Salt intake in China is confirmed to be among the highest in the world, with adults over the past four decades consistently consuming on average above 10g of salt a day, which is more than twice the recommended limit, according to new research led by Queen Mary University of London.
The systematic review and meta-analysis, funded by the National Institute for Health Research and published in the Journal of the American Heart Association, also found that Chinese children aged 3-6 are eating the maximum amount of salt recommended by the World Health Organization for adults (5g a day) while older children eat almost 9g/day.
Excess salt intake raises blood pressure, a major cause of strokes and heart disease, which accounts for approximately 40 per cent of deaths in the Chinese population.
The team reviewed all data ever published on salt intake in China (which involved about 900 children and 26,000 adults across the country) and found that salt intake has been consistently high over the past four decades, with a North-South divide.
While salt intake in northern China is among the highest in the world (11.2g a day) it has been declining since the 1980s when it was 12.8g a day, and most markedly since the 2000s.
This could be the result of both governmental efforts in salt awareness education and the lessened reliance on pickled food – owing to a greater year-round availability of vegetables.
However, this trend of decrease was not seen in southern China, which has vastly increased from 8.8g a day in the 1980s to 10.2g a day in the 2010s.
This could be due to governmental efforts being mitigated by the growing consumption of processed foods and out-of-home meals.
These latest results contradict those of previous studies based on less robust data which reported declines in salt intake across the country.
Potassium, which is naturally found in fruits and vegetables, and is in potassium salt, has the opposite effect of sodium (salt) on blood pressure: while sodium increases blood pressure, potassium lowers it.
The researchers reviewed potassium intake and found that in contrast to salt intake, it 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.
Lead author Monique Tan from Queen Mary University of London said: “Urgent action is needed in China to speed up salt reduction and increase potassium intake.
High blood pressure in childhood tracks into adulthood, leading to cardiovascular disease.
If you eat more salt whilst you are young, you are more likely to eat more salt as an adult, and to have higher blood pressure.
These incredibly high salt, and low potassium, figures are deeply concerning for the future health of the Chinese population.”
Feng J He, Professor of Global Health Research at Queen Mary University of London and Deputy Director of Action on Salt China, added:
“Salt intake in northern China declined, but is still over double the maximum intake recommended by the WHO, while salt intake actually increased in southern China.
Most of the salt consumed in China comes from the salt added by the consumers themselves while cooking.
However, there is now a rapid increase in the consumption of processed foods and of food from street markets, restaurants, and fast food chains, and this must be addressed before the hard-won declines are offset.”
Graham MacGregor, Professor of Cardiovascular Medicine at Queen Mary University of London and Director of Action on Salt China said: “A coherent, workable, and nationwide strategy is urgently needed in China.
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.”
The trends found in this latest study partially contradict those of earlier studies which found large declines of salt intake across the whole of China.
The researchers say these latest results are far more robust than the previous estimates which have relied on surveys of people’s dietary habits.
The team instead determined salt intake exclusively with the use of data from urine samples taken over a 24 hour period.
Salt intake assessed by dietary methods is unreliable because most of the salt in the Chinese diet comes from the salt added during home cooking or in sauces, which is highly variable and difficult to quantify.
Furthermore, processed and out-of-home foods are increasingly consumed but their salt content tends to be inaccurately reported in food composition tables.
Excessive dietary salt (sodium chloride) intake is associated with an increased risk for hypertension, which in turn is especially a major risk factor for stroke and other cardiovascular pathologies, but also kidney diseases.
Besides, high salt intake or preference for salty food is discussed to be positive associated with stomach cancer, and according to recent studies probably also obesity risk.
On the other hand a reduction of dietary salt intake leads to a considerable reduction in blood pressure, especially in hypertensive patients but to a lesser extent also in normotensives as several meta-analyses of interventional studies have shown.
Various mechanisms for salt-dependent hypertension have been put forward including volume expansion, modified renal functions and disorders in sodium balance, impaired reaction of the renin-angiotensin-aldosterone-system and the associated receptors, central stimulation of the activity of the sympathetic nervous system, and possibly also inflammatory processes.
Not every person reacts to changes in dietary salt intake with alterations in blood pressure, dividing people in salt sensitive and insensitive groups.
It is estimated that about 50-60 % of hypertensives are salt sensitive.
