Background

Sodium is an essential mineral needed by the human body that must be obtained from food. The role of sodium is to maintain electrolyte and water balance in the human body. It is also important in nerve and muscle function [1]. However, high consumption of sodium can lead to non-communicable diseases (NCDs) especially cardiovascular disease [2]. A recent study also suggests that salt or sodium intake is a potential risk factor for obesity, another major concern in public health [3].

In Malaysia, the prevalence rates of diseases associated with high sodium intake are high. For example, the overall prevalence of hypertension (known and undiagnosed) among adults of 18 years and above in Malaysia in 2015 was 30.3%. Meanwhile, the prevalence of obesity in the same age group was 17.7% [4]. There is no sign of decline in these diseases which prompts an urgent need to find comprehensive and effective prevention strategies.

Based on compelling evidence, the best strategy to help prevent diseases related to high sodium consumption is to limit dietary intake of sodium [5]. The World Health Organization (WHO) recommends a reduction to below 90 mmol (< 5 g salt) per day or < 2000 mg/day sodium in the adult general population [6]. The Recommended Nutrient Intake (RNI) 2017 for Malaysia suggests a sodium requirement of 1500 mg/day for adults 19 years and above [7].

By knowing the sodium requirement and foods with high in sodium, the individual can easily plan for their daily food intake by avoiding high-sodium foods. At the same time, the public health sector or related agencies can plan for effective intervention by understanding the pattern of high sodium food consumption in the population. Therefore, this study aims to provide baseline information on high sodium food consumption patterns in the Malaysian population.

Methods

Study design and study population

Data were taken from the Malaysian Community Salt Survey (MyCoSS), a nationwide cross-sectional study conducted between October 2017 and March 2018. The target population was respondents resided in the non-institutional living quarters. Those staying in institutional residents such as hotel, hostels, hospitals, and prisons were excluded from the survey. Pregnant women, those who began diuretic therapy in the last 2 weeks, having kidney disease and any condition that limit their ability to collect 24-h urine were also excluded from this study. Ethical approval was obtained from the Medical Research Ethics Committee (MREC), Ministry of Health, and Queen Mary (University of London) Research Ethics Committee, UK. Signed informed consent form was obtained from each respondent before the interview and collection of urine samples.

Sample size

The sample size was calculated using a formula for estimating population prevalence. Sampling was designed to cover both urban and rural areas for every state in Malaysia. Calculations were done on all objectives as listed, and the biggest sample size was on the knowledge on the effect of high salt on health. We applied the findings of the previous salt study among the health workers in Malaysia (MySalt 2015) [8]. With the prevalence on knowledge on the effect of high salt on health of 6%, confidence level of 95%, estimated design effect of 1.5, the optimum sample size for a stratum was 520 respondents. The sample size was then inflated 25% to cover for non-responses; hence, the sample size for each stratum was 650 respondents, estimated sample size was 1300 respondents.

Food frequency questionnaire (FFQ)

The Food Frequency Questionnaire (FFQ) consisting of 104 food items in 11 food groups was used to gain information on high sodium food consumption pattern. This FFQ has been used in the Malaysian Adult Nutrition Survey (MANS) 2014 with some modification and selection of high sodium food by the expert in nutrition [9]. Ten experts in nutrition applied several findings and discussed before finalizing all 104 food items to include in this FFQ. Respondents were asked in detail about each food item in a face-to-face interview by trained research assistants. Respondents answered all 104 food items in terms of frequency of intake either on a daily, weekly, or monthly basis and the number of servings they consumed during each time they ate the food. If the respondent did not consume the food on a monthly basis, they answered “0” in the per/month column.

Data analysis

The data were analyzed using IBM SPSS version 23 for Windows (SPSS Inc., Chicago, IL, USA). Sample weight was calculated by determining the base or design weight and adjusted for study non-responses. The sampled unit weight represented the probability of it being selected into the sample. The final weight used in the analysis was the post-stratification weight referring to the existing Malaysian population information provided by DOSM. Since this study applied a complex sampling design, the analysis was conducted accordingly with 95% confidence interval. For FFQ, the conversion of food frequency to the amount of sodium in food intake was carried out using the following formula:

Amount of sodium (g) per day = frequency of intake (convert per day) × serving size × total number of servings × weight (in gram) of food in one serving × amount of sodium in 1 g of the food.

Descriptive statistics were used for describing the characteristics of the respondent and patterns of high sodium food consumption.

Results

A total of 1047 respondents were involved in this study making a response rate of 80.5%. About 1032 respondents (98.6%) completed the FFQ. Majority respondents aged 55 to 64 years old and there were more women (59.1%) involved in this study compared to men (40.9%). More respondents were from rural areas (58.5%) compared to urban areas (41.5%) (Table 1). About 54.1% of adults were found to exceed the sodium intake recommendation of <2000 mg/day by FFQ assessment. Our study also found that fried vegetables, white/wholemeal bread and omelet were the most preferred high sodium food which was consumed by more than 80% of the Malaysian population as shown in Table 2. These top three foods remain in their rank when the analysis focused on the strata level (Table 3) and sex (Table 4). There was a difference in the urban area when white/wholemeal bread took the first position, the same as in male (Tables 3 and 4).

