Iron Nutrition Does Not Account for the Hemoglobin Differences between Blacks and Whites

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1 Human and Clinical Nutritin Irn Nutritin Des Nt Accunt fr the Hemglbin Differences between Blacks and Whites GERALDINE S. PERRY, ' TIM BYERS, RAY YIP AND SHELDON MARGEN* Epidemilgy Branch, Divisin f Nutritin, Natinal Center fr Chrnic Disease Preventin and Health Prmtin, Centers fr Disease Cntrl, Atlanta, GA and *Nutritin Prgram, Schl f Public Health, University f Califrnia, Berkeley, CA ABSTRACT Many researchers have reprted lwer he mglbin cncentratins in blacks than in whites, but the reasn fr this difference is unknwn. Data fr 2515 persns (in 3-12 y and y age grups) frm the Secnd Natinal Health and Nutritin Examinatin Survey (NHANES II) were evaluated t investigate the rles f irn intake and bichemical irn status indi catrs in explaining black and white differences in hem glbin cncentratin. Dietary irn intake was estimated frm ne 24-h fd recall, and hemglbin, serum fer ritin, transfert-in saturatin and erythrcyte prtprphyrin were measured by standard labratry methds. Hemglbin levels were substantially lwer in black children (120.3 g/l) than in white children (126.8 g/l). Hemglbin cncentratins were als lwer in black wmen (128.4 g/l) than in white wmen (133.9 g/l), and in black men (144.8 g/l) than in white men (153.2 g/l). Blacks had lwer hemglbin cncentratin than whites at mst levels f dietary irn intake, serum fer ritin, transferrin saturatin and erythrcyte prtprphyrin. Despite their lwer hemglbin levels, blacks had higher serum ferritin levels than whites. These results suggest that the difference in hemglbin cncentra tins between blacks and whites in the United States is the result f factrs ther than irn intake and irn status. Mre specific investigatins f bth the genetic and envirnmental determinants f irn utilizatin in blacks are needed. J. Nutr. 122: , INDEXING KEY WORDS: â /Y/-//\/YES// â hemglbin â race â irn deficiency â serum ferritin As early as the 1930s, investigatrs were able t demnstrate an unexplained difference in the hem glbin cncentratin f blacks and whites (Eads et al. 1949, Milam et al. 1946, Munday et al. 1938). Mre recently, using data frm U.S. natinal surveys, inves tigatrs (Dallman et al. 1984, Garn et al. 1975, 1976, 1977, 1980, 1981, Jhnsn et al. 1979, Meyers et al. 1979, 1983, Owen et al. 1973, 1977, Yip et al. 1984) have generally shwn blacks t have hemglbin levels that are g/l lwer than whites. These differences are greater than thse that have been fund by researchers using data frm studies that were nt natinal surveys ( g/l) (Caramihai et al. 1975, Dallman et al. 1978, Frerichs et al. 1977, Jacksn et al. 1983, Kraemer et al. 1975, Reeves et al. 1981, Williams et al. 1981). Differences have persisted even after cntrlling fr age, incme, dietary irn intake and transferrin saturatin. Sme have at tributed the lwer hemglbin levels in blacks t genetic differences (Garn et al. 1975, 1976, 1977, 1980, 1981, Owen et al. 1977), althugh n specific genetic studies have been cnducted t answer this questin. Mst investigatrs have adjusted fr nly ne ptential cnfunding factr at a time, and few have used a multivariate apprach. Even fewer re searchers have studied black-white differences in he mglbin cncentratins while taking irn intake and irn nutritin status int accunt (Jacksn et al. 1983, Williams et al. 1981). The Secnd Natinal Health and Nutritin Exami natin Survey (NHANES II) prvided the first available data set with cmplete infrmatin n the prper variables needed fr assessment f irn status fr a large ppulatin sample. Additinally, NHANES II cllected hemglbin electrphresis data, thereby making it pssible t exclude persns with hemglbinpathies that culd affect the hemglbin cncentratin. This data set als allws fr the cntrl f a number f ther ptential cnfunding factrs thrugh multivariate analysis. The purpse f this study was t further explre the pssible reasns fr lwer hemglbin cncentratins in blacks by "T whm crrespndence and reprint requests shuld be ad dressed /92 $3.00 Â 1992 American Institute f Nutritin. Received 27 September Accepted 28 February

