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Characterization of the Regional Distribution of Selenium in Chile Using Selenium in Hens' Eggs as a Monitor
J. Trace Elements Med. Bio!. Vo!. 9, pp. 156-159 (1995)
Characterization of the Regional Distribution of Selenium in Chile Using Selenium in Hens' Eggs as a Monitor M. RUZ, J. CODOCEO, S. HURTADO, L. MUNOZ AND N. GRAS Department of Nutrition, Faculty of Medicine, University of Chile and The Chilean Nuclear Energy Commission, Santiago, Chile (Received March/May 1995)
Summary
Regional distribution of selenium (Se) in Chile was investigated by using the concentration of Se in hens' eggs as a monitor. Forty-one locations along the entire lenght of the country were sampled. Average (± SD) egg-white Se content (mg/kg dry) was 0.79 ± 0.41, range 0.22-2.23. Corresponding yolk Se values were, mean O.Sl ± 0.43, (mg/kg dry) range 0.26-2.23. Locations grouped in five main areas, according to their geographicclimatic characteristics, showed significant differences regarding both egg-white Se and yolk Se. Analyzed dietary Se intake from two distinct areas reflected the trends observed in the Se content of egg fractions from such regions. These data support the utilization of the concentration of Se in hens' eggs as a useful monitor of dietary selenium consumed by selected populations.
Keywords: Selenium, Chile, selenium distribution, biological monitor. Introduction
In recent years, the study of the Se situation of populations around the world has grown in interest. This is a consequence of the recognition of both naturally-occurring Se-deficiency and Se-excess conditions. On one hand, Keshan's disease is the most severe condition associated with Se-deficiency. On the other end, manifestations of Se-toxicity in areas of China and Venezuela have been reported. Selenium imbalance can affect human health in varying degrees depending on the magnitude of the deviation from the "safe-range" (1-3). Se has, therefore, been a matter of concern to groups with quite distinct interests such as: nutritionists, chemists, toxicologists, cardiologists, and more recently, oncologists. Among the main determining factors of Se status is the content of Se in foods, which in tum is strongly affected by certain characteristics of soils. Particularly relevant to the Se content of soils are: pH; Se fixation capacReprint requests to: Prof. Dr. Manuel Ruz, Department of Nutrition, Faculty of Medicine, University of Chile, Independencia 1027, Santiago, Chile. © 1995 by Gustav Fischer Verlag Stuttgart· Jena . New York
ity; and microbial activity. Climate and fertilizers also influence the final concentration of Se in foods (4-5). As a consequence, the content of Se in foods-especially those of vegetable origin-may vary over such a wide range that the utilization of food composition tables becomes useless. In general terms, the best sources of dietary Se are seafood and meats; grains are highly variable depending on soil conditions; fruits and vegetables do not contribute significantly to the total intake (5). Variations in selenium in soils and foods are important. They determinate that certain geographic locations around the world can be classified as areas of "low" and "high" Se. Areas of "low" Se have been identified in various nations: New Zealand; Australia; Finland; Egypt; and China. High-Se areas have been found in: Venezuela;, China; South Africa; regions of the former USSR; Australia; Ireland; Israel; and in parts of the United States. China presents a unique situation with areas of extremely low Se, such as those where Keshan's disease has been observed, as well as areas where Se toxicity occurs (6-7). In Chile, a lack of infOlmation regarding the Se con-
Selenium distribution in Chile
tent of foods, usual Se intakes, and Se status of individuals existed prior to this investigation. Chile is a long (4329 km) and narrow country (177 km wide -from the Andes to the Pacific Ocean- on the average). The maximum width is 390 km, and the minimum is 90 km. The presynce of a wide variety of geographic-climatic characteristics may result in areas of "low" or "high" Se. For instance, Northern Chile is mainly desertic, Central Chile is temperate, and Southern Chile is cold-rainy. The type of soil in these regions is also distinct. In addition, in some areas (particularly in the North) there are several situations -potentially relevant for Se status- such as mineraI deposits (Cu, Ag, Li, Mo), and areas of high arsenic levels, which are not common in the rest of the country
157
ured in a high resolution gamma spectrometer 01-12). During the entire process of handling and analysis of samples, special care was taken to avoid contamination (13). Precision and accuracy of the technique were checked by repeated determinations of Se in the reference material whole egg powder (RM 8415) of the US National Institute of Standards and Technology. The mean value was 1.42 ± 0.10 mg/kg compared to certified value of 1.39 mg/kg. Descriptive statistics and one-way Analysis of Variance, followed by the Newman-Keuls test, were performed to evaluate the results (14).
