A year study links a diet very high in salt to a higher risk of heart failure. Study shows possible connection, but other factors may be important The increased risk may be due to high blood pressure, coronary disease. The increased risk of cardiovascular events associated with higher sodium By how much does dietary salt reduction lower blood pressure? .. Sodium excretion and risk of developing coronary heart disease. The association between dietary sodium intake, ESRD, and all-cause mortality in patients with type 1 diabetes. The connection between high salt intake and elevated BP high BP was lowered by a low salt diet and a renewed salt .. The hazards ratios for coronary heart disease.
However, limitations include recall bias, variations of sodium content of common food items e. In general, dietary methods of assessment underestimate sodium intake, compared with 24 h urinary measures. Between-study differences in the methods of measuring sodium intake make between-study comparisons difficult. For example, dietary methods may underestimate sodium intake compared with urinary methods, and, therefore, studies employing dietary methods may observe lower absolute thresholds of sodium intake associated with CV risk.
Cardiovascular and other effects of salt consumption
One approach is to confine analysis to studies that used reference standard 24 h urinary collections to estimate sodium intake. Of eight prospective cohort studies, 512—1421—24 two reported a positive association, two reported no association, and four reported an inverse association between sodium intake and some CV events. Differences in the methods of measurement also present problems for implementation and monitoring of guideline recommendations. For example, guideline thresholds are primarily based on estimates from clinical trials examining the effects of a sodium-lowering diet on blood-pressure lowering which used 24 h urinary estimates of sodium intake.
However, most population-based surveys of sodium intake in communities have used dietary recall methods. In studies that compared 24 h urinary sodium to 24 h dietary recall, correlations were poor to moderate.
To this end, future studies should ensure that both dietary and urinary methods of sodium intake are measured. Variations in population characteristics Geographical region and range of sodium intake A meta-analysis 26 of 13 prospective cohort studies reported a significant association between increased sodium intake and CV events and stroke.
Journal of Human Hypertension. How far should salt intake be reduced? Salt intake, Stroke and Cardiovascular Disease: Prevention of Cardiovascular Disease. Public health guidance Salt intake and stroke: Schmeider RE et al. A determinant of cardiac involvement in essential hypertension. Kupari M et al. Correlates of left ventricular mass in a population sample aged 36 to 37 years. Focus on lifestyle and salt intake.
Sodium and left ventricular mass in untreated hypertensive and normotensive subjects. American Journal of Physiology. Ferrara LA et al. Left ventricular mass reduction during salt depletion in arterial hypertension. Liebson PR et al. Comparison of five antihypertensive monotherapies and placebo for change in left ventricular mass in patients receiving nutritional-hygienic therapy in the Treatment of Mild Hypertension Study TOMHS. Jula AM et al.
Dietary Salt Intake and Hypertension
Furthermore, it also found that populations with low average daily salt intakes had low BP and very little or no increase in BP with age Mean sodium excretion was 0. Mean BP was Systolic and diastolic BP were not higher at older than at younger ages in men. In women, systolic pressure was lower at older ages.
In this tribe, there was a low average population BP, no hypertension and no positive slope of BP with age in a population with very low salt intake. Salt institute criticized that in an initial analysis of 48 of the 52 centers, no significant association was noted between sodium intake and median BP.
However, the INTERSALT's investigators re-analyzed their data and showed that the highly significant within-population association between salt intake and BP across all 52 centers was virtually unchanged.
Lowering sodium intake by mmol was associated with a 3mmHg decrease in systolic BP There are several studies on the effect of reducing the salt intake on BP on a community levels. In the intervention community, there was a widespread health education effort to reduce the dietary salt intake. The fall in BP involved the whole community, normotensives and hypertensive individuals alike, and the response did not differ between the young and the old or between men and women.Mayo Clinic Minute: Spice things up to lower salt intake
Those with the greatest fall in salt excretion tended significantly to be also those who showed the greatest fall in BP. The other long-term trial was carried out in Tianjin in China as part of a community-based intervention program to reduce non-communicable diseases This intervention was based on examinations of independent cross-sectional population samples in 1, persons and 2, persons in the intervention and matched reference areas. The food recall method was used to measure dietary salt intake.
