Reference Range for Zinc Level in Young Healthy Population in Southeast of Iran

Zinc is a micronutrient element, which has an important role in human growth and development. Zinc is a necessary element in the function of many enzymes, cell division, immune system, synthesis of multiple proteins, and DNA and RNA synthesis (1, 2). Zinc plays a major role in infectious diseases (3, 4). Considering the major role of zinc in growth, development, and immune system, daily usage is mandatory (5). High level of Zinc is found in Oysters, Red meat, poultry, beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products. Low level of Zinc is found in vegetable, fruits, tea, coffee, rice, and bread (6). Zinc deficiency usually occurs in negative history of Zinc intake or any zinc-containing supplement intake and is commonly related to nutritional deficiency, but sometimes stems from malignant condition, diabetes mellitus, malabsorption, or other chronic illnesses (7, 8). Zinc deficiency is associated with growth retardation, decreased appetite, abnormal sexual function, abnormal wound healing, immune system dysfunction, neurologic abnormality, and predisposing to diseases such as diarrhea and pneumonia (9, 10). Age, gender, and geographic location have major effects on zinc status (11-14). Reference ranges is defined as 70 - 120 µg/dL, while the values lower than 70 µg/dL is defined as zinc deficiency (15). WHO has reported 800000 deaths per year due to Zinc deficiency (7). Zinc deficiency is known to adversely affect health and immunity; however, excessive quantities of zinc intake may lead to both acute and chronic toxicity (16). Countries vary in the rate at which their populations are exposed to zinc deficiency. The first aim of the present study is to evaluate Zinc status especially in terms of Zinc deficiency in south east of Iran with especial socioeconomic status. The second aim is to respond to this important question "how many populations and whom members need to zinc supplement?".

This cross sectional study was carried out on healthy population in 2011 - 2012 in Zahedan; south east of Iran. The study was approved by ethics committee of Zahedan University of medical sciences. We calculated sample size according to previous studies. Total eligible cases were 320 subjects aged 10 - 30 years. They were selected from 6 postal area of Zahedan city using probability sampling. First, we divided the city into six postal areas. Then, we selected two zones from each area and a maximum of 30 people from each zone. Finally, we selected the subjects randomly from each zone using a list of names.

Inclusion criteria were healthy subjects without heart and liver diseases, gastrointestinal disease, diabetes mellitus, hemolytic anemia, malignancy, opium addiction, smoking, pregnancy, special diet, and supplement consumption during 6 months ago. Informed written consent was obtained from all participants and their parents. Briefly, weight was measured while participants wore light clothes without shoes, using digital scales, and recorded to the nearest 100 g. The height was measured in standing position without shoes, using a tape meter, while the shoulders were in normal state. BMI was calculated as weight (in kilograms) divided by height (in meters) squared. For ages lower than 18 years, Waterlow and Gomez indices were used (17, 18).

A blood sample was taken after 12 to 14 hours of overnight fasting. All blood analyses were stored at -20 degree of centigrade until measurement using graphite furnace atomic absorption spectrometry, Varian, Australia (spectr AA 240fs, 2009, USA) in Razavi hospital of Mashhad University of Medical Sciences. The normal range of serum Zinc level according to this instrument was 70 - 125 µg/dL. In this study, subjects with serum level lower than 70 µg/dL and higher than 125 µg/dL were defined as Zinc deficiency and Zinc excess, respectively.

Statistical analyses were conducted using SPSS 15.0. Continuous variables were presented as mean and standard deviation. An independent sample t-test, ANOVA or Mann-Whitney U-test were used to assess significance of differences for continuous variables. P-values (two-sided) < 0.05 were considered significant.

All 355 cases over 10 years old with healthy condition entered the study. Totally, 320 cases were eligible and evaluated for Zinc status. The age of participants ranged between 10 and 30 years. Mean age was 15.5 ± 2.15 years and median age was 16. About 37.5 % (120 cases) of subjects were male and 62.5% (200 cases) were female. Mean BMI was 21.43 ± 4.15 kg/m² (ranged 13.69 - 33.75 kg/m²). Mean Zinc level was 100.1 ± 16 µg/dL (ranged 62 - 155 µg/dL). In male and female subjects, mean of serum zinc level was 101.46 ± 16.8 µg/dL and 99.13 ± 15.77 µg/dL, respectively (P value = 0.213). In male cases, 1.6% (2 cases) showed zinc deficiency, 89.1% (107 cases) were in normal range, and 9.1% (11 cases) had zinc excess. In female group, 0.5% (1 case) had Zinc deficiency, 94% were in normal range, and 5.5% (11cases) had Zinc excess. Mean zinc status according to BMI was 100.01 ± 16.1 µg/dL with non-significant P-value (0.321). In this study, mean Zinc level did not show significant correlation with age, sex, and BMI (P value > 0.05) (Tables 1 and 2).

This cross sectional study conducted on 320 cases from normal population showed low prevalence (2.1%) of Zinc deficiency; the majority of cases had normal status of zinc, and the minority had zinc excess. literature review for Zinc level in normal population showed that many studies have reported different status for zinc from normal to severe deficiency (19-21).

In study of Hettiarachchi and coworkers (19), the prevalence of Zinc deficiency was much higher than that of our study. In their study in female and male groups, Zinc deficiency was 58.3% and 51.5%, respectively. In another study (20), the prevalence of Zinc deficiency was 38.2% with similar sex prevalence. In a study carried out in southwest of Iran (21), the prevalence of Zinc deficiency was higher than that of the present study, so that serum Zinc level was 68.4-205 µg/dl with the mean value of 103.60 µg/dL. Zinc deficiency rate in males and females was 57.7% and 57.4%, respectively. These values were not significantly different. Age, sex, and BMI did not show significant relationships with the prevalence rate.

In our study, the mean serum zinc in males was higher than females without a significant difference, which is in agreement with the results of other studies (21-24). Only 2 studies reported higher mean zinc concentrations in female than male cases (25, 26). In other study, the prevalence of zinc deficiency was 31% (27). In study of Hashemi and coworkers, the prevalence of Zinc deficiency was 47.1% (24). In another study on female cases, the incidence of Zinc deficiency was reported as 7.1% (28). Dehghani (29) and coworkers reported the prevalence of zinc deficiency much lower than the prevalence reported in other studies, although in comparison with our study, they revealed much more prevalence rate for zinc deficiency. In Dehghani et al. study, mean zinc level was 122.3 ± 55 µg/dL. Zinc status did not show statistical relation to BMI, sex, and age. Study of prevalence of Zinc deficiency in other parts of Iran has revealed different rates such as 28%, 30.1%, and 85.5% (27, 30, 31). One of the main reasons for different reported rates in all around the world may be related to zinc concentration in soil. Excessive supplement therapy, diet, and various cut-of point of zinc level could be other possible reasons. Consumption of large amount of phytate has had a relationship with high prevalence of zinc deficiency (32).