Nutrition and health

Objectives:
Does a low salt intake reduce blood pressure?

Study design:
This review article included 34 randomized trials with 3230 participants (the median age was 50 (range 22-73)), of which 22 were in hypertensive individuals and 12 in normotensive individuals. Of the 34 trials, 23 used crossover design and 11 used paralleled comparisons. 22 of the 34 trials were double blind, in 11 the observer was blind to blood pressure and one did not report any blinding procedure.

The study duration varied from 4 weeks to 3 years (median 4 weeks). With the usual salt intake the median 24 hour urinary sodium was 160 mmol (range 125-200 mmol), equivalent to a salt intake of 9.4 g/day (range 7.3-11.7 g/day) and the median blood pressure was 141/86 mmHg.

Despite the fact that only 7 out of 34 trials performed intention to treat analysis, the percentage of participants lost to follow-up after randomization was small (6.7% on average).

Results and conclusions:
The investigators found meta-analysis showed that the mean change in urinary sodium (reduced salt v usual salt) was -75 mmol/24 h (equivalent to a reduction of 4.4 g/day salt), and with this reduction in salt intake, the mean change in blood pressure was -4.18 mmHg [95% CI = -5.18 to -3.18, I2 = 75%] for systolic blood pressure and -2.06 mmHg [95% CI = -2.67 to -1.45, I2 = 68%] for diastolic blood pressure.

The investigators found meta-regression showed that age, ethnic group, blood pressure status (hypertensive or normotensive) and the change in 24 hour urinary sodium were all significantly associated with the fall in systolic blood pressure, explaining 68% of the variance between studies.

The investigators found a 100 mmol reduction in 24 hour urinary sodium (equivalent to a reduction 6 g/day salt) was associated with a fall in systolic blood pressure of 5.8 mmHg [95% CI = -2.5 to -9.2,  p = 0.001] after adjustment for age, ethnic group and blood pressure status.
For diastolic blood pressure, age, ethnic group, blood pressure status and the change in 24 hour urinary sodium explained 41% of the variance between studies.

The investigators found meta-analysis by subgroup showed that in people with hypertension the mean effect was -5.39 mmHg [95% CI = -6.62 to -4.15, I2 = 61%] for systolic blood pressure and -2.82 mmHg [95% CI = -3.54 to -2.11, I2 = 52%] for diastolic blood pressure.
In normotensive people, the figures were -2.42 mmHg [95% CI = -3.56 to -1.29, I2 = 66%] and -1.00 mmHg [95% CI = -1.85 to -0.15, I2 = 66%], respectively.

The investigators found further subgroup analysis showed that the decrease in systolic blood pressure was significant in both white and black people and in men and women.

The investigators found meta-analysis of data on hormones and lipids showed that the mean change was:
0.26 ng/mL/h [95% CI = 0.17 to 0.36, I2 = 70%] for plasma renin activity;
73.20 pmol/L [95% CI = 44.92 to 101.48, I2 = 62%] for aldosterone;
187 pmol/L [95% CI = 39 to 336, I2 = 5%] for noradrenaline (norepinephrine);
37 pmol/L [95% CI = -1 to 74, I2 = 12%] for adrenaline (epinephrine);
0.05 mmol/L [95% CI = -0.02 to 0.11, I2 = 0%] for total cholesterol;
0.05 mmol/L [95% CI = -0.01 to 0.12, I2 = 0%] for low density lipoprotein cholesterol (LDL-cholesterol or bad cholesterol);
-0.02 mmol/L [95% CI = -0.06 to 0.01, I2 = 16%] high density lipoprotein cholesterol (HDL-cholesterol or good cholesterol) and:
0.04 mmol/L [95% CI = -0.02 to 0.09, I2 = 0%] for triglycerides.

The investigators concluded a modest reduction in salt intake of 4.4 g/day for 4 or more weeks causes, from a population viewpoint, important falls in blood pressure in people with both raised and normal blood pressure.
Salt reduction is associated with a small physiological increase in plasma renin activity, aldosterone and noradrenaline and no significant change in lipid concentrations.
The current recommendations to reduce salt intake from 9-12 to 5-6 g/day will have a major effect on blood pressure, but a further reduction to 3 g/day will have a greater effect and should become the long term target for population salt intake.