The mean reduction in salt intake was 1. During the same period, the sodium intake increased significantly in men of the reference area. In the intervention area, the mean systolic BP decreased by 3mmHg for the total population and by 2mmHg for normotensive people.
The decrease in systolic BP was significant for both hypertensive and normotensive subjects. Another long-term trial was performed in two Belgian towns of 12, and 8, inhabitants, situated within 50 km of each other The low-sodium intervention in one town was mainly directed at women and implemented through mass media techniques, while the control town was merely observed. During the study a total of 2, subjects were examined.
Cardiovascular and other effects of salt consumption
However, both systolic BP No significant difference was observed in the evolution of mean systolic and diastolic pressures that declined to the same extent in the two towns during the trial.
In women of the intervention town, hour urinary salt excretion decreased by 1. This negative result may be explained by the small reduction in salt consumption that would be insufficient to observe a net effect on BP in the Belgian environment.
These results suggest that a reduction in salt consumption is difficult to achieve with mass media techniques and in women and in subjects aged 50 years or more, the intervention did achieve some success, but BP was not affected. There were many randomized clinical trials performed to test the effects of reducing salt intake on BP. Thirty-two trials with outcome data for 2, subjects were included. Pooled BP differences between treated and control groups were highly significant for all trials combined.
The effects on blood pressure by lowering sodium in hypertensive and normotensive subjects were Weighted linear-regression analyses across the trials showed dose responses, which were more consistent for trials in normotensive subjects.
These analyses yielded estimates, per mmol of sodium reduction, of There is no evidence that sodium reduction as achieved in these trials presents any safety hazards. They concluded that the BP reduction with a substantial lowering of dietary sodium in the US population could reduce cardiovascular morbidity and mortality.
However, in two other meta-analyses 3435it was claimed that salt reduction had very little effect on BP in individuals with normal BP and a reduction in population salt intake was not warranted. The meta-analysis by Midgley et al. Decreases in BP were larger in trials of older hypertensive individuals and small and non-significant in trials of normotensive individuals.
They concluded that dietary sodium restriction for older hypertensive individuals might be considered, but the evidence in the normotensive population does not support current recommendations for universal dietary sodium restriction. Another meta-analysis by Graudal et al. They concluded that these results do not support a general recommendation to reduce sodium intake. However, these two meta-analyses were criticized by some authors because the data included was flawed.
Both meta-analysis included trials of very short duration with comparing the effects of acute salt loading to abrupt and severe salt restriction for only a few days. It is inappropriate to include the acute salt restriction trials in a meta-analysis where the implications of the findings are to apply them to public health recommendations for a long-term. It is possible that acute and large reduction in salt intake increases sympathetic activity, stimulates the renin-angiotensin system which would counteract the effects on BP.
Subsequently, several large-scale intervention studies showing significant antihypertensive effects of salt reduction in diet were performed by several groups. In TOHP I 36the patients were randomized to three life-style change groups weight reduction, sodium reduction, and stress managementone of which was a low sodium diet.
At 18 months follow-up, weight reduction intervention produced weight loss of 3. They concluded that weight reduction was the most effective strategy tested for reducing BP in normotensive persons. Sodium reduction was also effective for reducing BP. Compared with the usual care group, BP decreased 2.
At 36 months, BP decreases remained greater in the active intervention groups than in the usual care group weight loss group, 1. Differences were statistically significant for systolic BP in the sodium reduction group. TOPH I and II will presumably remain the best evidence supporting the beneficial effect of a moderate reduction of salt intake in the general population The intervention studies of salt intake reduction are often conducted with other life-style modifications.
