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Supplement

Commentary on "Evidence That Iron Deficiency Anemia Causes Reduced Work Capacity"¹

Munk Centre for International Studies, University of Toronto, Toronto, Canada and the ^* International Food Policy Research Institute, Washington, DC.

²To whom correspondence should be addressed. E-mail: horton{at}chass.utoronto.ca.

	ABSTRACT

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 
This commentary assesses the strength of the causal evidence presented by Haas and Brownlie in this supplement and examines the potential magnitude of iron-deficiency anemia on welfare. From both the laboratory and field experiments, the evidence is strong and suggests that the potential magnitude of the effect of iron-deficiency anemia on work productivity is substantial. This commentary briefly discusses some of the limitations of using the estimates of effects on physiological capacity for measuring the effect on the social and economic well-being of individuals and society. Biological data are relevant to social and economic development, but additional field studies may be as important as the laboratory experiments to answer questions that also affect work productivity, household maintenance and child raising activities, and hence affect social and economic development. We extend the critical evidence review of human field studies that received disproportionately less attention than the laboratory studies in Haas and Brownlie. We provide some estimates of the magnitude of effects on well-being based on how this information has been used. Future field studies that examine the effect of iron-deficiency anemia and work output in an economic sense should measure increases in productivity but should complement this information with data on wages, income or some measure of profits to derive a money metric measure of increased productivity. Additional information on individual time allocation in household work, child care and leisure may also be required to capture social benefits deriving from improved work capacity.

KEY WORDS: • anemia • productivity • work

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 
Good evidence exists that anemia and iron deficiency cause reduced physical work capacity. Haas and Brownlie (2001) provide a very useful critical summary of the evidence, especially the laboratory evidence for humans and animals. Their review also provides briefer comments on field studies for humans. It explores different degrees of iron deficiency anemia (IDA)³ and iron deficiency without anemia (IDNA), and examines a wide range of laboratory (aerobic capacity, endurance, heart rate) and field study (aerobic capacity, endurance, heart rate, lactate, efficiency, economic return and voluntary activity) outcomes.

The main findings from their review are the following: 1) Diminished maximal physical working capacity (primarily measured by VO_2max) and decreased endurance result from IDA in humans. 2) The evidence is strongest that IDA causes reductions in aerobic work capacity (in both animal and human laboratory studies). 3) Field studies show that IDA impairs aerobic capacity. 4) Severe and moderate IDA (SIDA and MIDA, respectively) and IDNA also impair endurance, but most of the evidence comes from experimental animals. 5) Evidence from animal and human studies suggests a strong causal relationship between all levels of iron deficiency and voluntary physical activity (those studies are limited in numbers).

Some of the key contributions of their survey are the careful distinction between effects of iron deficiency and IDA; the careful distinction between effects via aerobic capacity (related to lower hemoglobin levels) and endurance or other factors affecting work ability such as energetic efficiency (which they relate to tissue oxidative capacity), hence, the link between IDNA and endurance or voluntary work activities and between IDA and aerobic capacity or maximum work capacity; and careful criteria to rate the laboratory studies on animals and humans.

Perhaps most useful, the authors assign causality ratings from a systematic evaluation of the studies, using well-defined criteria for internal validation, plausibility and external validation. Causality ratings were given for both the laboratory and field studies looking at the effect of anemia or IDA on economic outcomes. These were more useful for evaluating the laboratory studies because the more detailed summaries and a fuller discussion of these evaluations were unfortunately not available for the field studies. Fortunately, some of the literature that was reviewed by Haas and Brownlie has also been the foundation of previous work on the effect of IDA and economic consequences. We shall draw on these studies to discuss how this evidence has been used in the following sections.

The particular strengths of the paper are the contribution from the perspective of highly respected nutritionists focusing particularly on laboratory studies. Writing from the perspective of economists working usually with nonexperimental studies, we will therefore try to complement their review in the following six areas:

1. Identify ways the authors can distinguish between IDA and anemia not accompanied by iron deficiency and why this may have important policy implications; similarly, address why the authors may want to further explore the discussion of IDNA and human endurance.

