Selenium content in selected foods from the Saudi Arabia market and estimation of the daily intake

1 Introduction

The trace mineral selenium (Se) is an essential nutrient of fundamental importance to human health, but it is required only in small amounts (Thomson, 2004). Selenium is also toxic and, therefore, could cause selenium poisoning in humans and animals when intake exceeds the safe and adequate level (Hartikainen, 2005). Selenium is incorporated into proteins to make selenoproteins (Fragra, 2005), and several selenoproteins defend against oxidative stress (Goldhaber, 2003). Selenium deficiency can lead to heart disease, hypothyroidism and a weakened immune system (Combs, 2000; Ellis and Salt, 2003). Keshan disease and Kashin–Beck disease were found in China where the selenium content was very low in the soil (Cheng and Qian, 1990; Yang et al., 1993), while selenium has toxic effects in high amounts (Pappa et al., 2006). Chronic toxicity of selenium in humans results in selenosis, characterized by hair loss and nail brittleness, gastrointestinal problems, skin rash, ‘‘garlic-breath” odor and nervous system abnormalities (Yang et al., 1983; Yang and Zhou, 1994).

The dietary intake of selenium depends on its concentration in food and the amount of food consumed (Pappa et al., 2006). The selenium content of food varies depending on the content of the element in the soil where the animal was raised or the plant was grown (IOM, 1998; Uden et al., 2004; Barclay et al., 1995). Food is the main source of selenium for humans. In particular, meat and seafood are key sources, because animals require selenium, unlike plants (Klapec et al., 2004; Sirichakwal et al., 2005). The dietary intake of selenium varies considerably across populations around the world because of the large variability of the selenium content of foods (McNaughton and Marks, 2002). Therefore, it is necessary to monitor the selenium content in representative and widely consumed foods in each country.

Precise determination of selenium content in the food is quite important because there is a narrow margin of safety between adequate amount and overconsumption. To analyze trace selenium, there are various methods currently available (Foster and Sumar, 1995) including neutron activation analysis (Slejkovec et al., 2000), atomic fluorescence spectrometry (Pappa et al., 2006; Semenova et al., 2003; Tinggi et al., 1992), atomic absorption spectrometry (AAS) using either electrothermal atomization (Hussein and Bruggeman, 1999) or hydride generation method (Tinggi et al., 1992; Mindak and Dolan, 1999), and inductively coupled plasma spectrometry (ICP) (Kim et al., 1990; Masson et al., 2005; Featherstone et al., 2004) and ICP/mass spectrometry (MS) (Park and Kim, 2001). For this study, ICP–MS for the analysis of selenium has been optimized and applied because of the low detection limit and high efficiency.

In spite of many concerns about selenium intake, the data for the selenium in foods is very limited in Kingdom of Saudi Arabia. Therefore this study was carried out to produce a finite food selenium and to assess the dietary intake of selenium for the Saudi Arabian population in a limited manner based on the data from the food balance sheet of KSA given by Food and Agriculture Organization (FAO) and from questionnaire.

2 Experimental

3 Results

The number of selected food items in each food group was as follows: cereals and cereals products (n = 8), legumes (n = 6), leafy vegetables (n = 8), non-leafy vegetables (n = 9), tubers (n = 3), fruits (n = 12), meats (n = 5), eggs (n = 1), fats and oils (n = 4), milk and products dairy (n = 6) and nuts (n = 6).

An analytical quality assurance test was performed. Then, the results obtained were compared with the results obtained from the standard reference material and they were satisfactory (recovery: 101.5%). The instrumental quantitative detection limit of selenium was 0.3 ng. Selenium content in various foods is shown in Table 1. The highest values were found in meats (0.216–0.658 μg/g), eggs (0.226 μg/g), and cereals and cereals products (0.043–0.165 μg/g). Legumes (0.220–0.045 μg/g), fruits (0.004–0.032 μg/g), vegetables (0.001–0.067 μg/g), tubers (0.001–0002 μg/g), fats and oils (0.002–0.007 μg/g), milk and dairy products (0.024–0.039 μg/g) and nuts (0.015–0.145 μg/g) contained very low levels of selenium.