TONE study 39 was performed to determine whether weight loss or reduced sodium intake is effective in the treatment of older persons aged 60 to 80 years with hypertension. The authors randomized obese participants to reduced sodium intake, weight loss, both, or usual care, and the non-obese participants to reduced sodium intake or usual care. After a median follow-up of 29 months range monthsthe composite outcome occurred less frequently among those assigned vs.
The mean change in blood pressure for participants assigned to sodium reduction alone was This study, however, has to be interpreted with caution including selection of adherent and well educated patients only There was no difference between sodium-restricted and control patients in the incidence of cardiovascular events 44 [ TONE study showed significant antihypertensive effects of salt reduction in diet.
The level of salt restriction effective for maintaining a normal BP after the discontinuation of an antihypertensive drug was TONE study demonstrated that a reduced sodium intake and weight loss, alone or combined, could effectively control hypertension Another well-conducted landmark study was the DASH Dietary Approaches to Stop Hypertension -Sodium trial 40a week well controlled feeding trial provided the most robust evidence about the effect of salt intake on human BP.
Each intake of salt was maintained for 30 days. Two different diets that is the control diet and the DASH diet, which is rich in fruits, vegetables and low-fat dairy products, were tested.
Dietary Salt Intake and Hypertension
When the participants were shifted from a high sodium diet to a normal sodium diet, the systolic BP decreased by 2. When they were shifted from a normal sodium diet to a low sodium diet, there was a further reduction in systolic BP of 4. The adherence to the diet of participants was monitored, not only by measuring hour urine sodium at the end of each period but also their daily food diaries.
There was a very significant difference in systolic The blood pressures were all significantly lower on the DASH diet.
There was a greater reduction in systolic pressure when blood pressure was initially high and in women, but most importantly the blood pressure-lowering effect of reducing the salt intake was observed in all categories of the population, in particular in normotensive as well as in hypertensive people.
The DASH-sodium trial supports that a low sodium diet leads to lower blood pressure. This observation is very important for the public health issue of lowering salt intake. Most acknowledge that this study reliably confirmed the benefit of dietary sodium restriction in BP management.
However, the DASH diet was significantly different from the control diet in terms of more fruits, vegetables, low-fat dairy foods, fish, nuts, potassium, calcium, magnesium, and dietary fiber. Although the group on the DASH diet had a lower urinary sodium excretion, this does not necessarily imply that the benefit was being solely caused by a dietary sodium reduction. In addition, this study did not evaluate the long-term effects of the intervention and the clinically relevant variables, such as mortality or morbidity.
InHe and MacGregor 41 demonstrated that a modest salt intake reduction caused significant falls in BP in both hypertensive and normotensive individuals. The median reduction in hour urinary sodium excretion was 78 mmol in hypertensives and 74mmol in normotensives.
The pooled estimates of BP fall were 4. Weighted linear regression analyses showed a dose response relationship between the change in urinary sodium and BP. They demonstrated that a modest reduction in salt intake for a duration of 4 or more weeks does have a significant and important effect on BP in both hypertensive and normotensive individuals. These findings in conjunction with other previous evidence relating salt intake to BP make a strong case for a reduction in population salt intake, which will lower population BP and therefore reduce cardiovascular mortality.
Many meta-analyses, so far, on the effect of salt reduction on BP have shown consistent reductions in BP in those with high blood pressure, but there has been some controversy about the magnitude of the fall in BP in normotensive individuals 34 In these two meta-analyses, it was claimed that salt reduction had no or very little effect on blood pressure in normotensive individuals.
However, detailed examination of these two meta-analyses showed that their data collection and analysis were flawed. Recently, there has been a hot debate whether current salt intake is too high from a health perspective. There were studies reporting the influence of salt intake on overall cardiovascular diseases such as He et al. They suggested that salt reduction prevented the onset of cardiovascular diseases. They also found that it was the obese and not the non-obese who benefited.
The hazards ratios for coronary heart disease, cardiovascular disease, and all-cause mortality, associated with a mmol increase in 24 hour urinary sodium excretion, were 1.