2. Extend the critical evidence review of human field studies that receive disproportionately less attention than the laboratory studies in Haas and Brownlie, drawing on Ross and Horton (1998) .

3. Discuss the use and limitations of using the estimates of effects on physiological capacity for measuring the effect on the social and economic well-being of individuals and society.

4. Provide some estimates of the magnitude of effects on well-being based on how this information has been used to date.

5. Place the results on IDA within the broader context of the economic literature exploring the association between malnutrition and labor productivity.

6. Add some additional suggestions to Haas and Brownlie’s useful ideas for future research on the topic.

	Iron deficiency anemia, iron deficiency and anemia

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 
The Haas and Brownlie paper clearly distinguishes iron deficiency from IDA. Less time is spent on distinguishing IDA from anemia. It is more costly in the field to test for iron deficiency than for anemia. The former requires measurement of an indicator such as serum ferritin, which is more costly and expensive to do in the field, whereas anemia can be measured inexpensively using capillary blood samples. There is also less agreement on the best indicator of (and the appropriate cut-off value for) iron deficiency than there is for anemia.

We would like to encourage Haas and Brownlie to distinguish between IDA and anemia not associated with iron deficiency. This particular distinction is not clarified in the paper. The paper is at times even misleading; although the paper title states that the topic is iron deficiency and reduced work capacity, in practice in the field studies on human subjects, more than half of the studies examine simply the relation between anemia and work. Table 6 makes the appropriate split (anemia and IDA), but Tables 3 and 4 are misleading. Both of these tables refer to "Effect of SIDA, MIDA and ID"; however, according to Table 6, only 6 of the 13 studies in Tables 3 and 4 have measures of iron deficiency. Thus, what is being examined in the majority of cases is the effect of severe anemia, moderate anemia and iron deficiency, rather than SIDA and MIDA.

Do anemia unaccompanied by iron deficiency and IDA have different effects on function? As nonnutritionists, we do not know, but suspect that they do. If the cause of anemia is not iron deficiency but is related to underlying chronic conditions or infection, then these conditions or infections themselves are likely to have a separate effect on productivity. In some of the cases of an accompanying condition or infection, anemia is not accompanied by tissue iron deficiency, and the productivity effects are likely to be different from those of IDA. For policy purposes, one would also want to mention cases in which anemia is related to excessive iron loss (e.g., from parasite loads) rather than deficient intake. Some discussion of this issue would be useful. This is not to imply that all field studies have to measure iron deficiency as well as hemoglobin—which clearly would be difficult and expensive—but that it has to be clear whether anemia or IDA is being discussed, because the policy implications of the findings differ.

The Haas and Brownlie study does provide the very useful understanding that there are at least two separate mechanisms whereby iron deficiency can affect productivity. The first is via tissue oxidative capacity, which can affect endurance and efficiency, and is related to iron deficiency not necessarily accompanied by anemia. The second is via lower hemoglobin (anemia), which affects maximal work output. The paper effectively separates the different laboratory and field studies of iron deficiency and IDA. It also provides a very plausible explanation of why some studies in light physical work (where VO_2max is less likely to matter but where endurance does matter) have found such large productivity effects of iron deficiency on productivity.

However, we encourage the authors to push the analysis further, in particular, to the section on human laboratory studies, which is extremely brief and states "[T]he evidence strongly suggests that ID does not affect endurance capacity." However, this is at variance with several other pieces of the argument as follows:

Figure 1 (Haas and Brownlie 2001 ) implies that iron deficiency should affect endurance.

The animal studies imply that iron deficiency should affect endurance (3 studies).

The studies of voluntary activity for animals (1 study) and humans (1 study) also support a relationship with iron deficiency.

One of the four studies examined (Rowland, which scored 4 on the literature rating scale) supports the existence of a relationship between iron deficiency and endurance, although the other three (rated 3, 4, and 4 on the literature rating scale) do not. Of the three studies that do not, one has a sample size of only nine and the other two pertain to U.S. women (one study using healthy endurance runners); one would like to be more sure that the levels of iron deficiency observed in this U.S. population are similar to the levels observed in women in developing countries.

