Journal of the American College of Nutrition, Vol. 19, No. 3, 413-417 (2000)
Published by the American College of Nutrition
Basal Urinary Zinc/Creatinine Ratio as an Indicator of Dietary Zinc Intake in Healthy Adult Women
María L. de Portela, PhD and
Adriana R. Weisstaub, BS
Department of Nutrition and Food Sciences, School of Pharmacy and Biochemistry, University of Buenos Aires, Argentina
Address reprint requests to: Address reprint requests to: Dra María Luz P.M. de Portela, Professor of Nutrition, School of Pharmacy and Biochemistry, Junín 956, 2 p. (1113) Buenos Aires, Argentina
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ABSTRACT
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Objective: To study, in healthy women, the correlation between the basal urinary zinc/creatinine ratio and dietary zinc intake.
Subjects: A group of 36 healthy female University students was evaluated. Mean age and body weight were, respectively, 25.6±3.3 years and 54.4±7.0 kg.
Methods: Basal urine was collected; Zn was determined by AAS and Creatinine (Creat) by the Jaffe method. A nutritional survey of seven days was recorded. Mean daily dietary intake of energy (DE) and zinc (DZn) were calculated according to the INCAP and English or German Food Composition Tables, respectively.
Results: Mean dietary daily intake were as follows (±SD): Energy (kcal): 1606±570; zinc (mg): 9.1±3.8; basal urine Zn/Creat ratio: 0.41±0.24. Individual values of the Zn/Creat ratio correlated with dietary Zn (r=0.481, p=0.0339); data grouped according to ranges of dietary Zn fit the following equation: Zn/Creat=0.160±0.034 DZn (mg/day); (r=0.870, p=0.00497).
Conclusions: These results showed that the basal urinary Zn/Creat ratio could be a useful indicator of dietary Zn intake in healthy adult women.
Key words: urinary zinc, zinc intake, women
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INTRODUCTION
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Zinc (Zn) is a constituent of more than 70 metallo-enzymes and of nuclear binding proteins that act as transcription factors. Hence, it is an essential element for many metabolic functions, including growth, development and reproduction [1]. Chronic zinc deficiency was first reported in the Middle East in the early 1960s, being characterized by a slowing of physical growth, poor appetite and diminished taste acuity (hypogeusia) [2].
In the following decades marginal Zn nutritional status has also been identified in developing and developed countries in apparently healthy infants and/or children affected by low growth rate [3,4]. Other groups susceptible to Zn deficiency include pregnant women, with evidence that low concentrations of Zn in plasma can be associated with complications during pregnancy and increased risk to the fetus [4,5].
However, diagnosis of Zn nutritional status is not easy, and, in spite of the importance and increasing knowledge of zinc’s functions, there is still no single reliable indicator of Zn nutritional status. A large number of indicators have been proposed, but they offer difficulties to be considered and/or interpreted. Plasma Zn levels are usually accepted as good indicators of Zn status [6,7,8]. Urinary excretion has been documented to decrease with the development of Zn deficiency. In general, the measure of urinary Zn is carried out in twenty-four-hour urine samples, which are not easily collectable in population studies [9].
Thus, this study, at best, indicates that the zinc/creatinine ratio in basal urine may be an indicator of dietary Zn intake in healthy women.
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MATERIALS AND METHODS
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Subjects
Thirty-six university-level women, attending the School of Pharmacy and Biochemistry of Buenos Aires University, were studied during 1996. The criteria for inclusion were that women be free of diabetic disease, hypertension or other chronic diseases and that they did not take mineral supplements. The characteristics of the women were as follows (mean±SD and ranges): age (years): 25.5±3.3 (22–39); weight (kg): 54.4±7.1 (36.5–73).
Sample Collection
Each woman that gave informed consent before participation in the study received oral and written instructions for sample collection of "basal urine." Basal urine is the second urine collected in the morning with the first one discarded and after fasting from liquids and solids. Samples were collected in polypropylene containers, previously washed with nitric acid (20%) and deionized water. These were then acidified with HCl p.a. and frozen until determinations were carried out.
Laboratory Determinations
Zn was determined by atomic absorption spectrometry (AAS) using a Varian Spectrophotometer SpectrAA-20, air acetylene flame, a slit of 0.5 nm, at a wavelength 213.9 nm [10]. LaCl3 (6500 ppm) was added as an interference suppressor. All the laboratory material was previously washed with nitric acid (20%) and deionized water. Creatinine was determined by the Jaffe colorimetric method [11].
