Dietary intake of zinc and selenium in Turkey

Transcription

1 Journal of Radioanalytical and Nuclear Chemistry, Vol. 249, No. 1 (2001) Dietary intake of zinc and selenium in Turkey N. K. Aras, 1 * A. Nazli, 1 W. Zhang, 2 A. Chatt 2 1 Fatih University, Istanbul, Turkey 2 Department of Chemistry, Dalhousie University, Halifax, NS, B3H 4J3, Canada (Received December 13, 2000) It is known that in the Turkish soil Se and Zn concentrations are somewhat lower than in other countries. Lower zinc intake causes significant health problems mostly at rural areas. Six different population groups, total of 55 subjects, consisting of children, people from rural areas, university students and staff members were selected and diet samples were collected by duplicate portion technique. Bread and flour samples were collected from six different bakeries in Ankara. Zinc, selenium and other trace elements in these samples were analyzed mostly by INAA. Daily dietary zinc intake differs among different groups, ranging 5 13 mg Zn/day, and for all cases, it is lower than RDA value of 15 mg Zn/day. Similarly, selenium daily intake is around µg Se/day, which is also lower than RDA value of µg Se/day. Introduction Zinc is one of the most important essential trace elements which forms a part of the many enzymes. It plays important roles in synthesis and decomposition of carbohydrates, proteins, lipids and nucleic acids. 1 Selenium is also essential component of the daily diet, and is important for indigenous antioxidative defence system and immunological defence. Inadequate intake of selenium is inversely linked to cardio-vascular diseases, cancer and other degenerative diseases. Selenium concentration in food is strongly depended on soil concentration and the availability in the area of origin and is also affected by cooking loses. Studies show that, in Turkey the daily dietary intake of zinc and selenium is in general below the recommended daily allowance, RDA, values. 2 4 This causes significant health problems mostly at rural sections. 5 Therefore, it is important to measure zinc and selenium concentrations in total diet and staple foods, and calculate daily dietary intakes. In the last decades, many countries have shown an increasing interest on the concentrations of trace elements in food and diet and started programs in order to monitor the trace element contents. 6 There are not many studies in Turkey on the trace elements in diet. 3,4 Wheat is by far the most used staple food in Turkey. Estimates show that about 400 g wheat or wheat products are used daily by the average Turkish people and much of it in the form of bread. 7 In this work we present zinc and selenium data for total diet, bread and flour measured by instrumental neutron activation analysis (INAA). Experimental Collection of diet, bread and flour samples Some parameters such as socio-economical, cultural and regional variations have been considered for the selection of sampling sites. For the purpose of diet collection we have selected six different population groups. The first group is a rural low income group composed of six subjects selected from the population living in three villages near Ankara, Lalahan. These are named in short as LAL samples. The main diet of the families is mostly of carbohydrate origin, what they grow themselves and preserve during the summer. 3 The second population group is an urban middleupper income group in Ankara, who have at least high school education, and most have university degrees. All of these subjects were either members of Middle East Technical University, METU, or their close relatives. Since Ankara is a large metropolitan city, it receives vegetables and fruits from every part of the country. Therefore the food taken is not typical of Ankara but is representative of large cities of Turkey. 3 Third group was from Ankara University Hospital. These subjects were relatives of the patients staying in the hospital. Their diets, which were collected during winter time, were composed of mostly regular hospital diet, plus a few extras from home or market, assigned as winter diet or W samples. A second collection were carried out at the same hospital during summertime and named as S samples. 4 Duplicate diet from Ankara University kindergarten were collected and named CHD. 8 They were 4 7 years old, 5 girls and one boy. * namikaras@ixir.com /2001/USD Akadémiai Kiadó, Budapest 2001 Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht

2 Last two duplicate diet samples, FU-F and FU-M, were collected from the members of Fatih University, during the summer of They were years old female and male subjects. Samples were collected by duplicate portion technique. In this technique, everything that a subject had consumed during a 3-day period was collected. The samples were homogenized with a homogenizer having titanium blades and then freeze dried. Details of experimental conditions were given earlier. 3,4 Bread and flour samples were collected in 1995 with the help of Ankara Bakeries Associations. 9 Six major bakeries in Ankara were selected and the most consumed white bread and flour samples were collected. In each case, three fresh bread samples were collected, dried for eight hours at 50 C then powdered with a homogenizer. Analysis of the samples Zinc and selenium in these samples were analyzed mostly by instrumental neutron activation analysis, using nuclear reactors at dekmece Nuclear Research Center, Istanbul, 3 Massachusetts Institute of Technology, 4 and Dalhousie University, Halifax Canada. 9 Zinc was determined by irradiation of mg dry diet samples for 4 8 hours and counting the gammarays with HPGe detector after about day cooling. For the determination of Se, Slowpoke Reactor at the Dalhousie University was used. About 700 mg flour, 250 mg bread samples and several SRM s were used in these experiments. The neutron flux was n. cm 2. s 1. The samples were subjected to 30- second irradiation, followed by 10-second cooling and 40-second counting of the 162 kev gamma-rays coming from 77m Se with 17.0 seconds half-life. Results and discussion The zinc concentrations in total diet, along with daily intake of dry ingredients and RDA values are given in Table 1. The average daily diet intake of METU subjects is much higher than other subjects. This reflects the effect of income level on dry weight of food. The METU subjects usually have higher income compared to others. Daily dry diet intake of European countries is about g/day, much higher than our values. This is mostly due to higher meat and meat product intake in European countries. During the last 30 years public health authorities in many countries have started defining the desirable levels of nutrient intake for their population. As a result, both international organizations like FAO, IAEA and WHO and individual countries have established Recommended Dietary Allowance, RDA, and Estimated Safe and Adequate Daily Dietary Intake (ESADDI) values. 2,10 As seen in Table 1, daily dietary zinc intake differs among different population, and for all cases, it is lower than RDA 2 values. According to WHO s 1996 study, estimated dietary requirement of zinc is very much depending on type of food consumed. 11 The amount required maintaining a reserve in body tissues is defined as normative storage requirement. Normative value for zinc is 5.6 mg Zn/d, 9.4 mg Zn/d and 18.7 mg Zn/d for high bioavailabilty, moderate bioavailabilty and low bioavailabilty type diets, respectively. Although zinc concentration of cereals are rather high, they also have high phytate level. 12,13 It is known that phytate is a chelating agent for zinc and other M 2+ type ions. Since bread and other wheat products are by far the most used staple foods, daily dietary intake for average Turkish population should be about 15 mg Zn/d. Also, in the last column of Table 1, %RDA values achieved by the different groups is presented. As expected, it is lower than 100%, changing between 32 87%. It is known that Turkish soil s Se and Zn concentrations are somewhat lower than those of other countries. 14,15 The Canadian RDA for zinc is only 9 mg/day for men, 16 and as explained above the WHO s 12 value is 9.4 mg/day for moderate bioavailable diet. Dietary intakes of Zn in various geographical area in even most western countries are less than 15 mg/day. The conclusion one can draw from this kind of comparison is that there are many population groups with different type of diet, that have lower levels of intake than the RDA, without apparently any significant public health problems so far attributed to Zn deficiency. 10 There was another interesting work carried out in 11 countries on the trace elements in diet, supported by International Atomic Energy Agency (IAEA). During this four year study, , 350 total daily diet samples were analyzed for their zinc, selenium and other trace element content and daily dietary intakes were measured. 6 Turkey was one of 11 countries involved in this study. 4 The average of the 350 measurements was 11.7±5.7 mg Zn/day with median value of These were the actual intake of 350 subjects from 11 countries. In many respects it is more meaningful to compare our results with that of IAEA s. As zinc value is somewhat lower, and RDA value for Zn, which is 15 mg/day, is not attained. In human diet, cereals, onion, garlic and meat represent the main source of selenium. Quantity of selenium within human organism primarily depends on the diet. For example New Zealand citizens contain 3 6 mg of selenium while USA subjects have mg. 17 In most countries, cereal is the main source selenium with up to 50% of the daily intake, meat and fish is about 40% and the dairy product is about 6%. Among cereals, bread has the main contribution. The selenium concentration and daily dietary intake of different population group are given in Table 2. 34