The authors state that using hemoglobin and serum ferritin levels "is not an accurate indicator of tissue iron status"; this could be a reason for the difference between animal and human studies. In animal studies (in which tissue iron deficiency can be more readily induced and measured), the relation was observed, whereas it was not in human studies. In the discussion section, the authors recommend using measures of tissue iron depletion such as the serum transferrin receptor in future studies.

In the light of this discussion, it is worth expressing the relationship between iron deficiency and endurance more cautiously and recommending further study of this issue. This is an important area for human welfare because IDNA may be a significant share of overall iron deficiency, and effects in light physical activity (related to endurance) may be quantitatively more significant than effects in heavy physical activity (related to maximal work output as well as endurance).

	Human field studies

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 
The Haas and Brownlie paper presents a comprehensive survey of the quality of the laboratory studies and provides a synthesis of the likely size of the effect on VO_2max. They conclude that IDA is associated with a 10–50% reduction in VO_2max. To extend this to implications for human well-being requires pushing the existing analysis further, both in the discussion of field studies and in giving quantitative estimates of the effect on work and productivity, not just physiological capacity. Obviously this requires the appropriate cautions because laboratory results are better controlled and more precise. The authors’ survey in the section entitled Literature Survey devotes half a dozen paragraphs to a discussion of 20 laboratory studies but only one paragraph to the 13 field studies. Extending the discussion of the field studies would be very helpful.

Ross and Horton (1998) surveyed some of the same field studies and evaluate 6 of the same 13. We clarified some of the issues surrounding interpretation of the results. It is much more difficult to fit field studies into an evaluative grid in the same manner as laboratory studies. Nevertheless, such an evaluation is necessary if it is desired to go further and to extrapolate the magnitude of the effects of anemia on measures of well-being. In some field studies, the study design meant that the likely effect on productivity was limited. For example, in the study of Li et al. (1994) , although workers were given incentives for higher productivity in terms of quality and quantity of yarn produced, the quantity was largely limited by the speed of the machine. Similarly in the study of Basta et al. (1979) , large productivity effects were observed in rubber tappers for whom output was readily measured and tied to pay but not in weeders for whom output was less readily measured. Similarly in the study of Edgerton et al. (1979) , workers did not have an incentive to pick more tea—in fact the opposite was true, because they would then have to carry out more tea.

	Use and limitations of estimates for measuring social and economic well-being

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 
The Haas and Brownlie paper reviews both laboratory and field studies. These can be used in different ways to extrapolate the likely effects on social and economic well-being. With respect to the laboratory studies, a serious question is how to use these findings on IDA and reduced capacity in an economic evaluation. For instance, Haas and Brownlie report that impairments are proportional to the severity of the deficiency and range roughly from 10 to 50% reductions in VO_2max. However, as economists, we wanted to know how this could be translated into a measure of change in increased work activity that could be used for an economic evaluation. For example, what would a 26% increase in VO_2max imply for work capacity?

Although the laboratory studies provide strong evidence of causality, the authors themselves warn that extrapolating from laboratory research to economic and social effects is not a direct process. They state explicitly that reductions in physical capacity do not translate into equal reductions in economic productivity. The conceptual framework presented in their Figure 1 helps to explain why laboratory research cannot capture all of the economic and social consequences. Primarily, other factors that affect productivity are not related to IDA and may not even be related to other health or nutritional deficiencies. This is an important issue and has been raised but not adequately addressed in previous research. Levin (1986) pointed out that a person’s capacity for work and actual output may differ for many reasons. Not all jobs draw on maximal aerobic capacities even though many of the jobs in developing countries do, at least for short periods. These include jobs in agriculture, industry, manufacturing, transport by foot and household chores such as collecting and transporting firewood and water and preparing foods (e.g., pounding cassava or yams or grinding grain). Although a person’s output will depend on intelligence, size, strength and build, incentives and motivation will also play a key role in work performance. Other factors may influence work output, such as weather conditions, alternative employment opportunities in places that have seasonal agricultural production, and availability and type of employment in sluggish economies, especially in urban areas.

