Worrying trends in salt intake in China

Monique Tan

PhD Student, Queen Mary University of London

Why does salt matter in China?

Considered “king of all flavours”, salt has played an essential role in the preparation and preservation of foods for thousands of years in China. However, eating too much salt increases the risk of multiple health conditions, especially cardiovascular disease (via raised blood pressure), which now accounts for 40% of deaths in China [1].

The problem is that most estimates of salt intake in China lack accuracy, due to unreliable methods of assessment. The most accurate way to measure salt intake is to collect the urinary excretion of sodium over 24 hours. While this has been collected in China, the data has never been comprehensively reviewed.

Robust estimates of salt intake in China are necessary in order to best inform the development of tailored strategies to reduce people’s salt intake. An example of a promising strategy for China is the replacement of regular salt with potassium salt, which contains less sodium (which raises blood pressure) and more potassium (which lowers blood pressure).

A systematic search for all available data

We searched both English and Chinese language databases for all studies ever published that reported 24-hour urinary excretion of either sodium or potassium in China. We found a total of 70 studies (involving 26,767 participants) reporting sodium data, of which 59 (representing 24,738 participants) also reported potassium data. The data spanned four decades and covered most provinces of China. Compared to previous reviews of salt intake in China (which were not systematic), our review is by far the largest.

Findings: extremely high salt intakes at all ages, a persisting North-South divide, and consistently low potassium intakes

Pooling all this data together using a meta-analysis allowed us to reveal important patterns in salt and potassium consumption in China:

  • Children and adolescents already exceed the limit set for adults: The World Health Organization (WHO) sets the maximum limit for salt intake at 5 grams per day for adults, and recommends adjusting this limit downwards for children and adolescents according to their energy requirements [2]. In China however, children aged 3-6 already consume 5 grams of salt per day. The WHO limit was far exceeded by children and adolescents aged 6-16, whose salt intake averaged a worrying 8.7 grams of salt per day. In adults, average salt intake was 10.9 grams per day, which is more than double the WHO-recommended limit, and is one of the highest salt intake in the world. Of the countries where 24-hour urinary sodium has been collected, China had the highest salt intake.

bar graph 2019.07.04

Note: Salt intake calculated from the 24-h urinary sodium excretion with a conversion factor of 2.5 (1 g of sodium = 2.5 g of salt), without correcting for non-urinary losses of sodium.

  • Opposite trends between North and South China: The impact of different climates and traditions is still visible today in China’s regional cuisine, with a predominance of wheat in the North and rice in the South. The high-wheat diet in northern China also includes nuts, fruits, eggs, milk, and in more recent years, instant noodles, frozen dumplings, and more Western-type foods. Although such a diet is increasingly seen in the more urbanised areas of southern China, the traditional southern diet still prevails, with rice, vegetables, meat, poultry, and fish [3].Interestingly, salt intake in northern China has declined over the past 40 years which may be the result of both efforts by the government to increase awareness of salt and less reliance on pickles, owing to a greater year-round availability of vegetables. Despite the decline, the average salt intake in northern Chinese adults remains high, at 11.2 grams per day, still more than double the WHO-recommended limit. In contrast, salt intake in southern China has actually increased over the same time period. This could be due to a growing reliance on processed foods and out-of-home meals – typically high in salt – which has overpowered government efforts to increase awareness of salt.bubble plot 2019.07.04
  • Potassium intake was less than half the recommended levels: While salt intake is far too high, potassium intake has been consistently low throughout China for the past four decades, with individuals of all age groups consuming less than half the recommended minimum intakes [4, 5].

Urgent need to speed up salt reduction and increase potassium intake

As much as a fifth of the world’s population lives in China. Achieving salt reduction together with increasing potassium intake across the country would result in an enormous benefit for global health. Based on our findings, the following actions needs to be taken:

  • Replace regular salt with potassium salt: In China, most of the salt consumed still comes from the salt added by the consumers themselves or by food handlers, while cooking or from salty sauces. This contrasts with Western countries, where most salt comes from processed foods. This means that in China, behaviour change remains imperative to reduce sodium intake. An easy way for the general population to achieve this is to replace their regular salt with potassium salt, which can be used in the same way. This would also have the additional benefit of increasing their potassium intake, which is currently too low.
  • Start early: Childhood and adolescence are key periods in the formation of dietary habits and taste preferences. High blood pressure in childhood tracks into adulthood, leading to cardiovascular disease. If a child eats more salt, they will develop the taste for salt and are more likely to eat more salt as an adult, and to have higher blood pressure.
  • Anticipate new contributors to salt intake: The rapid increase in the consumption of processed foods and of food from street markets, restaurants, and fast food chains must be addressed, before the hard-won declines in salt intake are offset. This can be done by setting maximum targets for the salt content of foods, and substituting regular salt with potassium salt. Targets should be set for processed foods sold in retail stores, but also for out-of-home processed foods sold in quick service restaurants, takeaway, and meal delivery businesses. This is crucial to create a level playing field where salt is reduced across the board, helping to guide the population in becoming accustomed to a less salty taste.

Tan M, He FJ, Wang C, et al. Twenty-Four-Hour Urinary Sodium and Potassium Excretion in China: A Systematic Review and Meta-Analysis. J Am Heart Assoc. Epub ahead of print 2019. DOI: 10.1161/JAHA.119.012923

References

[1]        Zhao D, Liu J, Wang M, et al. Epidemiology of cardiovascular disease in China: current features and implications. Nat Rev Cardiol 2019; 16: 203–212.

[2]        World Health Organization. Guideline: sodium intake for adults and children. Geneva: World Health Organization, Department of Nutrition for Health and Development, 2012.

[3]        Batis C, Sotres-Alvarez D, Gordon-Larsen P, et al. Longitudinal Analysis of Dietary Patterns in Chinese Adults from 1991 to 2009. Br J Nutr 2014; 111: 1441–1451.

[4]        World Health Organization. Guideline: potassium intake for adults and children. Geneva: World Health Organization, Department of Nutrition for Health and Development, 2012.

[5]        Chinese Nutrition Society. Chinese Dietary Reference Intakes (2013 edition) [M]. Beijing: Science Press, 2014.

 

“This piece was originally published on The Conversation

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