Salt and Cardiovascular Disease

Introduction

Heart disease, including conditions such as hypertension and cardiovascular disorders, remains a leading cause of morbidity and mortality worldwide. Lifestyle modifications, including dietary changes, play a crucial role in the management and prevention of heart disease. One such dietary modification is the reduction of salt intake.

Our diet is one of the most crucial factors that directly or indirectly affects our health and well-being. The age old saying “You are what you eat” could not hold more relevance in this context. Living in a world that is just emerging out of the clutches of the deadly COVID-19 pandemic, diet has never been a greater risk factor toward the development of cardiovascular disease (CVD).

The pandemic ravaged many lives either directly or indirectly. Many lost their lives, their loved ones, their health, but it also changed our lives forever. Today, we find a sharp rise in the number of overweight and obese individuals compared to the pre-pandemic era. A quick survey of your own friends and family will reveal that almost a near majority of individuals have gained an excess of body weight. Unhealthy eating habits and access to fast foods via the rise of food delivery apps have invited obesity and its associated diseases into our lives—an unhealthy food habit is now just a few clicks away, delivered right to the doorstep. Fast foods such as salted French fries and Chinese cuisine may contain as much as 7,000 mg of sodium in a single meal! The unregulated amount of salt in our diet has led to adverse cardiovascular consequences. There has been an alarming rise in young hypertension, metabolic syndrome, sleep apnea, and premature coronary atherosclerosis.

Salt, or sodium chloride, is a commonly used seasoning and preservative in food. Table salt consists of about 40% sodium and 60% chloride. While sodium is an essential mineral required for various bodily functions, excessive intake can have detrimental effects on cardiovascular health. High salt intake has been linked to hypertension, which remains one of the most significant causes of premature morbidity and mortality worldwide. It also contributes to fluid retention, strain on the heart, and an increased risk of stroke.

The Burden of Salt

The American Heart Association (AHA) has provided guidelines for salt intake to promote heart health. The general recommendation for the general population is to consume no more than 2,300 mg of sodium per day, which is equivalent to approximately one teaspoon of salt. However, for individuals with heart disease or those at a high risk, such as those with hypertension, diabetes, or chronic kidney disease, the recommended sodium intake is even lower—around 1,500 mg per day.

The average Indian adult consumes around 11 g of salt per day, which is more than double the recommended intake of salt and is much greater than the physiological requirement of the body.

Multiple studies have demonstrated a consistent relationship between dietary salt intake and blood pressure. A 4.4 g reduction in daily dietary intake of salt decreases blood pressure by about 4.2/2.1 mm Hg. In cohort studies, a 5 g per day higher salt intake (2,000 mg of sodium) is associated with a 17% greater risk of total CVD and crucially a 23% greater risk of stroke.

Reducing salt intake can be challenging, as salt is present in many processed and packaged foods, restaurant meals, and fast food. More than 70% of the salt we eat, according to the AHA, comes from processed, prepackaged, and restaurant foods. It is important for patients with heart disease to be aware of hidden sources of sodium and to make conscious efforts to limit their intake.

It is crucial for patients with heart disease to work closely with their healthcare providers and registered dietitians to develop personalized dietary plans. These plans should consider individual health conditions, medications, and specific nutritional needs.1^–6

The Dietary Approaches to Stop Hypertension Diet

The dietary approaches to stop hypertension (DASH) diet is a well-known eating plan that has been specifically designed to lower blood pressure and promote heart health. It emphasizes the consumption of nutrient-rich foods while limiting sodium intake, making it an excellent choice for individuals with hypertension. The DASH diet originated in the 1990s. In 1992, the National Institutes of Health (NIH) started funding several research projects to see if specific dietary interventions were useful in treating hypertension. Subjects included in the study were advised to follow just the dietary interventions and not include any other lifestyle modifications to avoid confounding factors. They found that only the dietary intervention alone could decrease systolic blood pressure by about 6–11 mm Hg. The effect on blood pressure reduction was seen both in normotensive and in hypertensive individuals. Based on these results, in some instances, DASH has been advocated as the first-line pharmacologic therapy along with lifestyle modification.7

The key features of the DASH diet include:

The DASH diet is not a restrictive or short-term diet but rather a sustainable and balanced approach to eating. It promotes a wide variety of foods, focusing on whole, unprocessed options and encourages portion control.