However, we were still left wondering whether the physiological evidence could be used at all in an economic analysis. As mentioned, the physiological evidence from human laboratory trials is important for providing the evidence of the causal link and the plausibility of the relationship between IDA and work capacity, but in its current form it is unlikely that this evidence can actually be used in an economic evaluation. Although there might be a conversion factor to translate VO_2max to work capacity, the factor will depend on what task is being performed and how physically demanding it is. A single measure, such as aerobic capacity, will not capture the full effect on physical capacity because it omits the effect of IDA on endurance. Even using both aerobic capacity and endurance may not capture the effects of IDNA that might also affect work productivity through other mechanisms. In sum, such a conversion factor is difficult to identify and would be task specific (J. Ross, personal communication, 2000).

This explains why the existing studies exploring the effect of IDA on human welfare depend on the information provided from field studies. According to the causality ratings used by Haas and Brownlie, the economic studies range from 1 (weakest) to 4 (strongest), with the majority of the rated studies falling below 2.5. From the epidemiological criteria, economists appear to be using a set of studies that do not provide evidence on the causal relationship between IDA and work capacity that is as strong as evidence from laboratory studies. The lower ratings may indicate that the field studies have some limitations and could most likely be improved by using more appropriate evaluation designs and sampling methods. This has implications for increasing the number of field studies that examine this issue. It also points to the need for strengthening the methodological design for nonexperimental studies used to evaluate the effect of IDA on productivity.

	Effects on welfare

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 
Two major studies contribute to our knowledge on the social and economic consequences of IDA. The first study by Levin (1986) was a cost-benefit analysis of nutrition interventions for anemia reduction. To estimate the costs and benefits associated with supplementation and fortification programs, he had to estimate the effects of changes in hemoglobin on output. To do so, he reviewed eight studies of work output in relation to hemoglobin levels or changes in hemoglobin levels. From these studies he calculated an elasticity of work output with respect to increases in hemoglobin. An elasticity is simply the percentage change in work output given a percentage change in hemoglobin levels. He estimated that the elasticity is between 1 and 2, or that a rise in hemoglobin of 10% is associated with a rise in work output between 10 and 20%. Using this assumption, an increase in an individual’s hemoglobin of 20% and an elasticity of 1.5 suggests a rise in his output of >30%. Levin’s estimated elasticities were based on percentage changes found in the literature and not calculated directly by standard regression techniques. We are aware of only one study conducted by an economist that actually estimates an elasticity of work output with respect to an increase in hemoglobin levels.

Most of the field studies that examine the effect of IDA on economic output measure the changes in productivity as changes in the quantity of the commodity being plucked, picked, harvested or transported by the individuals in the study. However, to fully estimate the costs to society, these must be translated into a monetary value. Levin does this in his study and values the output in both social and economic terms. It is a long road to convert changes in the biological measure (change in hemoglobin status) to the measure of increased or reduced social and economic activity to an actual value of those changes. For instance, once the increase in output is established there is still the issue of assigning a monetary value to that change in output, which is not a straightforward task. Most labor used in rural agriculture comes from family labor. For hired labor, all kinds of formal and informal arrangements affect the going wage rate, ranging from reciprocity arrangements, in which no wages are exchanged, to hiring on a daily basis with a set daily rate and meal provision, to crop sharing, to wage setting by plantation and estate labor. The gender and age of the worker may also affect the wage. Women generally are paid less than men (often doing the same job) and children are paid less than women. Economists have methods for estimating wages for family and hired labor in these types of imperfect labor markets, but they require the use of detailed individual and household data (e.g., demographics, production, time allocation) and sophisticated econometric techniques. In Levin’s cost-benefit analysis, he uses estimates of average wages based on literature from the World Bank and the International Labor Office.

The same holds true for capturing the social benefits of additional output (i.e., the increase in home consumption of farm output for self-employed farmers) and other long-term benefits, such as lower morbidity and mortality, improved school performance, increased productivity at home, changes in time allocated to child care and other household activities or improved leisure time. Levin assumes that the social benefit of additional output is equal to half of the increase in earnings associated with greater productivity. For other long-term benefits, Levin assumes that total benefits of an intervention are 1.5 times the value of additional work in the labor market. We relay these somewhat detailed pieces of information to give the noneconomist a flavor of the types of benefits and costs that must be valued as well as the assumptions and analysis that go into estimating these costs.