(8).
The use of monitors of Se can be very useful in exploratory studies to characterize variations in the Se intake of populations. Among the monitors used are the following: red blood celIs, plasma, urine; hair, nails, and breast milk (9). Bratter et a\. (10) have also proposed the use of hens' eggs as a valuable Se monitor, since it can be used to distinguish not only the amount of selenium consumed but also its main form, i.e., selenomethionine vs. inorganic forms. In the present study, Se distribution in distinct regions of Chile was investigated by determining the concentration of Se in free-range hens' eggs as a Se monitor. Further, dietary Se data collected in two distinct geographical areas were compared and related to Se levels in the Se monitor.
Materials and Methods
Egg samples were collected from families which were known not to feed their hens commercial foodstuffs. A total of 41 locations along the lenght of the entire country was sampled. At each location, samples were obtained from three different suppliers to take intra-location variation into account. The arithmetic mean was calculated from the three individual determinations, and the result was considered as the representative value of the given location. Egg white and yolk were separated, handled individually, and analyzed. Egg samples were ground and homogenized in a " Clean Laboratory" at the Chilean Nuclear Energy Commission. Samples were lyophilized and stored until analysis. The Se content was determined by instrumental neutron activation analysis (INAA). The samples were irradiated for 24 h at a thermal neutron flux of 10 13 n . cm- 2 • S-I. After 15 days decay, the radiation gamma from the long-lived radio nuclide 75Se was meas-
Results
The content of Se in both egg fractions showed significant inter-location variations. Egg-white Se-content ranged from 0.22 to 2.23 mg/kg dry, and Se in yolk from 0.26 to 2.23 mg/kg. By using the results of Se and moisture (data not shown) obtained in these samples, the total content of Se in whole egg can then be calculated. Average (± S.D.) whole egg Se was 0.246 ± 0.142 mg/kg wet (range 0.085 to 0.644 mg/kg wet). Intra-location variation (data not shown), evaluated as the coefficient of variation of the three samples analyzed at each location, was 12.1 % for egg white Se and 12.8% for yolk Se. In order to alIow a better description and interpretation of the results, the 41 locations were later grouped, into five representative areas according to their geographic-climatic characteristics: a) Far North, b) North,
Table I. Selenium content (mg/kg) in egg white and yolk from five geographical areas of Chile. Areas
Number of locations
Se* egg white
yolk
Far north
14
1.09 ± 0.50'
1.10 ± 0.49'
North
3
0.69±0.II"
0.64 ± 0.08""
Central
5
0.59 ± 0.17""
0.55 ± 0.21 ""
South
12
0.55 ± 0.26''''
0.58 ± 0.20""
Far south All
7 41
0. 8 \ + 0.25,e 0.79 ± 0.41
0.90 + 0.47" 0.81 ± 0.43
p=0.006**
p=0.008**
* Mean±S.D.**ANOVA Values not showing a common superscript in the same column are significantly different (p< 0.05)
158
M. Ruz, J. Codoceo, S. Hurtado, L. Munoz and N. Gras
c) Central, d) South, e) Far South. The means ± S.D. of Se contents of egg-white and yolk in the five areas are presented in Table 1. One-way analysis of variance demonstrated statistical differences among areas regarding both egg white and yolk. The average egg-white-Se / yolk-Se ratio -calculated on the dry weight basis- was 1.0, without significant inter-area differences. The association between egg-white Se and observed Se daily intakes by residents of the areas studied is depicted in Figure 1 . Plotted data have been taken from unpublished results obtained by our research group and from results published by Bratter et al. (10) in Venezuela.
