early growing conditions affected zinc uptake. The relationship be-tween zinc in rice and available zinc in the soil is, however, potentiallyimportant and needs further investigation due to the dearth of studies onthis topic. When all samples were combined, grain zinc was negativelyassociated with yield, consistent with the “dilution effect” of increasingyield. This phenomenon presents a challenge when high yield and highnutrient content are both desirable.

It is possible to increase the zinc content of grain using zinc fertiliz-ers; for example, grain zinc increased by 63% 8, 42% 11, and 44% 9 withthe application of zinc fertilizers . Our results are consistent with thesefindings, but the applications of fertilizer would need to be high relativeto the zinc available in the sampled Bangladesh soils to increase the zinccontent by those magnitudes. There are also other ways to increasegrain zinc. For example, vesicular arbuscular mycorrhiza, a fungus thatfacilitates uptake of zinc by roots increased rice grain zinc by 32%.14

Organically grown rice was 10% higher in grain zinc than convention-ally grown rice.12 These and other strategies that could increase theamount or bioavailability of zinc have been previously reviewed. 24-27

In the future, a useful addition to a wide range of agronomic trials wouldbe analysis of grain and soil zinc that would help to determine whatpractices improve the zinc content of grain.

Different varieties of rice collected in different districts of Bangla-desh had very different zinc contents, both before and after milling.When varieties with at least 4 samples were compared, in the boro sea-son the variety with highest zinc in unpolished rice had 38% more zincthan the lowest variety. In the aman season, the variety with the highest


zinc had 36% more zinc than the lowest variety. Environmental vari-ability is also included in these differences since samples were collectedfrom different locations. The zinc contents of our samples are lowerthan some of the varieties identified by the International Rice ResearchInstitute; (wild rices and traditional or improved lines (3.79 and 2.42mg/100g respectively),4 but those samples were grown under experi-mental conditions and not under the often poor conditions of farmers’fields. There is much potential for improving grain zinc through plantbreeding, but good potential varieties need to be tested under farmers’field conditions. The zinc content of local varieties grown during theaman season compare favourably with the “BR” high yielding varietiesgrown in the boro season, but yields were on average only half of theyield in the boro season, so there appears to be a trade-off between grainzinc and yield.

The study design did not allow for a rigorous analysis of genetic andenvironmental interactions. There was a trade-off between rigorous de-sign, for example by the use of a controlled experiment of different vari-eties and soil types and the desire to collect “usual” samples fromfarmers. The advantage of our method is that it shows the magnitude ofimprovements that could be expected within the usual conditions inBangladesh farms.

The close correlation between zinc and phosphorus in both polishedand unpolished rice samples suggests that phytate content is likely to in-crease as zinc increases in grain. The implications for bioavailability areimportant. If phytate content rises in line with zinc, the benefit of extrazinc will be diminished. We have, however measured phosphorus, notphytate, so our conclusions are tentative. It is important in future tomeasure not only total phytate but to separate the different types ofphytate as their affect on bioavailability differs.28

Some clear differences in the effect of processing on grain zinc be-tween the villages were apparent. A controlled experiment would benecessary to determine whether the varieties or method of milling ex-plains the differences Laboratory experiments showed losses of zinc of36.4 ±14.2 % on average using a “McGill type miller no. 2” for 12 ricevarieties 29 and 34% average loss was reported.30 The loss of zinc fromour Bangladesh samples after milling of 39% from Batabaria is close tothese values and 24% lost in Simulia is less. The cooking of rice resultedin very different losses of zinc in different villages. In the villages wherepond water was used, then discarded, the cooking losses of both zincand phosphorus were greater than where tube-well water was used andnot discarded.


For various reasons, including genetic variability, agronomic prac-tice and processing, the zinc content of rice differed between the vil-lages to a degree that affected the zinc density of the whole diets in thesampled villages. If we had local composition data for all foods, wewould expect to find even greater local environmental influences on di-etary zinc intake. Zinc intake was on average highest in Dhola despitethis being the village with lowest energy intake and the lowest zinc frommeat and fish. This was because the rice had high zinc content at thetime of sample collection. This was also the village with the highest hairzinc content suggesting that the extra zinc supplied by higher zinc ricecould have improved zinc nutritional status. The zinc content of rice istherefore an important factor in total dietary intake and efforts toimprove it would be worthwhile to improve zinc nutritional status

There were few children who did not consume the EAR for zinc fromthe results of the 24-hour recall suggesting that for most children re-quirements should be met. With the high levels of infection, diarrhoea,and poor nutritional status of the children, however, their needs mayhave been higher than the EAR. For malnourished children, require-ments could be between 2-4mg/kg/d,2 much higher than the EAR. Us-ing this cut-off, nearly all the children would be below the recom-mended intake level. Given that nearly one-half of young children inBangladesh are stunted and underweight and about 12% are wasted 31 itappears that there is substantial risk of inadequate intake in the childrenin these Bangladesh villages. Efforts to improve zinc nutrition wouldtherefore likely result in health benefits for children.

The variability in the rice samples collected in the villages could notbe fully explained by the variability we have measured in the soil, in va-rieties chosen, milling losses, and cooking losses. The high zinc ricecollected in Dhola could have been caused by aspects of soil, varieties,or processing that we did not measure. The average zinc content of pol-ished rice in Dhola was highly influenced by the variety, boro aus thatwas grown in the aus season when we did not sample rice from fields.No other village grew rice during this season. Most of the other samplesof unpolished rice grown in Barisal district during boro and aman sea-sons did not have high zinc content, suggesting that the aus rice wasgrown under particular conditions or the varieties were different in theaus season.

How easy would it be for any one village to improve the zinc contentof its rice? The differences between the zinc content of the samplesshows the magnitude of difference that could be expected if differentpractices were employed or different varieties were chosen. Within a


village it is possible to switch from one variety of rice to another. Theapplication of zinc fertilizers or other agricultural interventions couldbe used. The process of milling could be adjusted to remove less zinc(although the bioavailability could change with more of the aleuronelayer left intact). More zinc could be retained if the water was not discardedafter cooking. The household rice samples were not all home-grown so thepower to influence the zinc content of rice through agricultural practicewould be limited to those who grow their own rice. Improvements inprocessing would, however, be accessible to all house-holds. Bioavail-able zinc could be increased most effectively by the addition of meat orfish to the diets of the children, and is recommended. However with thesevere poverty experienced in these communities, this option is beyondthe means of most households where we found very small quantities ofmeat and fish consumed by children.

The value of the research is that samples represent usual practicesand hence the options for change should be modest and within the graspof villagers. Further research on the constraints faced by villagers tochange their practices is also needed. In future, studies could includemore precise measures of bioavailability by measuring the phytate con-tent. Studies that separate the environmental and genetic components ofvariability would be useful. Similar research to determine factors influ-encing iron intake and iron nutritional status would also be valuable.The long-term aim of this work is to make recommendations to communi-ties for improving the nutrient content of their food through nutrient pre-serving and enhancing practices. It is important for villagers to be aware ofthese options and empowered to improve the nutrient content of their food.Various strategies to combat zinc deficiencies through food-based ap-proaches have already been described32 including dietary diversification,household production of foods and changes to processing. Our researchshows an example of the magnitude of change that one could expect toachieve through various improvements to the staple crop. The village-levelpractices suggested here could complement improvements in nutrientsachieved through conventional plant breeding and other strategies.

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Received: January, 2007Revised: June, 2007

Accepted: July, 2007

doi:10.1300/J477v02n01_03


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