Salt is the first of all flavors, and the poet Li Bai once praised: "When the guest arrives, he knows to stay drunk, and there is only crystal salt on the plate."
For millions of years, the only source of salt for human ancestors was naturally occurring salt in food, with a salt intake of less than 0.5 g/day [1]. About 5,000 years ago, with the discovery of salt's antiseptic properties, salt gradually became the most taxed and traded commodity in the world. Currently, although refrigeration technology has eliminated the need for salt as a preservative, the current average salt intake in most countries is around 10 g/d [2], and from evolutionary time scales, human salt intake has increased more than 20-fold in a short period of time.
Eating salt is no trivial matter, and the impact of high salt intake on our health is multifaceted, but there is no suitable mechanism for human physiology to excrete large amounts of salt.
In 2017, high salt intake took a huge burden worldwide, with about 70 million disability-adjusted life years and 3 million deaths, and the probability of further inducing related diseases is even higher if you have a chronic disease such as hypertension. High salt intake is the number one risk factor in the diet and is one of the top three dietary risk factors worldwide [3]. At present, the salt intake of mainland residents is still at a high level, about 11 g/d for adults, which is more than twice the recommended upper limit (5 g/d) of the World Health Organization and the Dietary Guidelines for Chinese Residents (2022).
What is salt? Just teach it to be with sodium.
Salt and sodium have a quantitative relationship (1 g of sodium = 2.5 g of salt), and salt contains 40% sodium and 60% chloride by weight. Salt is the main source of dietary sodium (about 90%). "Sodium" is commonly used in scientific publications and on food labels, and we can calculate the salt content of foods according to a 1:2.5 conversion relationship [4].
Studies have found that high salt intake is closely related to damage to key organs.
Heart: High salt intake is associated with the occurrence of hypertension, especially hypertension with age, resulting in heart damage including myocardial fibrosis, left ventricular diastolic dysfunction, left ventricular hypertrophy, etc., which can lead to ischemic heart disease, hypertensive heart disease and heart failure.
Brain: High salt intake can cause cognitive dysfunction, white matter damage, cerebral hemorrhage, and cerebral infarction, which is closely related to stroke and senile dementia, and reducing salt intake in the diet will help reduce the risk of headaches.
Kidneys: High salt intake can cause increased proteinuria, renal hemodynamic abnormalities, decreased glomerular filtration rate (renal function), and renal fibrosis, leading to chronic kidney disease and accelerating the progression of kidney disease.
Gastric cancer: High salt intake increases the risk of Helicobacter pylori infection, which is an important risk factor for gastric cancer.
Osteoporosis: High salt intake can lead to changes in bone mineral and density, leading to osteoporosis and kidney stones.
Overweight and obesity: High salt intake pierces fat accumulation and is associated with overweight and obesity, and overweight obesity can induce a variety of metabolic diseases.
Salt promotes organ damage through a variety of pathways. Factors have been identified as persistent elevation of blood pressure, vascular damage, hormones, inflammation, immune response, gastric mucosal injury, gut microbiota, urinary calcium excretion, abnormal body fat metabolism, and fluid consumption [4], and these complex factors are also interrelated.
The situation of salt reduction is urgent, and it is necessary to limit the amount of "salt".
The incidence of hypertension in the mainland is higher in the north than in the south, and the large intake of salt in the daily diet of northerners is an important reason. Patients with kidney disease should minimize salt intake, with 1 kg of water sodium retention increasing for every 0.5 g of sodium. For patients with pre-existing conditions, it is best not to consume more than 3 g of salt per day.
Cost-benefit analyses have shown that universal salt reduction is highly cost-effective and cost-effective in reducing cardiovascular disease and premature mortality [5]. The UK's salt reduction programme prevents around 9,000 cardiovascular deaths each year and saves around £1.5 billion a year for healthcare services. In the United States, reducing salt intake by 3 g per day could prevent about 146,000 new cases of cardiovascular disease and more than 40,000 deaths per year. The health effects of achieving this reduction are almost comparable to those of reducing tobacco use or obesity [5]. It is estimated that in low- and middle-income countries, salt reduction will be more cost-effective, or at least comparable to tobacco control, in preventing cardiovascular disease.
A large portion of salt intake comes from salt added during cooking and/or salt used at the table as appropriate. Cooperate with the food industry to carry out public health campaigns, formulate salt reduction strategies according to the upper limit of salt intake (5 g/d) recommended by the Dietary Guidelines for Chinese Residents (2022), and measure salt consumption according to 24-hour urine sodium and dietary methods are all feasible measures in salt reduction plans. Achieving and sustaining salt reduction, even in small amounts, would have significant benefits globally, and at World Health Organization recommended levels, it could prevent an estimated 1.65 million cardiovascular disease-related deaths each year, with significant cost savings for individuals, families and health services. A study in northern China showed that children can play a key role in helping entire families reduce salt intake [6].
Bibliography:
1. Macgregor GA, Wardener HDJTL. Salt, Diet, and Health. 1999; 353: 1709.
2. Thout SR, Santos JA, McKenzie B, Trieu K, Johnson C, McLean R, Arcand J, Campbell NRC, Webster J. The Science of Salt: Updating the evidence on global estimates of salt intake. J Clin Hypertens (Greenwich). 2019,21(6):710-721. doi: 10.1111/jch.13546.
3. GBD 2017 Diet Collaborators. Health effects of dietary risks in 195 countries, 1990-2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet. 2019,393(10184):1958-1972. doi: 10.1016/S0140-6736(19)30041-8.
4. He FJ, Tan M, Ma Y, MacGregor GA. Salt Reduction to Prevent Hypertension and Cardiovascular Disease: JACC State-of-the-Art Review. J Am Coll Cardiol. 2020,75(6):632-647. doi: 10.1016/j.jacc.2019.11.055.
5. Bibbins-Domingo K, Chertow GM, Coxson PG, Moran A, Lightwood JM, Pletcher MJ, Goldman L. Projected effect of dietary salt reductions on future cardiovascular disease. N Engl J Med. 2010,362(7):590-9. doi: 10.1056/NEJMoa0907355.
6. He FJ, Wu Y, Feng XX, Ma J, Ma Y, Wang H, Zhang J, Yuan J, Lin CP, Nowson C, MacGregor GA. School based education programme to reduce salt intake in children and their families (School-EduSalt): cluster randomised controlled trial. BMJ. 2015,350:h770. doi: 10.1136/bmj.h770.
Author: LI Shenheng (Department of Nephrology, Zhujiang Hospital, Southern Medical University)
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