2 1418 PERRY ET AL. examining race differences in hemglbin as related t irn intake and bld markers f irn transprt, utilizatin and strage. SUBJECTS AND METHODS NHANES II sample. The present study is based n the analysis f data frm NHANES II. In NHANES II, data were cllected n 27,803 civilian nninstitutinalized persns, ages 6 m t 74 y, between February 1976 and February 1980, thrugh multistage stratified randm cluster sampling, using an apprved prtcl fr the study f human subjects. Cmplete hã mat lgie and bichemical data (including serum ferritin values) were cllected n a subset f 5157 persns. A detailed explanatin f the NHANES II data cl lectin methds has been previusly published (Na tinal Center fr Health Statistics 1981). Study sample. Only bservatins with serum fer ritin determinatins were used in the present study. We excluded frm this analysis all persns wh were <3 y, >12 and <18 y, r >45 y f age (n = 2373), pregnant (n = 72), nt black r white (n = 71), had a serum ferritin value >300 ug/l (n = 29) r a hem glbin phentype ther than AA (n = 97). Children ages >12 y and <18 y were excluded frm these analyses because f the difficulty t cntrl fr rapidly changing physilgic status related t grwth and sexual maturatin during this perid. Persns >45 y were excluded because f their increased prbability f chrnic inflammatry diseases r ther health cn ditins that can decrease hemglbin and increase serum ferritin levels. Certain hemglbinpathies can als lwer hemglbin cncentratin. Therefre, persns with hemglbinpathies were excluded frm the study, althugh the difference in hemglbin be tween blacks and whites was nly 0.2 g/l greater when persns with abnrmal hemglbin were in cluded cluded in the analysis. The a ttal f 2515 persns final study sample in ages 3-12 y r y. HÃ matlgie and irn bichemistry variables. The hã matlgie variables were determined using bld cllected by venipuncture. Hemglbin was deter mined using Culter hemglbinmeter (Culter Electrnics, Hialeah, FL). Serum ferritin was mea sured by RIA using the tw-site immunradimetric methd (Miles et al. 1974). Serum irn and ttal irnbinding capacity were determined by a mdificatin f the Autmated Technician AA11-25 methd, based n prcedures f Givanniell et al. (1968) and Ramsey (1957). Transferrin saturatin as the rati f serum irn (uml/l) was expressed t ttal irnbinding capacity (uml/l), multiplied by 100. Erythrcyte prtprphyrin levels were determined by using a mdificatin f the methd f Sassa et al. (1973). Hemglbin phentypes were determined by prtein electrphresis. Detailed infrmatin n the labratry methds used in NHANES II has been previusly published (Gunter et al. 1981). In the present study irn deficiency was defined as a serum ferritin <12 ug/l, a transferrin saturatin <16% r an erythrcyte prtprphyrin level >1.42 uml/l f RBC. Dietary infrmatin. Dietary irn intake mated frm a single 24-h fd recall. Irn was esti intake is reprted as the ttal irn (milligrams per day) frm all dietary surces, excluding supplements. Statistical analysis. The gender fr adults ages data were y because stratified by f differences in irn nutritin related t menstrual and