In addition to genetic polymorphisms, salt sensitivity is increased in aging, in black people, and in persons with metabolic syndrome or obesity. However, although mechanisms of salt-dependent hypertensive effects are increasingly known, more research on measurement, storage and kinetics of sodium, on physiological properties, and genetic determinants of salt sensitivity are necessary to harden the basis for salt reduction recommendations.
Currently estimated dietary intake of salt is about 9-12 g per day in most countries of the world.
These amounts are significantly above the WHO recommended level of less than 5 g salt per day.
According to recent research results a moderate reduction of daily salt intake from current intakes to 5-6 g can reduce morbidity rates.
Potential risks of salt reduction, like suboptimal iodine supply, are limited and manageable.
Concomitant to salt reduction, potassium intake by higher intake of fruits and vegetables should be optimised, since several studies have provided evidence that potassium rich diets or interventions with potassium can lower blood pressure, especially in hypertensives.
In addition to dietary assessment the gold standard for measuring salt intake is the analysis of sodium excretion in the 24 h urine.
Spot urine samples are appropriate alternatives for monitoring sodium intake. A weakness of dietary evaluations is that the salt content of many foods is not precisely known and information in nutrient databases are limited.
A certain limitation of the urine assessment is that dietary sources contributing to salt intake cannot be identified.Salt reduction strategies include nutritional education, improving environmental conditions (by product reformulation and optimization of communal catering) up to mandatory nutrition labeling and regulated nutrition/health claims, as well as legislated changes in the form of taxation.
Regarding dietary interventions for the reduction of blood pressure the Dietary Approaches to Stop Hypertension (DASH) diet can be recommended.
In addition, body weight should be normalized in overweight and obese people (BMI less than 25 kg/m2), salt intake should not exceed 5 g/day according to WHO recommendations (<2 g sodium/day), no more than 1.5 g sodium/d in blacks, middle- and older-aged persons, and individuals with hypertension, diabetes, or chronic kidney disease, intake of potassium (~4.7 g/day) should be increased and alcohol consumption limited.
In addition, regular physical activity (endurance, dynamic resistance, and isometric resistance training) is very important.
Are “natural” salts healthier than table salt?
Salt is harvested from salt mines or by evaporating ocean water. All types of salt are made of sodium chloride, and the nutrient content varies minimally. Although less processed salts contain small amounts of minerals, the amount is not enough to offer substantial nutritional benefit. Different salts are chosen mainly for flavor.
The most widely used, table salt, is extracted from underground salt deposits. It is heavily processed to remove impurities, which may also remove trace minerals. It is then ground very fine. Iodine, a trace mineral, was added to salt in 1924 to prevent goiter and hypothyroidism, medical conditions caused by iodine deficiency. Table salt also often contains an anticaking agent such as calcium silicate to prevent clumps from forming.
Kosher salt is a coarsely grained salt named for its use in traditional Kosher food preparation. Kosher salt does not typically contain iodine but may have an anti-caking agent.
Sea salt is produced by evaporating ocean or sea water. It is also composed mostly of sodium chloride, but sometimes contains small amounts of minerals like potassium, zinc, and iron depending on where it was harvested. Because it is not highly refined and ground like table salt, it may appear courser and darker with an uneven color, indicating the remaining impurities and nutrients. Unfortunately, some of these impurities can contain metals found in the ocean, like lead. The coarseness and granule size will vary by brand.
Himalayan pink salt is harvested from mines in Pakistan. Its pink hue comes from small amounts of iron oxide. Similar to sea salt, it is less processed and refined and therefore the crystals appear larger and contain small amounts of minerals including iron, calcium, potassium, and magnesium.
Larger, courser salt granules do not dissolve as easily or evenly in cooking, but offer a burst of flavor. They are best used sprinkled onto meats and vegetables before cooking or immediately after.
They should not be used in baking recipes.
Keep in mind that measurements of different salts are not always interchangeable in recipes.
Generally, sea salt and table salt can be interchanged if the granule size is similar. However, table salt tends to have more concentrated, saltier flavor than kosher salt, so the substitution is one teaspoon of table salt for about 1.5 to 2 teaspoons of kosher salt depending on the brand.
More information: Monique Tan et al, Twenty‐Four‐Hour Urinary Sodium and Potassium Excretion in China: A Systematic Review and Meta‐Analysis, Journal of the American Heart Association (2019). DOI: 10.1161/JAHA.119.012923
Journal information: Journal of the American Heart Association
Provided by Queen Mary, University of London