Discussion
Since the main determinant of Se status is Se intake, a first approach to the Se condition of population groups can be accomplished by using monitors of Se consumption. In this context, the use of the Se content of hens' eggs as a monitor offers important advantages (10). In addition to those related to low cost and easy access, selenium contained in hens'eggs is dependent on both the amount and the main form of Se in the diet. Since egg white proteins origin'!-te in the oviduct, whereas yolk proteins are synthesized in the liver, the former is related to the selenomethionine form in the diet, and the latter to selenite (15-17). Our results in egg-white and yolk showed a wide variation regarding Se content. In both fractions the highest value represents approximately eight times that of the lowest. A similar picture is obtained when these results in isolated fractions are translated into the total Se content in whole egg. The max/min ratio of Se content is markedly
8
116. 11
o
t:JtI( "hilo So (/'w/: I
6
c
2
Se-intakc (Jig/d) A • CHILE ISOUTHI
C • VENEZUELA (CARACASI
I • CHILE IFAA NORTHI
0 • VENEZUELA ISELENIFEROUS AREAl
Figure l.Relationship between selenium intake (J..lg/d) and selenium content in egg white (J..lg/g dry). Comparison of regional data of Chile (current work) and Venezuela (10).
higher than the corresponding ratio of another trace element, zinc. This has important implications for the use of food composition tables to calculate total intake of Se. Unless the Se content offoods produced locally is included into the database, the results will probably not be reliable. Differences regarding Se content in the eggs obtained in five main regions of Chile were evident. Mean content from the Far North was consistently higher than that in the remaining areas. In other words, in the case of Chile, an accurate estimation of Se intake must employ, at least two datasets of Se in foods. In order to expand on the observations made in Venezuela on the association between Se intake and egg-white Se (10), dietary data obtained in two Chilean cities, by direct analysis of 24-h duplicate diet composites (unpublished data) were related to the level of Se in egg-white from the corresponding areas. The association between these two variables was maintained throughout a wide range of Se intakes (Figure 1). These findings provide further support for the use of the concentration of Se in egg fractions as a monitor of dietary Se consumed by selected popUlations. In terms of comparative capacity (egg-white Se 1's. yolk Se) to estimate regional dietary Se intakes, the response is dependent on the usual levels and the form of Se in the diet. At the levels of Se intake observed in the areas studied in Chile, i.e., 50-100 Ilg per day on average, both fractions presented a similar picture. At higher intakes, however, such as those observed in the seleniferous areas of Venezuela (500-600 Ilg per day), where selenomethionine is the predominant form of dietary Se, egg white showed to be more sensitive than egg yolk (10). In conclusion, the use of the determination of Se in egg fractions from free-range hens provides an inexpensive and non-invasive means for approximating regional dietary Se intakes. This can be a valuable tool for preliminary data collection. If taken into account,. the results can be helpful in the optimization of resources and efforts for more comprehensive investigations of the selenium status of selected populations.
Acknowledgements
We are indebted to Mrs Nancy Linero for her invaluable participation. We wish to thank Mr Juan Troncoso, MT for his collaboration and the authorities of the Hospital Regional de Iquique. Further, we want to express our gratitude to Mr Jose Zamora, MT, and the authorities of the Department of Basic Sciences of the Faculty of Medicine, Univesidad de La Frontera, Temuco, for their contribution. This study was funded by FONDECYT, Research Grant 1931030.