Original title:
Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials by He FJ, Li J and MacGregor GA.

Link:
http://www.bmj.com/content/346/bmj.f1325

Additional information of El Mondo:
Find more studies/information on sodium intake and hypertension right here.
A daily diet with a maximum of 3 grams salt per day is a diet with a maximum of 0.15 gram salt per 100 kcal.
A daily diet with a maximum of 0.15 gram salt per 100 kcal is a diet with mainly products/meals with a maximum of 0.15 gram salt per 100 kcal.

Objectives:
The aim of this review article was to assess the relation between the level of habitual potassium intake and the incidence of cardiovascular disease (CVD).

Study design:
This review article included 15 cohort studies involving a total of 247510 male and female participants, 7,066 strokes, 3,058 coronary heart disease (CHD) events and 2,497 total CVD events.
The weighted average follow-up time was 12.2 years (range 5 to 19 years).
There was significant heterogeneity among studies in terms of sample size, duration of observation, number of events and difference in dietary potassium intake between the groups being compared. This heterogeneity led to a reduced statistical power in detecting a possible association between dietary potassium and coronary heart disease and cardiovascular disease.

There was no evidence of publication bias by the Egger test.

Potassium intake was assessed by 24-h dietary recall (n = 2), food frequency questionnaire (n = 6) or 24-h urinary excretion (n = 3).

Results and conclusions:
The investigators found in a pooled analysis, a dietary intake of 1.64g (42 mmol) potassium per day was significantly associated with a 21% lower risk of stroke [RR = 0.79, 95% CI = 0.68 to 0.90, p = 0.0007]. Significant means it can be said with a 95% confidence that a daily intake of 1.64g potassium really decreased the risk of having a stroke.

The investigators found a trend toward an inverse association between higher potassium intake (average weighted difference = 1.38g or 35.3 mmol/day) and risk of coronary heart disease [RR = 0.92, 95% CI = 0.81 to 1.04], which was not statistically significant [p = 0.18].
Not significant means it cannot be said with a 95% confidence that a daily intake of 1.38g potassium really decreased the risk of coronary heart disease with 8%. 

The investigators found a trend toward an inverse relationship between higher potassium intake (average weighted difference = 1.30g or 33.4 mmol/day) and cardiovascular disease risk [RR = 0.85, 95% CI = 0.62 to 1.16], which was not statistically significant [p = 0.31].

The investigators found a trend toward lower risk of CHD [RR = 0.93, 95% CI = 0.87 to 0.99, p = 0.03] and total CVD [RR = 0.74, 95% CI = 0.60 to 0.91, p = 0.0037] that attained statistical significance after the exclusion of a single cohort, based on sensitivity analysis.

The results of meta-regression analyses indicated that potassium intake difference, length of follow-up, quality score, recruitment year and population potassium intake at baseline were not significant sources of heterogeneity in the relationship of the potassium intake effect on the risk of CHD.

The results of meta-regression analyses indicated that the length of follow-up (coefficient: -0.064, 95% CI = -0.112 to -0.015, p = 0.01) and quality score (coefficient: -0.165, 95% CI = -0.287 to -0.043, p = 0.01) were significant sources of heterogeneity.

The investigators concluded that 1.64g dietary potassium per day decreases the risk of having a stroke and might also reduce the risk of coronary heart disease and total cardiovascular disease. This result applies to the general population, not only to specific subgroups at higher risk.
The favorable effects of dietary potassium were documented at least to some extent independently of other factors.
The results of this meta-analysis support recommendations for higher consumption of potassium-rich foods to prevent vascular diseases.

Original title:
Potassium Intake, Stroke, and Cardiovascular Disease : A Meta-Analysis of Prospective Studies by D'Elia L, Barba G, [...], Strazzullo P.

Link:
http://www.sciencedirect.com/science/article/pii/S0735109710049764

Additional information of El Mondo:
Find more information/studies on potassium right here.
The protective effect of potassium against the risk of stroke may conceivably relate to its blood pressure lowering effect.