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:
Does iron supplementation during pregnancy improve maternal haematological status and birth weight?

Study design:
This review article included 48 RCTs (17,793 women) and 44 cohort studies (1,851,682 women).

The dose of iron in RCTs ranged from 10 mg to 240 mg daily. Duration of supplementation varied from 7 to 8 weeks up to 30 weeks during pregnancy.

Significant heterogeneity existed for several outcomes that could not be explained substantially by pre-specified subgroups.

Results and conclusions:
The investigators found iron supplementation during pregnancy increased maternal mean haemoglobin concentration by 4.59 g/L [95% CI = 3.72 to 5.46] compared with controls.

The investigators found iron with folic acid was associated with a significant increase in mean haemoglobin concentration of 10.41 g/L [95% CI = 5.36 to 15.46, I2 = 0%, 9 trials] and reduction in risk of anaemia in the third trimester or at delivery of 56% [95% CI = 0.37 to 0.53, I2 = 44%, 5 trials]. Significant means there is an association with a 95% confidence.

The investigators found iron supplementation during pregnancy significantly reduced the risk of anaemia with 50% [95% CI = 0.42 to 0.59] compared with controls.

The investigators found iron supplementation during pregnancy significantly reduced the risk of iron deficiency (of the mother) with 41% [95% CI = 0.46 to 0.79] compared with controls.

The investigators found iron supplementation during pregnancy significantly reduced the risk of iron deficiency anaemia with 60% [95% CI = 0.26 to 0.60] compared with controls.

The investigators found iron supplementation during pregnancy significantly reduced the risk of low birth weight (2500 g) with 19% [95% CI = 0.71 to 0.93] compared with controls.

However, the investigators found iron supplementation during pregnancy non-significantly reduced the risk of preterm birth with 16% [95% CI = 0.68 to 1.03] compared with controls. Non-significant means there is no association with a 95% confidence.

The investigators found in cohort studies that anaemia in the first or second trimester was significantly associated with a higher risk for low birth weight of 29% [adjusted odds ratio 1.29, 95% CI = 1.09 to 1.53] and preterm birth with 21% [adjusted odds ratio = 1.21, 95% CI = 1.13 to 1.30].

The investigators found in exposure-response analysis that for every 10 mg increase in iron dose/day, up to 66 mg/day, the relative risk of maternal anaemia was significantly 0.88 [95% CI = 0.84 to 0.92, p for linear trend 0.001].

The investigators found in exposure-response analysis that birth weight increased by 15.1 g [95% CI = 6.0 to 24.2, p for linear trend = 0.005] and risk of low birth weight significantly decreased by 3% [relative risk = 0.97, 95% CI = 0.95 to 0.98, p for linear trend 0.001] every 10 mg increase in dose/day.

Furthermore, the investigators found for each 1 g/L increase in mean haemoglobin, birth weight increased by 14.0 g [95% CI = 6.8 to 21.8, p for linear trend = 0.002]. However, mean haemoglobin was not associated with the risk of low birth weight and preterm birth.

The investigators found no evidence of a significant effect on duration of gestation, small for gestational age births and birth length and duration of iron use was not significantly associated with the outcomes after adjustment for dose.

The investigators concluded daily prenatal use of iron substantially improved birth weight in a linear dose-response fashion, probably leading to a reduction in risk of low birth weight. An improvement in prenatal mean haemoglobin concentration linearly increased birth weight and a linear decrease in maternal anaemia with higher doses of iron, up to 66 mg/day.

Original title:
Anaemia, prenatal iron use, and risk of adverse pregnancy outcomes: systematic review and meta-analysis by Haider BA, Olofin I, […], Fawzi WW.

Link:
http://www.bmj.com/content/346/bmj.f3443

Additional information of El Mondo:
Find more information/studies on iron and pregnancy right here.

Iron deficiency anaemia occurs when there isn't enough iron in the body. Anaemia is a condition where the amount of haemoglobin in the blood is below the normal level.
Iron deficiency anaemia has been defined as haemoglobin 110 g/L and serum ferritin 12 µg/L.