Ross and Horton (1998) estimated the economic consequences of iron deficiency using a more global approach. They extrapolated from the field studies to try to make estimates of the order of magnitude of the effects of anemia. From the study of Li et al. (1994) , they assumed that anemia was associated with a 5% decrease in productivity in light manual work, and from the study of Basta et al. (1979) , a 17% decrease in heavy manual labor. They also assumed a 4% effect via cognitive ability (from other studies surveyed by Ross and Horton). Table 1 (from Ross and Horton) gives estimates for the costs involved for various countries. These costs are not insignificant. For south Asia, for example, the costs amount to $5 billion/y. The costs remain large even if the cognitive effects are omitted to be more comparable with the discussion in the Haas and Brownlie paper. Although the cognitive effects are very large (and tend to become more important in the richer countries), the effects in physical labor are still important (more than three fourths of a percentage of gross domestic product in Mali and as much as 1.5% in Bangladesh).

Extending the work by Haas and Brownlie may allow researchers to estimate the magnitude of the additional effects of IDNA. What would be useful is an estimate of the order of magnitude. One would also like to know about what proportion of anemia is related to iron deficiency (this likely varies by region, being higher in areas where malaria, human immunodeficiency virus, thalassemia and other chronic conditions are more prevalent). One would also like to have a rule of thumb, estimating how much IDNA is associated with a certain percentage of IDA. It would also be desirable to have estimates of the relative size of the effects on function of IDNA, IDA and anemia without iron deficiency.

	What can we learn from microeconomic studies exploring the association between malnutrition and labor productivity?

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 
Theories linking wages and productivity were developed as early as the 1950s and continued to be refined during the 1970s. However, before the mid-1980s, there were few empirical studies of the nutrition-productivity links in the field of household economics. A recent review of the economics literature on nutrition-productivity links indicates that there are strong associations between nutrition and labor productivity (M. Sur, unpublished data, 1999). Sur’s review of the literature covers economic studies that have looked at a number of different indicators of nutrition and labor productivity. A number of economic studies found that energy intake, height or weight for height (a measure for wasting) were significant predictors for wages and farm output (Deolalikar 1988 , Haddad and Bouis 1991 , Sahn and Alderman 1988 , Strauss 1986 , Thomas and Strauss 1997 ). Haddad and Bouis (1991) showed that an individual who was 15 cm taller than average was expected to earn 13% more. However, they did not find that energy intake was a significant predictor of wages. Only one study in Sur’s review used regression analysis to test the relationship between nutritional status and productivity, using hemoglobin as the measure for nutritional status (Wogemuth et al. 1982 ). The study found a weak but positive relationship between nutritional status and productivity. Sur’s review showed that although some of the evidence is contradictory, the general picture that emerged was that medium- and long-term nutritional status are important determinants of labor productivity, whereas short-term nutritional status, as measured by energy intake, is less conclusive.

Methodologically, studies that directly estimate the relationship between nutrition and productivity are different from the intervention studies that underlie the analyses carried out by Levin (1986) and Ross and Horton (1998) . They are microeconomic studies on the economic behavior of the individual or household and use primary data from detailed household surveys to estimate directly the relationship between nutrition and labor productivity by using regression analysis. Information is collected on individuals’ heights and weights, household expenditures, consumption, income, time allocation, assets and other types of social and demographic data.

Microeconomic analysis of individual and household behavior has the potential to shed additional light on the relationship between anemia or IDA and work capacity. Micro-level data from well-designed field studies should be better exploited. For example, IFPRI (1998) collected detailed information on individual and household characteristics (including time allocation data for women) and collected blood samples to measure hemoglobin levels for women and preschool children. The prevalence rates of anemia were high for adult women and preschoolers. The authors used regression analysis to observe variation in the levels of food intakes across individuals and seasons and measured the effect of diet on anemia. It would be useful to use such a data set to look at the relationship between hemoglobin levels and work output while controlling for other confounding factors. These types of studies would make an important contribution to strengthening the global estimates of the effect of anemia and IDA on work capacity specifically and overall well-being of individuals and society more broadly. However, to be comparable with the intervention studies, it would be necessary to ascertain the individual’s iron status.