repr ductive children factrs, but they ages 3-12 y because were nt stratified fr there are n hemglbin differences between sexes in childhd. When the number f men in any given stratum was <10, they were excluded frm the analysis. Thus men were excluded frm the analysis f hemglbin by cate gries f irn status indicatrs and dietary irn in take. Fr the same reasn, men and children were excluded frm the analysis f the prevalence f anemia by irn status. Serum ferritin and transferrin saturatin values were transfrmed t their natural lgarithm t achieve and thereby imprve a mre Gaussian distributin the statistical pwer. The antilg f the values was then expressed as gemetric means f ferritin and transferrin saturatin. Standard errrs fr the lg-transfrmed variables are nt pre sented in the tables because they are meaningless. Hypthesis testing was perfrmed using the lg-trans frmed means and SE f serum ferritin and transferrin saturatin. Mean differences were cnsidered statisti cally significant at P < The SE f all the means were calculated by using the Sesudaan prgram (Shah et al. 1980) t accunt fr the sample weight and the cmplex sampling strategy used in NHANES II. All means given in the tables have been adjusted fr age. The cntributin f the study variables t the vari atin in racial hemglbin cncentratins and statis tical significance f the differences f hemglbin levels between blacks and whites were assessed using analysis f cvariance under the General Linear Mdel prcedure f SAS, versin 5 (SAS Institute, Cary, NC). RESULTS Crude differences in mean hemglbin cncen tratin were evident in all age grups (Fig. 1) and were greater in males at each age. Althugh the race dif ference in hemglbin was similar in children (6.5 g/ L) and wmen (5.5 g/l), it was much greater in men (8.4 g/l) (Table 1). Fr bth children and men, the dietary irn intake was cmparable between blacks and whites (Table 2). Black wmen had a smewhat lwer intake f dietary

3 HEMOGLOBIN DIFFERENCES BETWEEN BLACKS AND WHITES BlackFemales TABLE 1 Age-adjusted hemglbin fr U.S. adults and children, by age and race: NHANES II1 4* CO C Q> e O e 2 "ñ -2 E z D Black Males White Males 3-1 O Age (years) FIGURE 1 Hemglbin cncentratin by age fr blacks and whites, ages 3-12 y and y: NHANES II, irn than white wmen but the difference was nt statistically significant. Overall, black men had similar irn status t white men, as indicated by serum ferritin, transferrin saturatin and erythrcyte prtprphyrin (Table 2). Black wmen seemed t have better irn status than white wmen, as indi- Sex (age), race Men (18^15 y) Black White Race difference2 Wmen (18^5 y) Black White Race difference2 Children (3-12 y) Black White Race difference Hemglbin (1.2) (0.3) (0.9) (0.4 (0.7) (0.3) 6.5 Values are means with SE in parentheses, age-adjusted by analysis f cvariance. 2P < cated by higher serum ferritin levels and lwer eryth rcyte prtprphyrin. Hwever, black children seemed t have prer irn status than white chil dren, as indicated by lwer transferrin saturatin and higher erythrcyte prtprphyrin levels. The mean hemglbin cncentratins fr wmen and children at varius levels f dietary irn intake, serum ferritin, transferrin saturatin and erythrcyte prtprphyrin are displayed in Table 3. The mean TABLE 2 Age-adjusted dietary irn intake, serum ferritin, transferrin saturatin and erythrcyte prtprphyrin level fr adults and children, by age and race: NHANES II1 Sex (age), racemen irnmg/d16.18 ferritin2w/l ** l* **transferrin saturatin2% ** ** prtprphyrinymlll1.34 y)blackwhiterace (18-45 differencewmen y)blackwhiterace (18-45 differencechildren y)blackwhiterace (3-12 differencen dietary (1.48)16.91 (0.58)0.73**9.84 (0.71)11.27 (0.49)1.43**11.83 (0.86)11.63  0.32)-0.2* *Serum 'Values are means with SE in parentheses. *P < **Nt statistically significant (P ^Standard errrs are nt given fr gemetric means. 0.05). ""P (0.55)1.32 (0.35)-0.02**0.93 (0.04)1.28 (0.17)0.35***1.25 (0.20)1.13 (0.14)-0.12*