Selenium distribution in Chile
References I. ROBINSON MF. (1982) Clinical effects of selenium deficiency and excess. In: Clinical, biochemical and nutritional aspects of trace elements (Prasad AS, ed.) Alan R Liss Inc, New York, NY. pp.323-343 2. JAFFE W. (1992) Selenio, un elemento esencial y t6xico. Datos de Latinoamerica. Arch. Latinoamer Nutr. 42, 90-93 3. SOLOMONS N.W. AND RUZ M. (1990) Zinc and other trace metals. In: Tropical and geographical medicine (Warren KS , Mahmoud AAF. eds.) 2nd edition. McGraw-Hili Book Co. New York, NY. pp. 1083-1094 4. GISSEL-NIELSEN G., GUPTA U.c., LAM AND M AND WESTERMARCK T. (1984) Selenium in soils and plants and its importance in livestock and human nutrition. Adv. Agronom. 37, 397-460 5. MASON AC. (1988) Selenium. In: Trace minerals in foods (Smith KT, ed.) Marcel Dekker Inc, New York, NY. pp. 325356 6. LEVANDER O.A. (1987) A global view of selenium nutrition. Ann. Rev. Nutr. 7, 227-250 7. DlPLOCK A.T. (1987) Trace elements in human health with special reference to selenium. Am. J. Clin. Nutr. 45,1313-1322. 8. PEN A L., JAMETT A., SANTANDER M., GRAS N. AND MUNOZ L. (1992) Concentraci6n de elementos traza en nifios del norte de Chile. Rev. Med. Chile 120, 20-24 9. BRATTER P., NEGRETTI DE BRATTER VE., OLIVER W. AND JAFFE W. (1993) Selenium in human monitors related to dietary intake levels in Venezuela. J. Trace Elem. Electrolytes Health Dis. 7, 111-112
159
10. BRATTER P. , NEGRETTI DE BRATTER VE, ROSIK U. AND MENDEZ C (1988) The utilization of hens' eggs as a selenium monitor in epidemiological studies. In: Trace Elements in Man and Animals 6 (Hurley L.S., Keen C.L., Lonnerdal B., Rucker R.B., eds.) Plenum Press, New York. pp.167-169 II. GRAS N., GALLARDO T., THIECK M. AND MUNOZ L. (1991) A study of trace elements in Chilean seafoods. International conference on Modem Trends in Activation Analysis, Vienna. 12. HEYDORN K. AND GRIEPINK B. (1990) Selection of reference methods for the determination of selenium in biological materials. Fresenius J. Anal. Chern. 338, 287-292 13. GRAS N., MUNOZ L., CASSORLA V AND CASTILLO P. (1992) Homogeneity preliminary study of in-house reference material using neutron activation analysis and X-ray fluorescence. Proceedings of the Fifth International Symposium on Biological and Environmental Reference Materials. Aachen, Germany. 14. SNEDECOR G.w. AND COCHRAN w.G. (1980) Statistical methods, 7th edition. The Iowa State University Press, Ames, Iowa. 15. LATSHAW J.D. (1975) Natural and selenite selenium in the hen and egg. J. Nutr. 105,32-37 16. MOKSNES K. AND NORHEIM G. (1982) Seleniumconcentration in tissues and eggs of growing and laying chickens fed sodium selenite at different levels. Acta Vet. Scand. 23, 368379 17. MOKSNES K. (1983) Selenium deposition in tissues and eggs of laying hens given surplus of selenium as selenomethionine. Acta Vet. Scand. 24, 34-44
Characterization of the Regional Distribution of Selenium in Chile Using Selenium in Hens' Eggs as a Monitor M. RUZ, J. CODOCEO, S. HURTADO, L. MUNOZ AND N. GRAS Department of Nutrition, Faculty of Medicine, University of Chile and The Chilean Nuclear Energy Commission, Santiago, Chile (Received March/May 1995)
Summary
Regional distribution of selenium (Se) in Chile was investigated by using the concentration of Se in hens' eggs as a monitor. Forty-one locations along the entire lenght of the country were sampled. Average (± SD) egg-white Se content (mg/kg dry) was 0.79 ± 0.41, range 0.22-2.23. Corresponding yolk Se values were, mean O.Sl ± 0.43, (mg/kg dry) range 0.26-2.23. Locations grouped in five main areas, according to their geographicclimatic characteristics, showed significant differences regarding both egg-white Se and yolk Se. Analyzed dietary Se intake from two distinct areas reflected the trends observed in the Se content of egg fractions from such regions. These data support the utilization of the concentration of Se in hens' eggs as a useful monitor of dietary selenium consumed by selected populations.