	Summary and areas for future research

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 
The bulk of this paper is spent answering two main questions: What is the strength of the causal evidence that has been presented? What is the potential magnitude of the purported effect for the well-being of individuals and society? The evidence is strong and suggests that potential magnitude is substantial. Biological data are relevant to social and economic development, but additional field studies may be as important as the laboratory experiments to answer questions that also affect work productivity, household maintenance, and child-raising activities and hence social and economic development. Without additional information it is difficult to make full use of the biological data generated from laboratory studies.

Haas and Brownlie’s conclusions about the adequacy of these studies are that the evidence of the biological link between IDA and work capacity is sufficient and that further laboratory studies are not needed (J. Haas, personal communication, 2000). However, what is needed in developing countries is a test of the causal relationship of anemia to performance with levels of exertion and types of tasks found in rural and urban areas of developing countries.

Haas and Brownlie suggest four useful directions for future research: 1) laboratory studies with humans, verifying tissue iron status, for example, with the serum transferrin receptor; 2) more studies of the effect of anemia on voluntary physical activity and standardizing assessment tools to be able to do this; 3) incorporating the issue of motivation in field studies of anemia and productivity; and 4) extending the analysis of the effect of anemia into nonmarket work activity, such as child care, household maintenance, and social and leisure activities.

These are useful suggestions. The first issue (tissue iron status) is something that it would be useful to establish in laboratory studies. As mentioned above, we do not have a good idea of the relative magnitude of the productivity loss associated with IDA, anemia (in the absence of iron deficiency) and IDNA. Because measuring these separately in field situations is likely to be impractical in most cases, some guidance from closely controlled field studies would be very useful. It would be particularly useful to obtain an understanding of the relative size of effects on function of IDNA, IDA and anemia without iron deficiency. In addition to laboratory results on function, prevalence data on the relative prevalence of IDNA, IDA, and anemia without iron deficiency would also be useful.

The third issue (motivation) was discussed briefly above. Clearly, it is very important to evaluate motivation in the existing field studies and to examine it carefully in new human field studies. The literature on energy supplementation also confirms that it is very important (offering cigarettes in some of the early energy supplementation experiments proved as strong an inducement as more food for increasing output).

The second and fourth issues are related. Here the field studies of the effects of energy supplementation may be useful because there are more of these than iron supplementation studies. Some of the existing energy studies (e.g., those by Instituto de Nutrición de Centro América y Panamá) have looked at effects on voluntary activity, and existing survey instruments could be useful for iron supplementation studies. The effects on voluntary activity (nonmarket activity) are likely to be quite large and important for an individual’s well-being. The brief survey in Ross and Horton (1998) suggests that the effects of IDA on child care and cognitive development are likely to be large and economically important. Developing countries are shifting to more white-collar work, globalization implies more rapid changes in work environments, and adaptation to change and ability to acquire new skills are increasingly important. The cognitive area (in which both anemia of the child and of the mother matter) is likely to be a promising area for additional work.

Evaluating the economic effect of iron deficiency and IDA on voluntary physical activity and nonmarket activities is a challenging task. Therefore, further work in this area (issues 2–4) would have to be linked to detailed household surveys including information on the time allocation of individuals at the household level by using several outcome indicators related to both aerobic capacity and endurance. As discussed earlier, it might be necessary to measure iron status as well as anemia.

In addition, future field studies that examine the effect of IDA and work output in an economic sense should measure increases in productivity but should complement this information with data on wages, income or some measure of profits to derive a money metric measure of increased productivity. Additional information on individual time allocation in household work, child care and leisure may also be required to capture social benefits deriving from improved work capacity.