Food Intake Survey
The women received strict instructions to carry out a seven-day recorded food intake. Mean energy and protein daily intake were calculated with a computer program containing food composition data from INCAP tables [12]. Zn mean intake was calculated with a computer program, according to food Zn content data from English [13] and German [14] Tables.
Statistics
Regression analysis was carried out. Correlation coefficients between dietary zinc intake and basal urinary Zn/Creat ratio were calculated separately for the whole population and for subgroups with and without energy intake. Dietary zinc and energy intake of the two subgroups of women were compared by Student’s test [15].
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RESULTS
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Table 1 shows the mean daily intake of energy (kcal and kJ), protein (g/day and g/kg/day) and Zn (mg/day and mg/1000 kcal) in the studied women.
Adequacy of energy intake was calculated as the percentage of the requirements of energy according to the recommendations of the Technical Report of the Joint FAO/OMS/UNU Expert Consultation, 1985 [16]. To obtain the total energy requirement of each woman, the basal metabolic rate (calculated as a function of body weight) was multiplied by the correspondent factor of physical activity [16]. Our data revealed a mean percentage of adequacy of 75%. Intakes below the calculated energy requirement were found in 55.5% of our women.
Protein intake was higher than 100% of the safe level of protein intake according to FAO recommendations of 0.75 g/kg/d in all women with adequate energy intake. However, 20% of the women with energy restriction presented protein intake below FAO recommendations, ranging between 0.56 and 0.75 g/kg/day.
Distribution of the population according to Zn intake (mg/day) is shown in Fig. 1. Comparison of Zn intake with the NRC Recommended Allowances [17] showed that 75% of the women did not reach the RDA amount of 12 mg/day.
Distribution of the population according to Zn density (mg/1000 kcal) [18] is shown in Fig. 2. There was a large percentage of the women (58%) with intakes between 4 and 6 mg/1000 kcal; 31% went over the suggested intake of 6 mg/1000 kcal, but only 11% of the women did not reach 4 mg/1000 kcal ranging between 3 and 4 mg/1000 Kcal.
Mean values and ranges of Zn/Creat (mg/g) in basal urine were 0.41±0.24 (0.13–1.05). Individual values of Zn/Creat (mg/g) showed a linear correlation with dietary Zn intake (r=0.481; p=0.0339) and values were below 0.60 mg/g in 80.5% of the women (Fig. 3). Besides, data grouped according to ranges of dietary Zn intake fit the following equation (Fig. 4): Zn/Creat=0.160+0.034 dietary Zn (mg/day); (r=0.870; p=0.00497).
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Fig. 3. Relationship between the Zn/Creat ratio in basal urine and Zn dietary intake (mg/day). Dots show individual values. The line represents the regression equation (r=0.481, p=0.0339).
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Fig. 4. Relationship between Zn/creatinine ratio in basal urine and Zn dietary intake (mg/day). Data grouped according to ranges of dietary Zn intake (r=0.870, p1=0.00497).
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DISCUSSION
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The Zn content of foods in Argentina, as in other Latin American countries, is uncertain, since the National Tables do not contain data about Zn food composition. Recently, Closa and colleagues have published mineral composition of cereals and legumes that included zinc content [19], showing values similar to those published by the English and German Tables. Therefore, Zn intakes of our present report were calculated taking into account these foreign Composition Tables.
Data of the present report showed zinc intakes below NRC Recommended Allowances [17] in 75% of the women (Fig. 1), but the lowest Zn intake values were related to the energy restriction.
Values of energy and protein intake observed in the present report are in agreement with the results of previous surveys carried out in University students of Argentina [20–22]. These values represent the characteristic feeding habits of middle and high socioeconomic level people and have revealed a) a high protein intake as a consequence of the high consumption of beef, cold cuts and chicken, b) low consumption of dairy products, fruits and vegetables and c) high consumption of wheat products (bread, biscuits, pizza, pasta and the like). Yet, the consumption of cereals is voluntarily restricted, mainly among females concerned about physical appearance. These eating habits are reflected in our observed low energy intakes. Hence, when Zn intake was expressed as mg/1000 kcal there was no difference in population distribution between adequate and inadequate energy intake.
