Thatās an interesting perspective! Youāre right that the scientific experts would disagree strongly on this, and to cite one of them: āWhile there is some controversy over the idea of a U or J-shaped curve for salt intake and cardiovascular outcomes, the more robust studies show that these use faulty evidence.ā Another expert adds to this, āIn healthy adults, sodium is needed to sustain BP, but we donāt observe a J-curve normally: there is sodium in all food, and the kidney is a great engine at holding on to sodium in low sodium settings, such that lower BP is basically almost always better).ā
I also donāt think itās accurate to say that the evidence is observational. (a) Aburto et alās (2013) meta-analysis of RCTs and prospective cohort studies shows that a reduction in sodium intake significantly reduced resting systolic blood pressure by 3.39 mm Hg; while Ettehad et alās meta-analysis entirely of RCTs shows that every 10 mm Hg reduction in systolic blood pressure significantly reduced the risk of major cardiovascular disease events (relative risk: 0.8), coronary heart disease (relative risk: 0.83), stroke (relative risk: 0.73) and heart failure (relative risk: 0.73), leading to a significant 13% reduction in all-cause mortality). (b) Then there is the Strazzullo et al meta-analysis of both RCTs and population studies, showing that additional sodium consumption of 1880 mg/āday leads to greater risk of CVD (relative risk: 1.14).
On the sweating issue (and hence the associated concerns about exercise and whether people in hot climates will be hurt) - I donāt think this is an unreasonable fear a prior, but the Lucko et al meta-analysis of RCTs suggests that 93% of dietary sodium is excreted via urine, so basically that should anchor our expectations that this isnāt going to be a significant way in which sodium is lost (let alone to such an extent that it has bad health consequences).
The existence of these meta-analyses is much less convincing than you think. One, because a study of the effect of sodium reduction on blood sugar combined with a study of the effect of antihypertensive medications donāt combine to make a valid estimate of the effect of sodium reduction on a mostly-normotensive population.
But second, because the meta-analyses are themselves mixed. A 2016 meta-meta-analysis of supposedly systematic meta-analyses of sodium reduction found 5 in favor, 3 against, and 6 inconclusive, and found evidence of biased selective citation.
Thatās an interesting perspective! Youāre right that the scientific experts would disagree strongly on this, and to cite one of them: āWhile there is some controversy over the idea of a U or J-shaped curve for salt intake and cardiovascular outcomes, the more robust studies show that these use faulty evidence.ā Another expert adds to this, āIn healthy adults, sodium is needed to sustain BP, but we donāt observe a J-curve normally: there is sodium in all food, and the kidney is a great engine at holding on to sodium in low sodium settings, such that lower BP is basically almost always better).ā
I also donāt think itās accurate to say that the evidence is observational. (a) Aburto et alās (2013) meta-analysis of RCTs and prospective cohort studies shows that a reduction in sodium intake significantly reduced resting systolic blood pressure by 3.39 mm Hg; while Ettehad et alās meta-analysis entirely of RCTs shows that every 10 mm Hg reduction in systolic blood pressure significantly reduced the risk of major cardiovascular disease events (relative risk: 0.8), coronary heart disease (relative risk: 0.83), stroke (relative risk: 0.73) and heart failure (relative risk: 0.73), leading to a significant 13% reduction in all-cause mortality). (b) Then there is the Strazzullo et al meta-analysis of both RCTs and population studies, showing that additional sodium consumption of 1880 mg/āday leads to greater risk of CVD (relative risk: 1.14).
On the sweating issue (and hence the associated concerns about exercise and whether people in hot climates will be hurt) - I donāt think this is an unreasonable fear a prior, but the Lucko et al meta-analysis of RCTs suggests that 93% of dietary sodium is excreted via urine, so basically that should anchor our expectations that this isnāt going to be a significant way in which sodium is lost (let alone to such an extent that it has bad health consequences).
The existence of these meta-analyses is much less convincing than you think. One, because a study of the effect of sodium reduction on blood sugar combined with a study of the effect of antihypertensive medications donāt combine to make a valid estimate of the effect of sodium reduction on a mostly-normotensive population.
But second, because the meta-analyses are themselves mixed. A 2016 meta-meta-analysis of supposedly systematic meta-analyses of sodium reduction found 5 in favor, 3 against, and 6 inconclusive, and found evidence of biased selective citation.