4 1420 PERRY ET AL. LU Z LL O 111 u LU OC D D Black White 0123 NUMBER OF POSITIVE IRON DEFICIENCY TESTS FIGURE 2 The prevalence f anemia (hemglbin <120 g/l) in black and white wmen when irn deficiency is indicated by zer, ne, tw r three psitive irn deficiency tests (ferritin <12 p.g/l, transferrin saturatin <16% r erythrcyte prtprphyrin >1.42 iml/l). hemglbin cncentratin fr black children was sig nificantly lwer than fr white children at all dietary irn intake levels, except thse >15 mg/d. The mag nitude f the race difference decreased in children as irn intake increased, whereas in wmen, the race difference was smallest (2.1 g/l) when daily irn intake was inadequate (<10 mg/d). Blacks had lwer hemglbin levels than did whites at all levels f TABLE 3 serum ferritin. Hwever, the difference was nt statis tically significant when irn stres were inadequate (ferritin levels <12 (ig/l). The greatest race difference in children (11.8 g/l) was bserved when serum fer ritin levels were highest ( ug/l), whereas the greatest difference in wmen (7.9 g/l) ccurred when ferritin levels were marginal (12-30 ug/l). Lwer he mglbin cncentratins were als bserved in blacks at all levels f transferrin saturatin, thugh the dif ferences were nt statistically significant at higher levels f transferrin saturatin in wmen. Blacks had lwer hemglbin cncentratins than whites at all levels f erythrcyte prtprphyrin, except at levels >1.42 nml/l in wmen, where the sample size was very small. Figure 2 cmpares the prevalence f anemia in black and white wmen accrding t the number f psitive irn deficiency tests. Overall there was a strng trend f increasing prevalence f anemia with an increase in the number f psitive irn deficiency tests. At each level f irn status, black wmen had a higher prevalence f anemia and lwer hemglbin levels than white wmen (the race differences were 5.9, 6.0, 5.6 and 5.1 g/l when the number f psitive irn deficiency tests were 0, 1, 2 and 3, respectively). Hwever, the hemglbin differences were smaller and nt statistically significant when irn deficiency was indicated by tw r three psitive tests. Mst imprtantly, 28% f black wmen had a hemglbin Age-adjusted hemglbin cncentratin by irn intake, ferritin level, transferrin saturatin and erythrcyte prtprphyrin level fr children ages 3-12 y and wmen ages y1 ChildrenIrn difference2.1**11.8*8.52>*ferritin intake,< >15blackmg/d121.1 (1.2)124.9 (1.3)129.4 (1.4)126.1 (0.4)129.7 (2.8)n883732White128.3(0.8)n Race \ig/l< transferrin< >30erythrcyte> < level, (0.7)122.9 (1.5)129.7 (1.3)118.6 (0.9)130.4 (1.1)saturatin, (0.5)126.5 difference7.2*4.5*3.6**wmenblack (1.6)(2.5)(1.7)n833621white133.0 (1.9)135.0 (0.7)134.1 (1.1)n Race (1.8)135.3 (1.3)135.4 (0.9)132.0 %120.6 (0.4)123.5 (2.0)126.5 (1.4)129.2 (0.7)131.4 (0.8)133.9 (0.7)135.2 (0.8)prtprphyrin115.6 (1.1) **7.9*6.3*7.4*6.3*2.1**level, (0.8) **6.7*11.8*5.9*5.7*4.82'* (2.2)(2.0)(1.5)(1.2)(1.9)(2.1)392 imi/i (2.2)123.0 (1.5)122.9 (1.3)127.6 (1.6)129.9 (2.0)132.6 (0.6)135.5 (1.3) (0.7) '*4.6*7.0* (6.7)(2.0)(1.8) (0.7) '**5.72'*6.3* 'Values are means with SEin parentheses. Men were excluded frm these analyses due t small numbers in strata f dietary irn intake <10 mg/d, ferritin <12 lig/l, transferrin saturatin <16%, and erythrcyte prtprphyrin >1.42 uml/l. 'P < "Nt statistically significant. 2May be unreliable due t small numbers.

5 HEMOGLOBIN DIFFERENCES BETWEEN BLACKS AND WHITES 1421 TABLE 4 Adjusted race differences in hemglbin cncentratin and r fr children 3-12 y, and adults 1&-45 y: HANES II1 Children2 Men Wmen Adjustment factrsunadjustedageage, differenceg/l6.7*6,5*6.4*6.3*6.3*6.3*r race differenceg/l8.2*8.4*8.4*8.4*8.5*8.5*â Race differenceg/l6.0*5.5*5.5*5.3*5.5*5.5*r20. irnage, %Age, irn, TS,3 TS,3%, irn, ferritin3age, TS,3%, irn, ferritin, incmerace 'n = 620 white children, 140 black children, 646 white men, 101 black men, 767 white wmen and 140 black wmen fr each mdel, r2 = crrelatin cefficient, amunt f variatin in black and white hemglbin difference explained by the variables in the mdel. 'P < Values presented fr children are sex-adjusted. 3Natural lgarithm f transferrin saturatin (%) and ferritin used. TS - transferrin saturatin, irn is ttal dietary irn intake. cncentratin <120 g/l (a value cmmnly used t define anemia), even when irn deficiency was nt present (n psitive irn deficiency tests). Hemglbin cncentratin differences between blacks and whites established after step-wise multivariate adjustment fr age, incme, parity, dietary irn intake, transferrin saturatin and serum ferritin are presented in Table 4. Step-wise adjustment fr these cvariates shwed that althugh these variables are cmmnly thught t be sme f the mst im prtant surces f variatin in hemglbin levels in healthy individuals, they were nt imprtant cntrib utrs t the differences in hemglbin cncentratins between blacks and whites in this study. It shuld be nted that the full mdel explained nly a small percentage f the ttal variatin in hemglbin differ ences between blacks and whites: 25.4% fr children, 12.3% fr wmen (includes parity, mdel nt shwn in table) and nly 6.3% fr men. DISCUSSION This study cnfirmed that blacks have lwer hem glbin levels than whites even after cntrlling fr ptential cnfunding factrs f age, sex, dietary irn, serum ferritin, transferrin saturatin, incme and parity. Table 5 prvides a cmparisn f ur findings with thse frm previus studies. The adjusted mean racial difference f 6.3 g/l fund in children in this study was greater than thse previusly reprted by Owen et al. (1973, 1977), Reeves et al. (1981), Dallman et al. (1978) and Caramihai et al. (1975), was similar t that fund by Dallman et al. (1984) in anther study, but smaller than the findings reprted by Frerichs et al. (1977). The race difference f 8.4 g/l bserved in men was much greater than the 2.7 g/l difference fund by Jacksn et al. (1983) and the 5.0 g/ L difference fund by Kraemer et al. (1975), similar t thse fund by Dallman et al. (1984) but smaller than the difference reprted by Garn et al. (1975) and Wil liams (1981). The adjusted mean racial difference f 5.3 g/l fund in wmen was greater than the 4.8 g/l fund by Williams (1981) but smaller than the 8.0 g/l reprted by Dallman et al. (1984), and Meyers et al. (1979), and the 9.9 g/l difference reprted by Garn et al. (1975). Dallman's findings f higher hemglbin difference in wmen, using data frm the same NHANES II data set, are likely the result f methds f analysis and different selectin criteria fr in clusin in the sample. The findings reprted here exclude thse with a ferritin level >300 ug/l, were adjusted fr age within the brad categries f age and are reprted as mean (nt median) values. Althugh black men, wmen and children had lwer mean hemglbin cncentratins and lwer di etary irn intakes than did whites, their mean serum ferritin cncentratins (irn stres) were greater. Higher serum ferritin cncentratins have been re prted previusly in black men by