Sacks et al, in their study on the effects of reduced sodium and the DASH diet on blood pressure, found that as compared with the control diet, the DASH diet resulted in a significantly lower systolic blood pressure at every sodium level and in a significantly lower diastolic blood pressure at the high and intermediate sodium levels. The DASH diet had a greater effect on blood pressure at higher sodium levels than it did at lower levels of sodium (p < .001).8

A meta-analysis by Fillippou et al published in 2020 showed that, compared with a control diet, the DASH diet reduced both systolic blood pressure (SBP) and diastolic blood pressure (DBP) (difference in means: −3.2 mm Hg; 95% CI: −4.2, −2.3 mm Hg; p < .001, and −2.5 mm Hg; 95% CI: −3.5, −1.5 mm Hg; p < .001, respectively). Hypertension status did not modify the effect on BP reduction. The DASH diet compared with a control diet reduced SBP levels to a higher extent in trials with sodium intake >2,400 mg/d than in trials with sodium intake ≤2,400 mg/d, whereas both SBP and DBP were reduced more in trials with mean age <50 years than in trials of older participants. The adoption of the DASH diet was accompanied by significant BP reduction in adults with and without hypertension, although higher daily sodium intake and younger age enhanced the BP-lowering effect of the intervention.9

The blood pressure–lowering effect of the DASH diet seems to stem from its ability to cause natriuresis, which in turn exerts an influence on the renin–angiotensin–aldosterone system. This results in vascular and hormonal responses, which lead to a hypotensive effect. Sacks et al suggested that the BP-lowering effect of the DASH diet compared with the control diet was almost threefold higher for those at higher sodium intake than for those at lower sodium intake. The low dietary sodium probably countered the hypotensive effects of potassium, or probably, the high calcium or potassium content of the DASH diet countered the effects of low sodium.8^–12

The DASH diet also plays a role in the prevention of chronic heart failure as well as its management. Prospective observational studies have shown individuals adhering to a DASH pattern of eating have lower rates of heart failure incidence in women and also have a lower prevalence of hospitalization from heart failure and death in men.13

The DASH diet offers a well-rounded and evidence-based approach to managing hypertension. By adopting the principles of the DASH diet and making healthy food choices, individuals with hypertension can take proactive steps toward improving their cardiovascular health and overall well-being.

Effects on Salt on Cardiovascular Physiology6^, 14

The relationship between salt intake and CVD, particularly hypertension (high blood pressure), is well established. Excessive salt intake has been consistently associated with an increased risk of developing CVD, including heart disease, stroke, and other related conditions. Some of the effects of sodium on the cardiovascular system are as follows:

Adverse Effects of Going Too Low

While a low salt diet is recommended for individuals with hypertension or CVD, it is important to note that extreme or excessively restrictive low salt diets can have potential negative effects on heart health such as the following:

Salt and Heart Failure

A diet high in sodium is associated with an increased risk of cardiovascular comorbidities, especially hypertension and heart failure (HF). The prevalence of HF is rising all over the world, and in India, it is 1.2 per 1,000 population as per the UK–India Education and Research Initiative Study.15 An imbalance involving the renin angiotensin aldosterone system (RAAS) is the key pathogenic mechanism in the incidence or worsening of HF in patients consuming a high sodium diet. Imbalance of the RAAS system leads to sodium and water retention, leading to fluid overload manifesting as peripheral and pulmonary edema. An increase of 5 g salt a day leads to an extracellular volume expansion by almost 1.5 L, which leads to cardiac decompensation and HF. Excess salt is harmful both to patients suffering with HF with reduced EF (HFrEF) and to those with HF with preserved EF (HFpEF), though most of the data of benefit of salt restriction is with patients having HFrEF. Most studies on salt restriction have excluded patients with HFpEF. Dietary sodium retention is hence a mainstay in the management of HF. Patients with HF who actively adhere to a salt restricted diet benefit from a decrease in pulmonary capillary wedge pressure, decrease in extracellular fluid volume, decrease in arterial stiffness and systemic vascular resistance, suppression of oxidative stress and a decrease in aldosterone synthesis and its associated effects.15

A pilot trial, SODIUM HF (Study of Dietary Intervention under 100 mmol in HF), compared a low sodium (1.5 g/day) diet with a moderate sodium (2.3g/day) diet in HF patients. At six months’ follow-up, on the basis of a post hoc analysis based on the dietary sodium intake achieved (> or ≤ 1,500 mg/d) in all patients, the authors observed that there was a significant association between a sodium intake of ≤1,500 mg/d and improvement in BNP levels and quality of life.16

Another pilot study by Kalogeropoulos et al, the PROHIBIT (Prevent Adverse Outcomes in Heart Failure by Limiting Sodium) study, compared the effects of a 1,500 mg/day versus a 3,000 mg/day sodium diet in HF patients. The authors observed that while both meals were tolerated well by the participants, there was a significant improvement in the quality of life in the group restricting sodium intake to 1,500 mg/day but not in the 3,000 mg/day group. However, there was no significant difference in in the NTproBNP levels between groups. There was a significant reduction in the serum creatinine level in the 1,500 mg/day group.17

“Lite” Salt and Salt Substitutes: Hype or Hope?