3 Table 1. Daily dietary zinc intake by different population in Turkey Sample* N Dry diet intake, Diet concentration, Intake, RDA, (mg Zn/day) g/day mg Zn/kg mg Zn/day mg/day 100/RDA CHD ± ± ± ± 36 METU ± ± 3 13 ± ± 27 LAL ± ± ± ± 15 W ± ± ± ± 14 S ± ± ± ± 11 FU-F ± ± ± ± 14 FU-M ± ± ± ± 17 * CHD: Children from Ankara University kindergarten, METU: Middle East Technical University members or relatives, LAL: Villagers from Lalahan, near Ankara, W: winter samples, from Ankara University hospital, S: summer samples, from Ankara University hospital, FU-F: Fatih University members or relatives, summer female samples, FU-M: Fatih University members or relatives, summer male samples. Table 2. Daily dietary selenium intake by different population in Turkey Sample* N Dry diet intake, Diet concentration, Intake, RDA, (µg Se/day) g/day µg Se/kg µg Se/day µg/day 100/RDA CHD ± ± ± ± 36 METU ± ± ± LAL ± ± ± W ± ± ± S ± ± ± * CHD: Children from Ankara University kindergarten, METU: Middle East Technical University members or relatives, LAL: Villagers from Lalahan, near Ankara, W: winter samples, from Ankara University hospital, S: summer samples, from Ankara University hospital. Table 3. Zinc and selenium concentrations in various staple foods Sample Description Concentration, Concentration, mg Zn/kg µg Se/kg Wheat Average of four wheat growing regions, collected during ± ± 20 Flour Average of 24 samples from 6 different bakeries in Ankara, 6.0 ± ± 40 collected during summer and winter seasons in 1995 Bread Average of 30 samples from 6 different bakeries in Ankara, 10.0 ± ± 16 collected during summer and winter seasons in 1995 As in the case of zinc, %RDA value achieved is rather low except METU subjects. The average and median selenium daily dietary intake values of IAEA 6 study on 344 subjects are 73±59 µg Se/d and 54 µg Se/d, respectively. This also indicates that our subject s daily dietary intake of selenium is rather low Contribution of bread to daily dietary intake of zinc and selenium The average zinc and selenium concentrations in wheat, flour and bread samples are given in Table 3. WOLNIK 21 investigated 290 American wheat samples and found average zinc concentration as 27 mg/kg, which is higher than Turkish wheat. Also note that average zinc content of flour is less than that of wheat. This is mostly due to the loss of zinc during the milling process during which bran is lost. Since most white bread is made of flour without bran, lower zinc concentration is expected. Wheat products such as flour and bread are major staple food of Turkish people accounted for about 50% of dry diet. 7 Since Zn and Se concentrations of both total diet and bread are known, 6,8 it is possible to calculate percent daily intake of Zn and Se due to bread. 35

4 Table 4. Daily dietary zinc intake from the bread for Fatih University subjects Male subjects (n = 7) Mean Median Range TY-M AM-M MA-M AA-M YS-M SG-M MD-M Daily bread ± intake, g/d Daily Zn intake ± via bread, mg/d Daily dietary ± Zn intake, mg/d % Zn intake ± from bread Female subjects (n = 7) Mean Median Range HA-F FT-F NS-F YU-F SS-F NY-F NG-F Daily bread ± intake, g/d Daily Zn intake ± via bread, mg/d Daily dietary ± Zn intake, mg/d % Zn intake ± from bread Table 5. Daily zinc and selenium intake contributed by bread for AU children Zinc, mg/d Selenium, µg/kg Daily intake via bread 1.1 ± ± 2.0 Daily intake 7.0 ± ± 20 % Intake from bread 17 ± ± 13 In FU-M and FU-F samples, we have measured actual daily intake of bread. Experiments show that the average water content of the bread is 38% and zinc concentration is 10 mg/kg of dry bread. 9 With this information daily zinc intake coming from the bread can be calculated as: Zn coming from bread (mg day) = = Zn in bread (mg/kg) Daily bread consumption (kg) The results for FU-SM and FU-SF subjects are shown in Table 4. It shows that up to 25% of the daily intake of Zn is coming from the bread. Considering the high phytate content of the wheat and wheat products, the bioavailabilty of the Zn will be rather low. We have measured the daily bread consumption of Children of Ankara University Kindergarten (CHD Samples) and calculated the contribution to daily zinc and selenium intake. Daily mean dry bread intake was 108±64 g. Table 5 summarizes zinc and selenium intake due to bread. In this calculation bread zinc and selenium concentrations are taken as 10 mg Zn/kg and 52 µg Se/kg, respectively. As seen, about 20% of the daily dietary intake of these subjects were due to bread. * This work is partially supported by Turkish Scientific and Technical Research Council, TUBITAK, Research Grant TARP-2232, NATO Research Grant No: CRG , IAEA under Research Contract 3575/R3/RB and Turkish Academy of Sciences (TUBA). References 1. W. MERTZ, Trace Elements in Human and Animal Nutrition, Vol. 1, W. MERTZ (Ed.), Academic Press, Recommended Dietary Allowances, National Academy of Science, Washington, DC, T. MUMCU, I. GOKMEN, A. GOKMEN, R. M. PARR, N. K. ARAS, J. Radioanal. Nucl. Chem., 24 (1988) N. K. ARAS, I. OLMEZ, Supplement to Nutrition, 11 (1995) A. O. CAVDAR, E. BABACAN, S. GOZDESOGLU, E. UNAL, J. Trace Elem. Exper. Med., 24 (1997)

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