Keywords: Selenium, Chile, selenium distribution, biological monitor. Introduction
In recent years, the study of the Se situation of populations around the world has grown in interest. This is a consequence of the recognition of both naturally-occurring Se-deficiency and Se-excess conditions. On one hand, Keshan's disease is the most severe condition associated with Se-deficiency. On the other end, manifestations of Se-toxicity in areas of China and Venezuela have been reported. Selenium imbalance can affect human health in varying degrees depending on the magnitude of the deviation from the "safe-range" (1-3). Se has, therefore, been a matter of concern to groups with quite distinct interests such as: nutritionists, chemists, toxicologists, cardiologists, and more recently, oncologists. Among the main determining factors of Se status is the content of Se in foods, which in tum is strongly affected by certain characteristics of soils. Particularly relevant to the Se content of soils are: pH; Se fixation capacReprint requests to: Prof. Dr. Manuel Ruz, Department of Nutrition, Faculty of Medicine, University of Chile, Independencia 1027, Santiago, Chile. © 1995 by Gustav Fischer Verlag Stuttgart· Jena . New York
ity; and microbial activity. Climate and fertilizers also influence the final concentration of Se in foods (4-5). As a consequence, the content of Se in foods-especially those of vegetable origin-may vary over such a wide range that the utilization of food composition tables becomes useless. In general terms, the best sources of dietary Se are seafood and meats; grains are highly variable depending on soil conditions; fruits and vegetables do not contribute significantly to the total intake (5). Variations in selenium in soils and foods are important. They determinate that certain geographic locations around the world can be classified as areas of "low" and "high" Se. Areas of "low" Se have been identified in various nations: New Zealand; Australia; Finland; Egypt; and China. High-Se areas have been found in: Venezuela;, China; South Africa; regions of the former USSR; Australia; Ireland; Israel; and in parts of the United States. China presents a unique situation with areas of extremely low Se, such as those where Keshan's disease has been observed, as well as areas where Se toxicity occurs (6-7). In Chile, a lack of infOlmation regarding the Se con-
Selenium distribution in Chile
tent of foods, usual Se intakes, and Se status of individuals existed prior to this investigation. Chile is a long (4329 km) and narrow country (177 km wide -from the Andes to the Pacific Ocean- on the average). The maximum width is 390 km, and the minimum is 90 km. The presynce of a wide variety of geographic-climatic characteristics may result in areas of "low" or "high" Se. For instance, Northern Chile is mainly desertic, Central Chile is temperate, and Southern Chile is cold-rainy. The type of soil in these regions is also distinct. In addition, in some areas (particularly in the North) there are several situations -potentially relevant for Se status- such as mineraI deposits (Cu, Ag, Li, Mo), and areas of high arsenic levels, which are not common in the rest of the country
157
ured in a high resolution gamma spectrometer 01-12). During the entire process of handling and analysis of samples, special care was taken to avoid contamination (13). Precision and accuracy of the technique were checked by repeated determinations of Se in the reference material whole egg powder (RM 8415) of the US National Institute of Standards and Technology. The mean value was 1.42 ± 0.10 mg/kg compared to certified value of 1.39 mg/kg. Descriptive statistics and one-way Analysis of Variance, followed by the Newman-Keuls test, were performed to evaluate the results (14).
(8).
The use of monitors of Se can be very useful in exploratory studies to characterize variations in the Se intake of populations. Among the monitors used are the following: red blood celIs, plasma, urine; hair, nails, and breast milk (9). Bratter et a\. (10) have also proposed the use of hens' eggs as a valuable Se monitor, since it can be used to distinguish not only the amount of selenium consumed but also its main form, i.e., selenomethionine vs. inorganic forms. In the present study, Se distribution in distinct regions of Chile was investigated by determining the concentration of Se in free-range hens' eggs as a Se monitor. Further, dietary Se data collected in two distinct geographical areas were compared and related to Se levels in the Se monitor.