“Salt Lite” is a term used to describe a type of salt that has a reduced sodium content compared to regular table salt. It is often marketed as a healthier alternative for individuals looking to lower their sodium intake or manage conditions such as hypertension or CVD.

Salt Lite typically contains a blend of sodium chloride (regular salt) and potassium chloride. Potassium chloride is used as a substitute for some of the sodium chloride to reduce the overall sodium content. Potassium is an essential mineral that helps regulate blood pressure and balance fluids in the body.

The primary purpose of Salt Lite is to provide a similar taste to regular salt while reducing the sodium content. However, it is important to note that while Salt Lite may be lower in sodium, it is not sodium free. It is still essential to use it in moderation and follow dietary guidelines recommended by healthcare professionals. Individuals considering using Salt Lite should be aware that it may have a slightly different taste compared to regular salt. Some people may notice a slight metallic or bitter taste due to the potassium chloride. It is advisable to try it in small amounts and gradually adjust to the taste if needed.

Potassium is an essential mineral that can help lower blood pressure. However, individuals with certain medical conditions, such as kidney disease or those taking certain medications, may need to limit their potassium intake.

The Salt Substitute and Stroke Study (SSaSS) was the largest clinical trial of salt reduction in cardiovascular events that evaluated the effect of replacing regular salt with salt substitute during cooking in Chinese participants. This study showed a reduction in the risk of stroke, major cardiovascular events, and all-cause mortality in the study group using a salt substitute compared to those using regular salt.24

Pink Salt: A Healthier Salt? No!

Pink Himalayan salt is chemically similar to table salt. It is a rock salt (halite) that is mined from the Punjab region of Pakistan. There is a common misconception that pink Himalayan salt is lower in sodium than regular table salt. However, both types consist of approximately 98% sodium chloride. The rest of pink salt consists of trace minerals, such as potassium, magnesium, and calcium. These give the salt its light pink tint and also explain why it tastes different from regular table salt. Himalayan salt carries the same risks as any other type of dietary sodium. Research has not shown that Himalayan salt has any unique health benefits compared to other dietary salt. The mineral impurities that give it a pink color, often promoted as healthful, are far too low in concentration to help with nutrition. One would have to eat a lethal amount of sodium to achieve helpful quantities of the other minerals! Hence, consuming pink salt with the notion that it is “healthy” can have disastrous consequences.

“Table Salt” and Its Effect on Cardiovascular Health

Despite having added salt in food while cooking, many individuals prefer adding salt “on-table” to cooked food. There has been a lot of interest in understanding if the frequency of adding salt to food has a direct implication on CVD events or subtypes. The frequency of adding salt to food may be considered a surrogate marker for long-term sodium intake.

In a recent study by Ma et al evaluating the relationship between frequency of adding salt to foods and CVD risk, the authors found that during a median follow-up of 11.8 years, lower frequency of adding salt to foods was significantly related to lower risks of total CVD events after adjusting for covariates and DASH diet. Compared to the group that always added table salt to foods, the group that never/rarely added table salt to foods was related to a 23%, 26%, and 37% lower risk of total CVD events, ischemic heart disease, and HF, respectively. Among the CVD subtypes, the strongest association was found between the risk of HF and lower frequency of salt intake, followed by a lower risk of ischemic heart disease. With relation to the DASH diet, participants with the lowest salt intake with highest adherence to the DASH diet had the lowest risk of total CVD events.25 This study corroborates the findings of a previous study26 which also reported that a higher frequency of adding salt to food was associated with a higher risk of all-cause premature mortality and lower life expectancy. A recent trial27 has also demonstrated a significant reduction in NtproBNP levels with dietary sodium reduction—a finding that reiterates that the greatest effect of salt restriction is on reduction of HF events. A strong relationship between the risk of ischemic heart disease and salt intake was also reported in a study from the Million Veteran Program.28

Conclusion

Excessive sodium intake by virtue of its propensity to retain water has been associated with an increase in blood pressure. Hypertension, a silent killer, is often the result of a disregard for salt restriction in diet. Hypertension contributes to an increased risk of other types of heart disease, stroke, or renal failure. Excessive sodium intake and uncontrolled blood pressure are major risk factors both for the development of HF and for episodes of decompensation in those with chronic HF. A low-sodium diet may help lower or prevent high blood pressure and may reduce the risk of CVD. Sodium-rich diets are also usually high in total fat and calories, which contribute to obesity and its myriad complications. A link between sodium intake and osteoporosis and stomach cancer has also been proposed. Salt begets salt! The more you eat a salty diet, the more your tase buds will crave a salty diet; hence, it is imperative to cut down on salt intake at the very roots.

Some practical tips to achieve a low-salt diet are as follows: