The effectiveness of salt restriction versus other non-pharmacological approaches to prevent or control arterial hypertension

Introduction

Lifestyle changes are the first step in a strategy to treat hypertension that may be or not be followed by pharmacological treatment, depending on blood pressure (BP) levels and/or patient cardiovascular risk [1].

The main strategies to improving quality of life are [1,2]:

• a reduction in salt intake
• an increase in potassium intake
• regular physical activity
• adequate weight control
• control of alcohol consumption
• cessation of smoking

Sodium (Na+) is a common component in different nutrients included in a normal diet. The global sodium intake, especially in industrialised populations, is around 10 g per day [3], despite the World Health Organization (WHO) recommendation of less than 5 grs per day (https://www.who.int/elena/titles/guidance_summaries/sodium_intake/en/).

Salt is not the same as sodium; salt is chemical sodium chloride (NaCl) and this is very important when talking about numbers: 10 gr of salt contains plus/minus 5 gr of sodium.

The major intake of sodium comes from industrialised foods, where it is used as a preservative (i.e., canned foods), to enhance flavours and to maintain meat colour and volume, among other uses. Through these products the hidden sodium in manufactured products has become a global health threat.

Available evidence [4] supports the theory of a direct relationship between Na+ intake and BP values, since the excessive consumption of sodium is responsible for not only the increase in BP but also for the onset of arterial hypertension and its cardiovascular complications, gastric cancer, and osteoporosis. In addition, a reduction in sodium intake is also responsible for a reduction in cardiovascular morbidity and global mortality [4].

Thus, the aim of the present review is to compare the efficacy of salt intake reduction on arterial hypertension and to compare it with diet, the reduction in alcohol intake, regular physical activity, the maintenance of appropriate weight and quitting smoking, either alone or as a combined strategy.

Salt restriction and other non-pharmacological strategies

Non-pharmacological BP reduction strategies are comprised of various parameters. To understand what lifestyle changes would best benefit your patient it is important to consider current evidence. Below we summarise current literature, seeing how reduction in salt intake compares to other lifestyle strategies in lowering BP.

Why sodium reduction?

A meta-analysis including 34 trials [5] showed, in hypertensive and normotensive subjects, that a reduction in salt intake to lower than 4.4 g/day was able to induce a -4.18/-2.06 mmHg decrease in SBP and DBP, respectively, with no gender or ethnicity related differences. Comparing normotensive to hypertensive subjects, with a reduction of 100 “mmol” in 24h urinary sodium excretion, the normotensive group had a mean fall in SBP of 2.42 mmHg and 1 mmHg in DBP, while in hypertensive patients the fall was -5.39/-2.82 mmHg, respectively.

Furthermore, a systematic review and meta-analysis of 133 studies (12,197 participants) [6], analysing the effect of proportional reduction in salt intake to BP reduction, showed that for each 50 “mmol” decrease in 24h urinary sodium excretion, a reduction in 1.10 mmHg in SBP and a 0.33 mmHg in DBP was observed. The mean reduction of sodium intake was 130 “mmol” and the mean reduction of blood pressure was -4.26 and -2.07 mmHg for SBP and DBP, respectively. Once again, the reduction in BP was observed in both hypertensive and normotensive subjects. However, a greater reduction in BP was reported in subjects with higher blood pressure, as well as in older people.

Recently Filippini et al. [7] analysed 85 trials using a statistical analysis of the dose-response curves between sodium intake and BP. The trials included normotensive and hypertensive subjects with a range of sodium intake between 0.4 and 7.6 g/day and measured 24 h urinary sodium excretion, SBP or DBP or both as a main outcome. The results showed a linear dose-response effect, given the wide range of sodium intake, with the change -15 mmHg in SBP and almost -10 mmHg in DBP. Like other meta-analysis results, the reduction of 100 “mmol” /day in urinary sodium excretion was associated with a mean decrease of -5.56 mmHg in SBP and -2.33 mmHg in DBP. Coinciding with previous data, when comparing hypertensive to normotensive subjects, a greater BP reduction was observed in the hypertensive group (-6.5/-3.0 mmHg) compared to normotensive subjects (-2.3/-0.8 mmHg).

Which diet?

The Dietary Approaches to Stop Hypertension (DASH) [8] study proved that a diet mainly composed of fruits, vegetables, and low-fat dairy products, together with small amounts of red meat, and low total and saturated fats, was able to induce a decrease in blood pressure, not only in hypertensive patients but also in normotensive subjects.

Compared to a control diet, subjects on a DASH diet had a lower baseline BP (-5.9/-2.9 mmHg). When combined with low salt intake, the decrease in blood pressure was greater than either of these strategies alone. In subjects with a regular diet (USA population) who had both a higher sodium intake and baseline BP, reducing sodium intake from 150 “mmol” to 100 “mmol” per day reduced SBP by 2.1 mmHg. In subjects on a DASH diet with a lower sodium intake and BP, the reduction in SBP was -1.3 mmHg. Reducing the sodium intake from the intermediate (100 “mmol” per day) to the lower level (50 “mmol” per day) caused an additional reduction in SBP of -4.6 mmHg on a control diet and -1.7 mmHg on the DASH diet. These effects were observed in subjects with or without hypertension, the reduction being greater in those who initially had higher sodium intakes.

What about potassium?

Several studies have shown that potassium (K+), an essential nutrient required for the maintenance of total body fluid volume, acid and electrolyte balance, normal cell function, and cardiac activity, seems to be involved as well in the decrease of blood pressure. However, greater amounts of potassium are found in diets rich in vegetables and fruits and in industrialised foods the potassium content is low.

A meta-analysis of 15 randomised controlled trials [9], in patients with and without pharmacological treatment, looked for the relationship between potassium supplementation and BP. It showed that potassium supplementation resulted in a BP reduction of -4.7/-3.5 mmHg (SBP/DBP). This decrease was greater in hypertensive patients, (SBP -6.8/DBP -4.6 mmHg).

In another randomised placebo-controlled, crossover study [10] in which untreated patients with a mean SBP of 145 mmHg received 4 weeks of supplemental K+ (3 g/day) and a diet relatively low in Na+, a reduction in SBP of -3.9 mmHg was reported.

However, until now the published data failed to provide strong evidence to support the effects of K+ on blood pressure or a dose-response interaction of K+ with BP values [11]. Nevertheless, the reduction in sodium/potassium ratio seems to have a relevant role and seems to be a useful tool when considering the reduction in BP [12].

What about alcohol consumption?

There is a proven relationship between alcohol consumption and BP, hypertension, and cardiovascular risk [1,2]. A meta-analysis of longitudinal studies [13] showed that alcohol intake beyond two drinks per day (12 g of pure ethanol per drink) was consistently associated with an increased incidence of hypertension in both men and women. This is the cut-off value recommended by the European [1] and the International [2] Societies of Hypertension (ESH, ISH, respectively).

The Prevention and Treatment of Hypertension Study (PATHS) [14] investigated the effects of alcohol reduction on BP and showed a modest BP reduction (1.2/0.7 mmHg) compared to the control group, after 6 months of follow-up.

Does physical activity really matter?

The evaluation of 17 meta-analyses and one systematic review [15] aimed to show the relationship between physical activity (PA) and the prevention or treatment of hypertension in subjects with BP lower than 120/80 mmHg or between 120/80 and 139/89 mmHg with no physical activity at baseline. It showed that increasing from low to vigorous levels of exercise led to a decrease in -2 to -5 mmHg in SBP and -1 to -4 mmHg in DBP.

Subjects with a moderate leisure time physical activity lowers the risk of incident hypertension by 11% and in subjects with high leisure time physical activity, the risk was decreased in a 19%. In subjects with hypertension, increasing from low to vigorous levels of exercise led to a BP decrease ranging from -5 to -17mmHg in SBP and -2 to -10 mmHg for DBP.

Different kind of exercises have been demonstrated to be beneficial for lowering BP. A meta-analysis of 93 trials [16] found that endurance, dynamic resistance, and isometric resistance training decreased BP in -3.5/-2.5 mmHg, -1.87/-3.2 mmHg and -10.9/-6.2 mmHg, respectively.

Finally, high intensity exercise failed to show any difference in the BP reduction compared to moderate intensity training [17].

In this way, the ESH/ISH Guideline’s recommendations are for moderate dynamic exercise performed at least 30 minutes per day, 5 to 7 times per week [1,2].

How about weight reduction?

In obesity, visceral fat is mainly associated with higher risk for hypertension, dysglycaemia, dyslipidaemias, metabolic syndrome, and cardiovascular morbidity and mortality. It is also involved in the mechanisms related to the stimulation of the renin-angiotensin-aldosterone system, the increased sympathetic nervous system activity, and renal dysfunction [18].

A meta-analysis including 25 randomised controlled trials (4,874 subjects) evaluated the effect of weight reduction on blood pressure [19]. Among the subjects, fifty percent had hypertension and 24% were treated with antihypertensive medication. A 5.1 kg reduction in body weight reduced SBP by 4.44 mmHg and DBP by 3.57 mmHg. In addition, for each 1 kg reduction in body weight, there was a decrease of 1.05 mmHg in SBP and 0.92 mmHg in DBP. The SBP and DBP reduction was larger in patients under pharmacological treatment. In this study, both the energy restriction and the increased physical activity helped reach the targets proposed. So, it is important to consider when analysing weight reduction, that the efficacy of diet with or without physical activity is involved in reaching the targeted weight goals.

Tobacco use?

Cigarette smoking is related to an increased risk of cardiovascular disease through different mechanisms, including oxidative stress, inflammatory mechanisms that lead to endothelial dysfunction, and reduction in arterial elasticity [20]. Although smoking induces a direct activation of the sympathetic nervous system, causing acute increases in blood pressure resulting from vasoconstriction and tachycardia, there is no clear evidence for a direct causal relationship between cigarette smoking and the risk of hypertension.

Putting it all comes together: what are the overall effects of the association of lifestyle components and BP?

Different authors report a decrease in BP or the prevention of arterial hypertension through lifestyle modifications.

Geleijnse et al. [21] analysed the risk of developing hypertension when different dietary and lifestyle conditions were implemented. Results showed that reducing sodium intake to 2.1 g/day leads to a decrease in SBP and DBP of -2.5 mmHg and -2.0 mmHg, respectively. On the other side, a 2g/day increase in dietary potassium induced a BP reduction of -2.4 mmHg for SBP and -1.6 mmHg for DBP.

Two and a half hours of physical activity per week showed a reduction in SBP and DBP of -2.8/-1.8 mmHg, respectively.

Reducing body weight by 6.5 kg decreased SBP by -4.8 mmHg and DBP by -3.4 mmHg.

Finally, reducing the alcohol intake to less than 41 ml reduced BP in -2.6 mmHg for SBP and -1.4 mmHg for DBP.

Organia et al [22], analysed several trials and reported the effects of different lifestyle changes on BP. They reported a mean change in BP with salt restriction between -4.7 to -3.7 mmHg for SBP and -2.0 to -2.5 mmHg for DBP. Changing dietary patterns, especially to a DASH diet, leads to a mean decrease in BP that varies between -11.1 to -4.3 mmHg for SBP and -6.4 to -2.4 mmHg for DBP. Regular physical activity showed a mean change in SBP of -12.4 mmHg to -2.58 mmHg and -4.9 to -2.6 mmHg for DBP.

Weight control decreases SBP in a range of -6.4 to -2.9 mmHg and -3.7 to -2.3 mmHg in DBP.

Reduction in alcohol consumption showed a mean fall of -3.2/-2.0 mmHg in SBP and DBP, respectively.

This data is summarised in Table 1, where we represent the efficacy of the aforementioned lifestyle strategies. The last line is a calculation of the mean efficacy for each one, in order to compare their differences in efficacy.

Table 1. Reduction in blood pressure Induced by life-style components.

The Blood Pressure (BP) decrease induced in different studies (5-8) or meta-analyses (18,19), by the different components of lifestyle change.

Na+: sodium intake reductions, K+: potassium intake increase, Diet: calories and quality of food recommended, PA: physical activity, W: weight reduction, Alcohol: alcohol intake reduction to recommended drinks/day

We see that there is a high heterogeneity in the results reported. However, when calculating the mean decrease induced in BP, diet has the greater efficacy (-7.3/-3.8 mmHg) followed by weight control (-4.5/-3.3 mmHg). A reduction in Na+ intake (-3.8/-2.2 mmHg), as an increase in potassium intake (-3.55/-2.6 mmHg), and physical activity (-3.9/-2.2 mmHg), showed similar efficacy, being slightly lower than weight reduction.

The control in alcohol consumption showed the lowest efficacy in reducing BP (-2.3/-1.7).

Conclusions

When all the data is taken into consideration, it seems clear that a reduction in daily sodium intake induces a decrease in blood pressure either in normotensive or hypertensive subjects. The efficacy was similar to physical activity and the increase in potassium intake but lower than diet modification and weight reduction.

A reduction in alcohol intake, while having the lowest efficacy, should still be indicated for patients due the high prevalence of alcoholism.

Finally, these differences in efficacies do not prevent the use of any of these as combined strategies, because when added together, they show a greater efficacy in reducing BP in normotension individuals and in preventing arterial hypertension.

Take Home messages

1. Reducing sodium (around 2,3 g/per day) and increasing potassium (around 3 g/day) intakes are the main tools for preventing and treating hypertension. Salt is not the same as sodium; salt is chemical sodium chloride (NaCl) and this is very important when talking about numbers: 10 gr of salt contains plus/minus 5 gr of sodium.
2. Diet and weight reduction must be considered in the treatment of hypertension.
3. A reduction in alcohol intake must be recommended, specifically in heavy drinkers, to fewer than 14 or 8 units per week for men and women, respectively.
4. The physical activity recommended practice is, at least, 30 min of moderate, dynamic exercise, 5-7 days per week. This will improve not only BP reduction but also weight control.