Materials and Methods
Egg samples were collected from families which were known not to feed their hens commercial foodstuffs. A total of 41 locations along the lenght of the entire country was sampled. At each location, samples were obtained from three different suppliers to take intra-location variation into account. The arithmetic mean was calculated from the three individual determinations, and the result was considered as the representative value of the given location. Egg white and yolk were separated, handled individually, and analyzed. Egg samples were ground and homogenized in a " Clean Laboratory" at the Chilean Nuclear Energy Commission. Samples were lyophilized and stored until analysis. The Se content was determined by instrumental neutron activation analysis (INAA). The samples were irradiated for 24 h at a thermal neutron flux of 10 13 n . cm- 2 • S-I. After 15 days decay, the radiation gamma from the long-lived radio nuclide 75Se was meas-
Results
The content of Se in both egg fractions showed significant inter-location variations. Egg-white Se-content ranged from 0.22 to 2.23 mg/kg dry, and Se in yolk from 0.26 to 2.23 mg/kg. By using the results of Se and moisture (data not shown) obtained in these samples, the total content of Se in whole egg can then be calculated. Average (± S.D.) whole egg Se was 0.246 ± 0.142 mg/kg wet (range 0.085 to 0.644 mg/kg wet). Intra-location variation (data not shown), evaluated as the coefficient of variation of the three samples analyzed at each location, was 12.1 % for egg white Se and 12.8% for yolk Se. In order to alIow a better description and interpretation of the results, the 41 locations were later grouped, into five representative areas according to their geographic-climatic characteristics: a) Far North, b) North,
Table I. Selenium content (mg/kg) in egg white and yolk from five geographical areas of Chile. Areas
Number of locations
Se* egg white
yolk
Far north
14
1.09 ± 0.50'
1.10 ± 0.49'
North
3
0.69±0.II"
0.64 ± 0.08""
Central
5
0.59 ± 0.17""
0.55 ± 0.21 ""
South
12
0.55 ± 0.26''''
0.58 ± 0.20""
Far south All
7 41
0. 8 \ + 0.25,e 0.79 ± 0.41
0.90 + 0.47" 0.81 ± 0.43
p=0.006**
p=0.008**
* Mean±S.D.**ANOVA Values not showing a common superscript in the same column are significantly different (p< 0.05)
158
M. Ruz, J. Codoceo, S. Hurtado, L. Munoz and N. Gras
c) Central, d) South, e) Far South. The means ± S.D. of Se contents of egg-white and yolk in the five areas are presented in Table 1. One-way analysis of variance demonstrated statistical differences among areas regarding both egg white and yolk. The average egg-white-Se / yolk-Se ratio -calculated on the dry weight basis- was 1.0, without significant inter-area differences. The association between egg-white Se and observed Se daily intakes by residents of the areas studied is depicted in Figure 1 . Plotted data have been taken from unpublished results obtained by our research group and from results published by Bratter et al. (10) in Venezuela.
Discussion
Since the main determinant of Se status is Se intake, a first approach to the Se condition of population groups can be accomplished by using monitors of Se consumption. In this context, the use of the Se content of hens' eggs as a monitor offers important advantages (10). In addition to those related to low cost and easy access, selenium contained in hens'eggs is dependent on both the amount and the main form of Se in the diet. Since egg white proteins origin'!-te in the oviduct, whereas yolk proteins are synthesized in the liver, the former is related to the selenomethionine form in the diet, and the latter to selenite (15-17). Our results in egg-white and yolk showed a wide variation regarding Se content. In both fractions the highest value represents approximately eight times that of the lowest. A similar picture is obtained when these results in isolated fractions are translated into the total Se content in whole egg. The max/min ratio of Se content is markedly
8
116. 11
o
t:JtI( "hilo So (/'w/: I
6
c
2
Se-intakc (Jig/d) A • CHILE ISOUTHI
C • VENEZUELA (CARACASI
I • CHILE IFAA NORTHI
0 • VENEZUELA ISELENIFEROUS AREAl
Figure l.Relationship between selenium intake (J..lg/d) and selenium content in egg white (J..lg/g dry). Comparison of regional data of Chile (current work) and Venezuela (10).
higher than the corresponding ratio of another trace element, zinc. This has important implications for the use of food composition tables to calculate total intake of Se. Unless the Se content offoods produced locally is included into the database, the results will probably not be reliable. Differences regarding Se content in the eggs obtained in five main regions of Chile were evident. Mean content from the Far North was consistently higher than that in the remaining areas. In other words, in the case of Chile, an accurate estimation of Se intake must employ, at least two datasets of Se in foods. In order to expand on the observations made in Venezuela on the association between Se intake and egg-white Se (10), dietary data obtained in two Chilean cities, by direct analysis of 24-h duplicate diet composites (unpublished data) were related to the level of Se in egg-white from the corresponding areas. The association between these two variables was maintained throughout a wide range of Se intakes (Figure 1). These findings provide further support for the use of the concentration of Se in egg fractions as a monitor of dietary Se consumed by selected popUlations. In terms of comparative capacity (egg-white Se 1's. yolk Se) to estimate regional dietary Se intakes, the response is dependent on the usual levels and the form of Se in the diet. At the levels of Se intake observed in the areas studied in Chile, i.e., 50-100 Ilg per day on average, both fractions presented a similar picture. At higher intakes, however, such as those observed in the seleniferous areas of Venezuela (500-600 Ilg per day), where selenomethionine is the predominant form of dietary Se, egg white showed to be more sensitive than egg yolk (10). In conclusion, the use of the determination of Se in egg fractions from free-range hens provides an inexpensive and non-invasive means for approximating regional dietary Se intakes. This can be a valuable tool for preliminary data collection. If taken into account,. the results can be helpful in the optimization of resources and efforts for more comprehensive investigations of the selenium status of selected populations.