Jacksn et al. (1983) and Williams (1981), and als in black wmen by Williams (1981). Bazzane et al. (1986) have als reprted higher ferritin cncentratins in black chil dren. Lwer hemglbin levels but higher serum fer ritin levels in blacks culd indicate that blacks have reduced mbilizatin f irn frm stres fr hem glbin synthesis. One pssible limitatin f this study is that irn intake was measured by a single 24-h dietary recall. This assessment tl has been shwn t give a repre sentative estimate f grup daily intake, althugh it is nt as accurate as ther tls in estimating dietary intake f individuals. Hwever, because this study investigates grup differences, this dietary intake tl

6 1422 PERRY ET AL. is likely nt a majr limitatin. Higher serum ferritin cncentratins seen in blacks culd be due t greater irn intake, if the dietary irn intakes reprted by blacks were an underestimatin f their true dietary intake. Additinally, the cmpsitin f the diet culd cause decreased irn absrptin, but this des nt seem t play a majr rle in explaining the differ ences in hemglbin fund here because the bdy irn stres in blacks, indicated by ferritin levels, are equal r higher than thse in whites. Because acute infectins r chrnic inflammatry diseases such as arthritis can cause decreased hem glbin and irn-binding capacity while causing elevated serum ferritin cncentratins (Yip et al. 1988), the higher serum ferritin levels in blacks b served in this study culd result frm a higher preva lence f acute infectins and chrnic inflammatry diseases. Hwever, the latter explanatin is less likely, because lder persns (>45 y) wh were mst likely t have sme type f chrnic inflammatry disease were excluded frm these analyses. Anther pssible explanatin fr the lwer hemglbin levels bserved in blacks is that, althugh persns with certain hemglbinpathies were excluded frm the analysis, it is pssible that blacks may be mre likely t have hemglbinpathies such as a and ß thalassemia trait, hemglbin C trait, hemglbin S trait, r hemglbin S/C trait that are t mild t be detected by the hemglbin electrphresis methds used in the detectin f abnrmal hemglbin (Jhnsn et al. 1982, Pierce et al. 1977). The lwer transiern saturatin and higher erythrcyte prtprphyrin levels in black children may indicate a higher prevalence f irn deficiency in black children than in white children, althugh this is nt reflected in serum ferritin levels. Bazzane et al. TABLE 5 Summary f hemglbin differences between blacks and whites fund in selected previus studies and in the current study1'2 Surce differenceg/lchildrenowen f dataagegenderraceblackwhitehemglbin (19771/PNSCaramihai (1975)Frerichs (1977J/BHSDallman (19781/KPSF3Dallman (1984)/HANESII3Reeves 1)3Owen(198 (19731/PNSAdultsWilliams m1-5 y y5-9 y10-14 y m1-6 y )- 150)- 1471)- 87)«104)- 143)- 150)- 163)«159)= 266)-21)- 140) NR ) y3-12 -NR (n =«(n 3321)= 3321)- y )- 646)=. ym/im/im/imfmfm/im/im/imfmfmmfffmfm/im/imf nr )- 767)- 1241)- 150)= 2610)- 305)- 291)- 447)= 484)- 1132)= 800)- 350)- (19811Dallman (1984)/HANESH3Kraemer 13Jacksn (1975 (1983)Meyers (1979)/HANESI3Pregnant y18-44 y18-44 y )- 227)- 216)- 21)- 33)- 742)«28)- 35)- 1914)- 1745)- 71)= 2268)- 3074)- wmengarn 1976)/TSNSGarn (1977)/NCPPTtalGarn 1200)NR 1200)- (1975)/TSNS3Gam (19811/NHANES3Current study12-71 'All differences are statistically significant (P < 0.01). Abbreviatins used: PNS, Preschl Nutritin Survey; BHS, Bgalusa Heart Study; KPSF, Kaiser-Permanente, San Francisc; TSNS, Ten State Nutritin Survey; NCPP, Natinal Cllabrative Perinatal Prgram; NR, nt reprted. 3Median hemglbin levels presented.

