Editor—Little et al address an important topic in their trial of dietary advice for patients with a single high blood pressure reading in primary care.1 Robust evidence from randomised controlled trials of the effectiveness of nurse led hypertension management in primary care is lacking.2 No mention is made of a possible cluster effect of different practices, neither do the authors clarify whether randomisation was balanced within practices. Neither nurses assessing outcomes nor patients were blinded to the intervention arm.
Figure 1.
Credit: PENNY GRET/ARS
The entry assessment of blood pressure does not follow guidelines from the British Hypertension Society (neither does that at six months), which indicates that at least two measurements (1-2 minutes apart) should be taken on each occasion.3 The patients enrolled would probably have had normal blood pressure and therefore would have been less likely to respond to treatment, since the blood pressure response to any treatment is greater the higher the blood pressure.
A reduction of sodium intake to < 100 mmol/day (or to < 6 g salt) would be expected to reduce systolic blood pressure by 2-8 mm Hg.3 Low sodium salt achieved a reduction in sodium to potassium ratio of 0.32 (95% confidence interval 0.08 to 0.56). This is comparable to the changes seen in older patients with a higher blood pressure.4 Nevertheless, a 1.3 mm Hg lower systolic blood pressure at one month and 1.4 mm Hg at six months is observed, although this does not reach significance.
This is exactly the effect on blood pressure to be expected from that change in the ratio of sodium to potassium in younger people with normal blood pressure.5 The study was probably underpowered to detect such a difference. The modest rise in the anxiety score at one month (not sustained at six months) with low sodium salt is difficult to interpret since the trial was not double blind.
The outcome of this trial could have been predicted by a scrupulous examination of the study design. An opportunity to provide useful information has been missed.
Competing interests: None declared.
References
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