Considering the amount of food consumed, the major food sources of selenium intake for Saudi were cereals and cereals products (30.2%), legumes (24.7%), meats (20.3%), milk and dairy products (9.2%), eggs (6.9%), non-leafy vegetables (3.4%), leafy vegetables (2.8%), Fruits (1.2%), tubers (0.5%), fats and oils (0.5%) and nuts (0.3%) as shown in (Fig. 1). The selenium intake of the Saudi Arabia population was estimated by multiplying the mean intake of each food item by the selenium content in each food.

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Figure 1

The contribution of food group on selenium intake of Saudi Arabian (% of total estimated selenium intake).

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As a result, the estimated selenium intake of Saudi Arabia was 121.65 μg/person/day by using food balance sheet of KSA FAO (1994–1996) The results which are shown in Table 2 reflect the Se daily intake according to the food balance of KSA shown by FAO and 75.00 μg/person/day by using questionnaire data as shown in Table 3. Results obtained were similar to the values reported for Netherlands, Japan, China, USA and Australia as seen in Table 4 which shows the estimated amounts of daily dietary selenium intakes in other countries.

4 Discussion

The food and nutrition database is quite important for an accurate evaluation of nutrient intake from dietary intake surveys. Therefore, the selenium content database of the foods frequently consumed by Saudi people was developed for the estimation of selenium intake by them. Most animal foods such as fish, meats, and eggs have a high selenium content, which has previously been reported (Sirichakwal et al., 2005). On the other hand, vegetables and fruits are assumed to contain very low level of selenium unlike foods of animal origin, because selenium is not an essential element for the growth of plants as it is for animals (Klapec et al., 2004). Our data are similar to those of an Australian study, which reported selenium levels of 0.63 μg/g in fish and 0.38 μg/g in meats (McNaughton and Marks, 2002). Also similar to the reported study by Korean, which reported selenium levels of 0.448–0.788 μg/g in fish, 0.169–0.324 μg/g in meats, 0.267 μg/g in eggs, 0.043–0.216 μg/g in cereals, 0.006–0.052 μg/g in vegetables, 0.003–0.028 μg/g in fruits, 0.008 μg/g in fats and oils and 0.013–0.146 μg/g in nuts (Choi et al., 2009).

According to the database of the United States Department of Agriculture National Nutrient, foods with the high content of selenium are Brazil nuts (19.2 μg/g), wheat flour (0.71 μg/g) and barley (0.38 μg/g). Due to the presence of many types of food with higher selenium content in the United States than in Saudi Arabia, the selenium intake of the Americans is considered higher than that of Saudi Arabia. Recently, efforts have been made to increase the selenium content of plants by adding selenium to the soil; selenium-fortified food products can be found on Saudi Arabia markets.

In this study it was found that, the major food source of selenium intake in the Saudi Arabia diet was cereals and cereals products (30.2%) followed by legumes (24.7%) and meats (20.3%) (Fig. 1), because these groups are consumed in a very large amount by the Saudi.

Other studies have also reported that the major contributors to selenium intake are cereals and bakery products followed by fish and shellfish, meats and meat products, and dairy products (Gonzalez et al., 2006). Moreover, it has been pointed out in some reports that the heavy metals in fish interact with selenium, resulting in low bioavailability (Robinson and Tomson, 1983). Therefore, further study is necessary to consider the bioavailability of selenium in foods to correctly determine the bioavailable selenium intake value.

The estimated selenium intake of Saudi in this study was 75–122 μg/person/day, and this level was quite close to the recommended intake (72 μg/person/day, Van Dokkum et al., 1989), and 58–85 μg/person/day (Food Standards Australia and Zealand, 2003). More detailed estimation of selenium intake by merging selenium content data with individuals’ food intake data would be necessary to develop a nutrition program tailored for the particular needs of specific group. This was not attempted because it goes beyond the scope of this study.

Comparing to the cases of other countries, the selenium intake of Saudi falls in the middle of ranges reported and is considerably lower than that of the Canadian and Japanese and higher than Greece, Korea, UK, Egypt, Italy and Sweden (Table 4). Before comparing the intake levels among different countries, it is necessary to reach a consensus on the issues such as standard principles or criteria for matching of food items of different countries.

5 Conclusions

By analyzing the selenium content in representative food items in Saudi Arabia, a selenium database was made on a limited scale. The food balance sheet of KSA given by Food and Agriculture Organization (FAO) were utilized to select foods for analysis. Wheat, meat and vegetables turned out to be the major sources of selenium for Saudi.