Acknowledgements
We are indebted to Mrs Nancy Linero for her invaluable participation. We wish to thank Mr Juan Troncoso, MT for his collaboration and the authorities of the Hospital Regional de Iquique. Further, we want to express our gratitude to Mr Jose Zamora, MT, and the authorities of the Department of Basic Sciences of the Faculty of Medicine, Univesidad de La Frontera, Temuco, for their contribution. This study was funded by FONDECYT, Research Grant 1931030.
Selenium distribution in Chile
References I. ROBINSON MF. (1982) Clinical effects of selenium deficiency and excess. In: Clinical, biochemical and nutritional aspects of trace elements (Prasad AS, ed.) Alan R Liss Inc, New York, NY. pp.323-343 2. JAFFE W. (1992) Selenio, un elemento esencial y t6xico. Datos de Latinoamerica. Arch. Latinoamer Nutr. 42, 90-93 3. SOLOMONS N.W. AND RUZ M. (1990) Zinc and other trace metals. In: Tropical and geographical medicine (Warren KS , Mahmoud AAF. eds.) 2nd edition. McGraw-Hili Book Co. New York, NY. pp. 1083-1094 4. GISSEL-NIELSEN G., GUPTA U.c., LAM AND M AND WESTERMARCK T. (1984) Selenium in soils and plants and its importance in livestock and human nutrition. Adv. Agronom. 37, 397-460 5. MASON AC. (1988) Selenium. In: Trace minerals in foods (Smith KT, ed.) Marcel Dekker Inc, New York, NY. pp. 325356 6. LEVANDER O.A. (1987) A global view of selenium nutrition. Ann. Rev. Nutr. 7, 227-250 7. DlPLOCK A.T. (1987) Trace elements in human health with special reference to selenium. Am. J. Clin. Nutr. 45,1313-1322. 8. PEN A L., JAMETT A., SANTANDER M., GRAS N. AND MUNOZ L. (1992) Concentraci6n de elementos traza en nifios del norte de Chile. Rev. Med. Chile 120, 20-24 9. BRATTER P., NEGRETTI DE BRATTER VE., OLIVER W. AND JAFFE W. (1993) Selenium in human monitors related to dietary intake levels in Venezuela. J. Trace Elem. Electrolytes Health Dis. 7, 111-112
159
10. BRATTER P. , NEGRETTI DE BRATTER VE, ROSIK U. AND MENDEZ C (1988) The utilization of hens' eggs as a selenium monitor in epidemiological studies. In: Trace Elements in Man and Animals 6 (Hurley L.S., Keen C.L., Lonnerdal B., Rucker R.B., eds.) Plenum Press, New York. pp.167-169 II. GRAS N., GALLARDO T., THIECK M. AND MUNOZ L. (1991) A study of trace elements in Chilean seafoods. International conference on Modem Trends in Activation Analysis, Vienna. 12. HEYDORN K. AND GRIEPINK B. (1990) Selection of reference methods for the determination of selenium in biological materials. Fresenius J. Anal. Chern. 338, 287-292 13. GRAS N., MUNOZ L., CASSORLA V AND CASTILLO P. (1992) Homogeneity preliminary study of in-house reference material using neutron activation analysis and X-ray fluorescence. Proceedings of the Fifth International Symposium on Biological and Environmental Reference Materials. Aachen, Germany. 14. SNEDECOR G.w. AND COCHRAN w.G. (1980) Statistical methods, 7th edition. The Iowa State University Press, Ames, Iowa. 15. LATSHAW J.D. (1975) Natural and selenite selenium in the hen and egg. J. Nutr. 105,32-37 16. MOKSNES K. AND NORHEIM G. (1982) Seleniumconcentration in tissues and eggs of growing and laying chickens fed sodium selenite at different levels. Acta Vet. Scand. 23, 368379 17. MOKSNES K. (1983) Selenium deposition in tissues and eggs of laying hens given surplus of selenium as selenomethionine. Acta Vet. Scand. 24, 34-44