Role of no table salt on hypertension and stroke based on large sample size from National Health and Nutrition Examination Survey database

Hypertension is reported to be a major cause of premature deaths and a heavy burden of cardiovascular morbidity and mortality, which resulted in approximately 7.1 million deaths and an estimated cost of $48.6 billion ever year [1]. Hypertension is widely validated to increase the risk of developing cardiovascular diseases (CVD) such as coronary heart disease (CHD) and stroke [2, 3]. Hypertension has strong associations with atherosclerosis deposits blocking and narrowing brain arteries, which has become a major risk factor for the occurrence of stroke [4, 5]. Stroke is reported to be the leading cause of death in China and the second leading cause of death all through the world [6]. Stroke is also the main reason of long-term neurological disability in adults, which leads to a substantial economic burden to the society and a decreased quality of life in patients [7]. Considering the considerable amount of economic burden to the family and society, more effective health care planning and prevention of hypertension and stroke are necessary.

Currently, some researches proposed that lifestyle changes may have significant effects on blood pressure control [8]. As high salt intake was reported to be associated with the risk of hypertension and cardiovascular events, restricting dietary salt has been proposed to be a method for hypertension prevention [9, 10]. Salt reduction was considered to be an important dietary target for 2025 to reduce the mortality of main noncommunicable diseases by the World Health Organization (WHO) [11]. In recent years, low-salt diet or event no-salt diet was advocated to improve health and prevent some diseases [12]. Previously, a study reported that about 10% of the sodium intake comes from discretionary salt use including table salt and salt added while cooking, which can be controlled by individuals [13]. For some people, to control salt use in daily life indicated low salt or no salt indicate adding low or no salt at table, and some other people added lite salt or salt substitute at table. Lite salt or salt substitute refer to sodium chloride in traditional salt is partially replaced with potassium chloride or magnesium sulfate, which are considered as a strategy under consideration by several countries for lowing blood pressure [14]. At present, various studies have explored the associations between sodium intake and the risk of hypertension or stroke [3, 15]. High sodium intake was associated with increased risk of hypertension or stroke. People was advocated to reduced salt use. But for common people, monitoring the salt contributions of specific foods and food groups, differentiating the inherent and processing-added sodium content of foods or other dietary sources were difficult [13]. It is easier for controlling the discretionary salt use including table salt and salt added while cooking to achieve the sodium intake reduction. Previous studies were focused on the volume of salt intake with the risk of hypertension and stroke, whether the different types of salt used just at table or during cooking were associated with the risk of hypertension or stroke were still unclear. Thus, the associations of doesn’t add salt product or adding different varieties of salt at the table or during cooking in hypertension or stroke still needs investigation, which might provide a guide for salt use in common people in the prevention of hypertension stroke.

In the current study, the associations of different salt types added at table or no table salt with the occurrence of hypertension and stroke were assessed based on the data from National Health and Nutrition Examination Survey (NHANES) database.

In the present study, the data of 15,352 participants were collected from the NHANES database to analyze the associations of salt types added at table with hypertension and stroke. The result delineated that other salt intake or no table salt might be associated with an increased risk of hypertension. Other salt intake or no table salt might be also associated with an increased risk of hypertension and stroke. The findings of our study might give a reference for the use of salt at table in preventing the occurrence of hypertension and stroke and improving the prognosis of patients with hypertension or hypertension and stroke.

Currently, salt substitutes are used to replace ordinary salt (100% sodium chloride) where a portion of sodium is replaced with potassium chloride (usually 25%-30%) and/or magnesium sulphate (10%-14%). Several meta-analyses involving randomized controlled trials (RCTs) revealed that salt substitutes application decreased the systolic blood pressure and diastolic blood pressure in patients with hypertension [27]. Salt substitute might be an accessible and effective method for reducing the risk of death caused by stroke in patients with hypertension [28]. In this study, patients with other salt intake (lite salt or salt substitute) were associated with a higher risk of hypertension or hypertension and stroke. Some studies have indicated that people may prefer the taste of ordinary salt to salt substitutes and some people do not accept the taste of salt substitutes, so when they use salt substitutes, they might use more amount of salt, which actually resulted in a high sodium intake [29]. In addition, we found for people with more salt substitutes at table, the potassium intake was lower than those with ordinary salt intake (Supplementary Fig. 2). Previous studies have revealed that potassium is an essential nutrient and the addition of a high potassium diet could reduce the blood pressure in people [30, 31]. Also, some randomized controlled trials indicated that higher potassium intake could lower the blood pressure in those with hypertension [32]. Therefore, adequate potassium supplement was recommended in people especially hypertension people.

As for people do not add salt product at the table, excessive low salt diet might cause salt-sensitivity hypertension, as long-term low sodium intake might result in the high sensitivity to salt in human body and increased sodium intake might stimulate the secretions of hormones such as epinephrine and angiotensin, which led to hypertension [33]. Salt-sensitivity hypertension was a potential area requiring validation for further research, as some other researchers indicated that although a high-salt diet might increase the accumulation of sodium, the expansion of volume, and the adjustment of cardiac outputs, the autoregulation might maintain the flow via increasing the systemic vascular resistance, and causing the kidneys to excrete more salt and water, and therefore reducing systems to normal and minimizing the changes in blood pressure [34]. Another study also depicted that sodium reduction only decreased the blood pressure in participants with a blood pressure in the highest 25th percentile of all population and the author also suggested to reframe the policy of lowering dietary sodium intake in the general population and hypertension patients [35]. Sodium is main extracellular cation in the body to maintain intravascular volume, which is required in human body and salt restriction in humans may cause some adverse effects [36]. A previous study also reported that salt-deficient diet promoted cystogenesis in ARPKD via epithelial sodium channel [37]. Besides, people might intake more sodium rather than eat at table. Nowadays, commercial products infiltrate sodium insensibly into our nutrition and the involuntary sodium intake was high in daily life [38]. People who used other salt or do not add salt at table might prefer other commercial products with high sodium.

The findings of our study suggested that adding ordinary salt at table with appropriate volume is recommended for the prevention of hypertension. In addition, for people with hypertension or hypertension and stroke, adding lower volume of ordinary salt at table as well as enough potassium supplement were necessary for blood pressure control. This study measured the associations of salt with hypertension and stroke based on the data of 15,352 subjects from NHANES database. Our study involved in a large sample size and subgroup analysis was conducted in different types of salt, which might increase the reliability of our results. The findings of our study might provide a reference for the salt use at table or during cooking for common people. Several limitations existed in the current study. Firstly, the participants included in NHANES database were mainly from western countries, and whether the findings were suitable for people from oriental countries still needs validation in more studies. Secondly, the sample size in other salt group was small, which might decrease the statistical power. Thirdly, all data were collected from NHANES database, and important variables such as 24-h urine sodium of participants were not evaluated; the outcome variables were self-reported, which might cause bias. Fourthly, the self-reports of prior stroke in the NHANES stroke data represents a sample of stroke survivors, and we couldn’t analyze the data on those with acute stroke die, or are disabled to the extent that they are hospitalized, home-bound or institutionalized in long term care facilities. In the future, RCTs including large scale of sample size were required to verify the results in this study.

This study analyzed the associations of different salt types and no table salt with hypertension and stroke based on the data of 15,352 subjects NHANES database. The results delineated that no table salt was associated with a higher risk of hypertension or hypertension and stroke. The findings suggested that salt intake is important and required in common people and in patients with hypertension or hypertension with stroke, necessary ordinary salt intake and enough potassium intake were required to control the blood pressure.