7 HEMOGLOBIN DIFFERENCES BETWEEN BLACKS AND WHITES 1423 (1986) and Reeves et al. (1981) have demnstrated that black children have the same r better respnse t irn therapy but still exhibit a significantly lwer hemglbin level than white children. Further, it is als pssible that the lwer transiern saturatin, higher serum ferritin, and higher erythrcyte prtprphyrin in black children culd be due t a higher prevalence f infectins r mild inflammatry cndi tins (Reeves et al. 1984). The higher erythrcyte prtprphyrin in part may be the result f higher lead expsure in black children (Pierce et al. 1977). In this study, we have demnstrated that irn status (as defined by the number f psitive irn deficiency tests) is clsely assciated with the preva lence f anemia (hemglbin < 120 g/l) in wmen (Fig. 2). The difference in hemglbin levels r preva lence f anemia between black and white wmen changed little after multivariate analysis cntrlling fr irn status and ther scidemgraphic factrs. Therefre, it is quite clear that the lwer hemglbin levels in black wmen are nt due principally t pr irn nutritin. In fact, the verall evidence frm the NHANES II sample suggests that black wmen had cmparable r slightly better irn nutritinal status than white wmen. After cnducting a stratified and multivariate analysis, cntrlling fr age, incme, parity, dietary irn intake, transferrin saturatin and serum ferritin levels, we have shwn that in a natinally represen tative sample, blacks exhibit significantly lwer he mglbin cncentratins than whites, althugh their irn stres seem t be adequate. This may suggest a ptential racial difference in irn utilizatin fr erythrpiesis. Other pssibilities include undefined genetic differences in irn utilizatin and hemglbin regulatin, differences in lean bdy mass, r ther undefined envirnmental factrs that may affect he mglbin synthesis differently in blacks. Further investigatins f racial differences in irn utilizatin and erythrpiesis are needed. T date, n studies have been designed specifically t explre racial differences in irn absrptin, mbilizatin and utilizatin in blacks acrss all age grups. Studies are als needed t identify the physilgical cnse quences, if any, f lwer hemglbin cncentratins in blacks. This study suggests that blacks have lwer hem glbin cncentratins than whites fr reasns nt related t irn nutritin. Hwever, we d nt rec mmend the adptin f race-specific hemglbin standards because it is nt yet clear that this dif ference is the result f nrmal physilgical factrs, as is the case in the differences between adults and children r between men and wmen. Mre research shuld be dne t determine whether the black-white difference in hemglbin levels might be the result f pathlgical prcesses that affect red cell prductin, r a genetic factr related t hemglbin synthesis as in the thalassemia traits. Race-specific hemglbin standards can be justified if future studies shw that the lwer hemglbin levels in blacks represent a nrmal physilgical variatin. LITERATURECITED Bazzan, G. S., Chu, A. C, Mhr, D., Bstn, E. & Willis, J. R. (1986) Racial differences in irn-related hematlgical parameters. In: Irn Frtificatin: Research n Irn Frtificatin and Irn Supplementatin Cnducted in the U.S., pp Tur Research Institute, New Orleans, LA. Caramihai, E., Karayalcin, G., Aballi, A. J. & Lanzkwshy, P. (1975 Leukcyte cunt differences in healthy white and black children 1-5 years f age. J. Pediatr. 86: Dallman, P. R., Barr, G. D., Allen, C. M. &. Shinefield, H. R. 1978) Hemglbin cncentratin in white, black and Oriental chil dren: is there a need fr separate criteria in screening fr anemia? Am. J. Clin. Nutr. 31: 377^380. Dallman, P. R., Yip, R. & Jhnsn, C. (1984) Prevalence and causes f anemia in the United States, 1976 t Am. J. Clin. Nutr. 39: 437^45. Eads, M. G., Mickelsen, O., Mrse, F. 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