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Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials

BMJ 2013; 346 doi: https://doi.org/10.1136/bmj.f1325 (Published 04 April 2013) Cite this as: BMJ 2013;346:f1325

Re: Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials

He and MacGregor distort our message. We do not claim that their analysis is similar to ours. On the contrary we emphasize the difference (167 references versus 30 references), but in spite of the difference the trends of the results are similar. The statistical differences may be due to differences in duration of treatment, or they may be due to statistical power. Furthermore, although blood pressure is associated with mortality, there is no evidence that sodium reduction reduces mortality mediated by a blood pressure reduction.

He and MacGregor repeat their well known arguments. In that context they refer to their analysis in the Lancet (1). This analysis is biased. The primary analysis by Taylor et al. (2) was designed and then conducted according to the design. He and MacGregor reorganized the data to give a result in accordance with their view. At the same time they avoided making the same analysis on the all cause mortality data, although the all cause mortality data were complete (available in 7 of 7 studies) in contrast to the CVD data (available in 4 of 7 studies). A similar analysis on the all cause mortality outcome from all 7 studies (or the 6 studies excluding the heart failure study) shows no difference between the usual sodium group and the reduced sodium group. Further, it should be emphasized that all the included studies with the exception of the heart failure study reduce sodium to a level above the recommended level (2000-2300 mg). So there is no evidence (not even He and MacGregor’s analysis) to prove beneficial effects on mortality of sodium reduction to a level below 2000 mg, which is the latest WHO recommendation, but there is non-optimal evidence in heart failure patients that a reduction below 2000 mg may be harmful. Concerning renin and aldosterone, these hormones increase slowly and linearly from 200 to 100 mmol of sodium, but below 100 mmol renin and aldosterone increase exponentially (3). A sodium intake below 100 mmol for the whole world’s populations is the goal of He, MacGregor and WHO - without any evidence of the possible consequences.

1) He FJ, MacGregor GA. Salt reduction lowers cardiovascular risk: meta-analysis of outcome trials. Lancet 2011;378:380-2.
2) Taylor RS, Ashton KE, Moxham T, Hooper L, Ebrahim S. Reduced dietary salt for the prevention of cardiovascular disease. Cochrane Database Syst Rev. 2011;7:CD009217.
3) Brunner HR, Laragh JH, Baer L, Newton MA, Goodwin FT, Krakoff LR, Bard RH, Bühler FR.Essential hypertension: renin and aldosterone, heart attack and stroke. N Engl J Med. 1972 Mar 2;286(9):441-9.

Competing interests: No competing interests

01 May 2013
Niels Graudal
Consultant
Gesche Jürgens
Copenhagen University Hospital
Blegdamsvej 9, DK-2100 Copenhagen