It is important to take into account that nutritional deficiency in zinc may arise from inadequate intake and/or poor availability of dietary zinc. Therefore, a large amount of Zn in the diet is no guarantee of sufficiency, and Zn intake tells us little about Zn status [17, 8]. Our studied women were in good health without clinical signs of deficiency. They presented an adequate intake of good quality protein, with frequent consumption of meat and eggs, which are good sources of available dietary Zn [8]. Moreover, consumption of fiber was low [23]. Thus, we can assume that the bioavailability of dietary Zn could be high enough to avoid clinical signs of deficiency, in spite of a low intake [24,25].
Our results regarding dietary Zn intake confirm the wide gap between the Recommended Dietary Allowances (12 mg/day) and real dietary zinc intake reported by other researchers [6, 8]. This difference stresses the need for reviewing the RDA depending on dietary Zn bioavailability [26].
On the other hand, the assessment of Zn status must be undertaken by using a battery of tests. Plasma and 24-hour urinary levels are the most common due to the easy collection of samples. Ruz and colleagues have shown that both indicators respond very quickly to changes in dietary Zn content [27]. Besides, Johnson and colleagues [9] have demonstrated in adult men, that 24-hour urinary Zn declined with decreasing Zn intake, although there was a great variability and some subjects did not show evidence of Zn depletion.
While urine Zn concentrations can be affected in various diseases, the measurement of Zn in a sample of urine collected during 24 hours can be helpful for diagnosis of Zn deficiency in healthy individuals. However, there is no data regarding Zn in basal urine expressed as Zn/Creat ratio.
Our results showed the Zn/Creat ratio in basal urine as a linear function of dietary Zn intake (r=0.870) (Fig. 4) regardless of the adequate or inadequate energy intake.
Taking into account these results, one hypothesis can be postulated to explain our results regarding Zn/Creat behavior: Zn/Creat ratio would be, as other indicators in basal urine, a function of Zn intake, which can be divided in two straight lines. The intersection or change of slope could be explained as the point at which needs are covered [28]. In Fig. 4 we can see that the change in the slope corresponds to a dietary zinc intake ranging between 10 to 12 mg/day and to a Zn/Creat ratio of 0.40 mg/g. These results suggest that the Zn/Creat ratio in basal urine could be an indicator of dietary Zn intake in healthy women.
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ACKNOWLEDGMENTS
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Supported by the University of Buenos Aires (UBA), Grant TA 060. The authors would like to thank Alicia Rovirosa for her assistance in collecting the dietary surveys, University women for their willingness to participate in the research and Mss Patricia Hoxmark for her review of the manuscript’s English.
Received April 1, 1999.
Revised February 1, 2000.
Accepted February 1, 2000.
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REFERENCES
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- Cousins R, Hempe JM: Zinc. In Brown ML (ed): "Present Knowledge in Nutrition," 6th ed. Washington, DC: Nutrition Foundation, pp 289–308, 1990.
- Prasad AS, Miale A, Farid Z, Schulert A and Sanstead HH: Zinc metabolism in patients with the syndrome of iron deficiency anemia, hypogonadism, and dwarfism. J Lab Clin Med 61: 537–549, 1963.[Medline]
- Lira PI, Ashworth AM and Morris SS: Effect of zinc supplementation on the morbidity, immune function and growth of low-birth-weight, full-term infants in northeast Brazil. Am J Clin Nutr 68 (Suppl): 418S–424S, 1998.[Abstract]
- Keen CL, Lonnerdal B, Golub MS, Olin KL, Graham TW, Uriu-Hare JY, Hendrickx AG, Gershwin ME: Effect of the severity of maternal zinc deficiency on pregnancy outcome and infant zinc status in rhesus monkeys. Pediatr Res 33: 233–241, 1993.[Medline]
- Ortega RM, Andrés P, Martínez RM, López-Sobaler AM, Quintas ME: Zinc levels in maternal milk: the influence of nutritional status with respect to zinc during the third trimester of pregnancy. Eur J Clin Nutr 51: 253–258, 1997.[Medline]
- Shrimpton R: Zinc deficiency, is it widespread but under-recognized? Focus on micronutrients, SCN News, United Nations, Subcommittee on Nutrition 9: 24–27, 1993.
- Gibson RS: Assessment of zinc status. In "Principles of Nutritional Assessment." Oxford: Oxford University Press, 1990.