Table 1 Sociodemographic characteristics of respondent (N = 1032 respondents)
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Table 2 Top 10 high sodium food most consumed by Malaysian adults (N = 1032 respondents)
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Table 3 Top 10 high sodium food most consumed by Malaysian adults by strata
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Table 4 Top 10 high sodium food most consumed by Malaysian adults by sex
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Mee kolok or kampua mee and light soy sauce contributed the highest sodium consumption in individuals with median consumption of 256.5 mg/day and 248.1 mg/day respectively. However, the percentage of individuals who consumed these two food items was only 9.0% and 33.2%, respectively (Table 5). Those who consumed ≥2000 mg sodium per day were found to have a higher intake of fried vegetable, roti canai/roti telur, omelet, fried rice, and chicken curry compared to those who consumed less than 2000 mg sodium per day according to 24-h urinary sodium analysis (Table 6).

Table 5 Top 10 food sources (food item) with the highest sodium consumption among Malaysian adults
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Table 6 Top 10 food consumption by high sodium intake of ≥2000 mg/day sodium and less than <2000 mg/day sodium
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Discussion

This nationwide survey showed that the top five high sodium foods most frequently consumed by Malaysian adults were fried vegetables, white bread/wholemeal bread, omelet, fried chicken with spices and fried rice. Generally, the most popular fried vegetables in Malaysia is stir-fried like spinach [10]. The findings are almost similar to national data on food consumption statistics among Malaysians, where about 80% of the Malaysian adults reported to consume white bread/wholemeal bread [11]. However, as the study focused on high sodium food, further comparisons cannot be done with Malaysian food consumption statistics database.

Prepared or home cooked food, such as fried vegetable, omelet, fried chicken, and fried rice, are believed to contribute the highest sodium intake in Malaysia based on the high prevalence of consumption. Data from the International Study of Macro-and Micro-Nutrients (INTERMAP) study in China found that most dietary sodium came from salt added during preparing or cooking [12]. The same study reported that in developed countries, such as Japan, UK, and USA, most of the sodium came from processed foods.

The pattern of food preference was almost similar in urban or rural area and in men or women. However, in urban area and in men, white/wholemeal bread was more preferred compared to fried vegetables. A review paper from the Dublin Institute of Technology regarding food consumption trends and drivers also reported that urbanization was the main factor or drive to the high intake of processed food such as bread [13]. A cross-sectional study among 300 Malaysian university students also showed similar findings when men tend to consume more industrial processed food that was high in sodium, compared to women who mainly obtained sodium from prepared food [14].

The concern was on the consumption of roti canai/roti telur (flatbread) and fried noodles in men due to the high prevalence and high sodium from these foods. Rather than as a source of sodium, roti canai also contained high amount of fat from its main ingredient of margarine, and it was also cooked with cooking oil [15]. A cross-sectional study in Malaysia also found overweight adults consumed more roti canai and fried noodles compared to their normal weight counterpart [16].

Kolok mee or kampua mee and light soy sauce appeared as the food most contributed to sodium consumption. Light soy sauce contributed the main source of sodium in food, as it was used as a condiment in most food preparation, including in mee kolok or kampua mee. There was a global overview of national programs to encourage food industries to reduce sodium in their products. The document also emphasized that products contributing to salt or sodium in the diet usually include sauces, particularly soy sauce and fish sauce in many Asian countries [17]. A local survey among university students also reported that majority of the students added salt/soy sauce to food and dipped food in soy sauce mixed with chopped chilies/garlic and/or sambal belacan [14].

Looking into those who consumed more or equal to 2000 mg sodium per day, the preferred food is quite similar to the respondents who consumed sodium less than 2000 mg per day. However, the quantity of intake played a major role. Respondents who consumed sodium more than 2000 mg sodium per day ate large portions of fried vegetable, roti canai/roti telur, omelet, fried rice, and chicken curry compared to those who consumed less than 2000 mg sodium. Personal initiative to cut off the quantity or portion of high sodium food that they consumed can be the best strategy to reduce sodium intake individually. However, in a community approach, reduction in salt intake can be achieved by a gradual and sustained reduction in the amount of sodium added to foods by the food industries [18, 19].

Conclusion

There are several aspects to highlight when describing patterns of high sodium food consumption among Malaysian adults. First, is the high sodium food choice, where almost similar food items were in the list of top ten. Second, is the method of preparation when most Malaysian adults obtained sodium from cooking or preparation of food. Third, is the amount of food consumed where it directly influence the sodium consumption. Therefore, an effective campaign targeting individual approach, community and also food industry is needed to prevent excessive sodium intake that linked to increased risk of hypertension and cardiovascular diseases.