How to carry out these studies may be as important as determining what additional studies are warranted. For example, future research should be designed and carried out by multidisciplinary teams comprising both economists and nutritionists. In addition, field studies must be more methodologically rigorous. Randomized evaluation design or quasi-experimental design can and should be used to assess the relationship between IDA and work capacity by using a wide range of outcome indicators. Quasi-experimental design should strengthen the causal evidence because it can assess the effects of a given intervention by measuring the social and economic changes of the target group and systematically isolating the effects of other factors (Valadez and Bamberger 1994 ).

	FOOTNOTES

 
¹ Presented at the Belmont Meeting on Iron Deficiency Anemia: Reexamining the Nature and Magnitude of the Public Health Problem, held May 21–24, 2000 in Belmont, MD. The proceedings of this conference are published as a supplement to The Journal of Nutrition. Supplement guest editors were John Beard, The Pennsylvania State University, University Park, PA and Rebecca Stoltzfus, Johns Hopkins School of Public Health, Baltimore, MD.

³ Abbreviations: IDA, iron-deficiency anemia; IDNA, iron deficiency without anemia; MIDA, moderate iron-deficiency anemia; SIDA, severe iron-deficiency anemia.

	REFERENCES

TOP ABSTRACT INTRODUCTION Iron deficiency anemia, iron... Human field studies Use and limitations of... Effects on welfare What can we learn... Summary and areas for... REFERENCES

 

1. Basta S., Soekirman S., Karyadi D., Scrimshaw N. S. Iron deficiency anemia and the productivity of adult males in Indonesia. Am. J. Clin. Nutr. 1979;32:916-925[Free Full Text]

2. Deolalikar A. B. Nutrition and labor productivity in agriculture: estimates from rural south India. Rev. Econ. Stat. 1988;70:406-413

3. Edgerton V. R., Gardner G. W., Ohira Y., Gunawardena K. A., Senewiratne B. Iron-deficiency anaemia and its effect on worker productivity and activity patterns. Br. Med. J. 1979;2:1546-1549

4. Haas J., Brownlie T. Iron deficiency and reduced work capacity: a critical review of the research to determine a causal relationship. J. Nutr. 2001;131:676S-690S[Abstract/Free Full Text]

5. Haddad L., J & Bouis H. E. The impact of nutritional status on agricultural productivity: wage evidence from the Philippines. Oxf. Bull. Econ. Stat. 1991;53:45-68

6. IFPRI Bangladesh, Institute of Development Studies, Institute of Nutrition and Food Science, Data Analysis and Technical Assistance Research Department of Human Nutrition, Royal Veterinary and Agricultural University Commercial Vegetable and Polyculture Fish Production in Bangladesh: Their Impacts on Income, Household Resource Allocation, and Nutrition, Report, Vol. 1 1998

7. Li R., Chen X., Yan H., Deurenberg P., Garby L., Hautvast J. G. Functional consequences of iron supplementation in iron-deficient female cotton mill workers in Beijing, China. Am. J. Clin. Nutr. 1994;59:908-913[Abstract/Free Full Text]

8. Levin H. A benefit-cost analysis of nutritional programs for anemia reduction. World Bank Res. Observer 1986;1:219-246[Abstract/Free Full Text]

9. Ross J., Horton S. Economic Consequences of Iron Deficiency 1998 Micronutrient Initiative Ottawa, Canada.

10. Sahn D. E., Alderman H. The effects of human capital on wages and the determinants of labor supply in a developing country. J. Dev. Econ. 1988;29:157-183

11. Strauss J. Does better nutrition raise farm productivity?. J. Polit. Econ. 1986;94:297-320

12. Thomas D., Strauss J. Health and wages: evidence on men and women in urban Brazil. J. Econometr. 1997;77:159-185

13. Valadez J., Bamberger M. Monitoring and Evaluating Social Programs in Developing Countries: A Handbook for Policymakers, Managers, and Researchers 1994 EDI Development Studies. The World Bank Washington DC.

14. Wolgemuth, J. C., Latham, M. C. & Chesher, A. (1992) Worker productivity and the nutritional status of Kenyan road construction laborers. Am. J. Clin. Nutr. 36: 68–78. 360.

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