- Gibson RS, Ferguson EL: Assessment of dietary zinc in a population. Am J Clin Nutr 68 (Suppl): 430S–434S, 1998.[Abstract]
- Johnson PE, Hunt CD, Milne DB, Mullen LK: Homeostatic control of zinc metabolism in men: zinc excretion and balance in men fed diets low in zinc. Am J Clin Nutr 57: 557–565, 1993.[Abstract/Free Full Text]
- "Official Methods of Analysis of the A.O.A.C." 13th ed. Washington DC: Association of Official Analytical Chemists, 1980.
- Clark LC, Thompson HL: Determination of Creatine and Creatinine. Anal Chem 21: 1218, 1959.
- Closa SJ, Oloriz M, Marchesich C: Programa Electrónico de Vigilancia Alimentaria Nacional (VAN-UNLU). (Abstract 113-IX). Congreso Latinoamericano de Nutrición. San Juan (Puerto Rico), September 22–26, 1991.
- McCance RA, Widdowson EM: "The Composition of Foods," 5th ed. London: Royal Society of Chemistry, Ministry of Agriculture, Fisheries and Food, 1993.
- Souci S, Fachmann W, Kraut H: "Die Zusammensetzung der Lebensmittel Nahrwert-Tabellen." Stuttgart: Wissenschaftliche Verlagsesellschaft, 1979.
- Sokal RR, Rohi FJ: "Biometry: The Principles and Practice of Statistics in Biological Research." San Francisco: W.H. Freeman and Company, 1969.
- Necesidades de Energía y de Proteinas. Informe de una Reunión Consultiva Conjunta FAO/WHO/UNU de Expertos, Informe Técnico 724, OMS, Ginebra, 1985.
- National Academy of Sciences: "Recommended Dietary Allowances," 10th ed. Washington, DC: National Academy Press, 1989.
- Metas nutricionales y guías de alimentación para América Latina: Archivos Latinoamericanos de Nutrición, vol XXXVIII, pp 410, 1987.
- Closa SJ, de Landeta MC, Andérica DA, Larroquette DO, Alzogaray B: Contenido de nutrientes minerales en materias primas y productos procesados derivados de cereales y leguminosas: II: Composición en elementos minerales. Archivos Latinoamericanos de Nutrición, 46: 250–252, 1996.[Medline]
- Boyer P, Portela MLPM, Río ME y Sanahuja JC: Evaluación del estado nutricional de una población estudiantil. Medicina (Buenos Aires, Argentina), 47: 51–56, 1987.
- Rovirosa A, Dupraz H, de Portela ML, Río ME: Ingesta de nutrientes en una poblacion estudiantil masculina de la Universidad de Buenos Aires. Revista Farmacéutica (Buenos Aires, Argentina) 133: 53–61, 1993.
- Pacin A, Martínez E, Pita Martín de Portela ML, Neira MS: Consumo de alimentos e ingesta de algunos nutrientes en la población de la Universidad Nacional De Luján, Argentina. Archivos Latinoamericanos de Nutrición 49: 31–39, 1999.[Medline]
- López L, García M, Giraldez S, Ortega Soler CR, de Portela ML: Cálculo de la digestibilidad proteica de la alimentación de gestantes del Gran Buenos Aires. (Abstract) VII Congreso Argentino de Graduados en Nutrición, Buenos Aires, 4–7 de junio, 1996.
- Rosado J L, Lopez P, Morales M, Munoz E, Allen LH: Bioavailability of Energy, Nitrogen, Fat, Zinc, Iron and Calcium From Rural and Urban Mexican Diets. British J of Nutr 68: 45–58, 1992.
- World Health Organization: Trace elements in human health and nutrition. Geneva: World Health Organization, 1996.
- King JC: Recommened dietary intakes for trace elements. 10th International Symposium on Trace Elements in Man and Animal, Evian (France), May 2–7, 1999.
- Ruz M, Cavan KR, Bettger WJ, Fisher F and Gibson RS: Indices of iron and copper status during experimentally induced, marginal Zinc deficiency in humans. Biol Trace Element Res 34: 197–211, 1992.[Medline]
- Zeni S, Morasso M del C, Portela ML, Rio ME: Relación Hierro/Creatinina en orina basal: su utilidad como indicador del estado nutricional respecto del hierro. Medicina (Buenos Aires) 46: 64–68, 1986.
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ABSTRACT
INTRODUCTION
