Self-monitoring device useful for guiding salt intake reduction
A simple self-monitoring device effectively reduces daily salt intake and systolic blood pressure (SBP), as shown in a study.
Developed in Japan, the self-monitoring device consists of a 1-litre urine cup and an electrical apparatus with volume and conductivity sensors. It estimates salt intake by analysing data from overnight urine using a preinstalled calculation formula.
Since the conductivity sensor measurement can be overestimated by other electrolytes, such as potassium, the sodium chloride concentration was measured and then adjusted using a correlation formula as the value between the values obtained with the ion electrode method and the conductivity method.
The investigators pointed out that although the resulting daily salt intake value could be less accurate than other evaluation methods used in hospitals, the device is convenient and can be performed by patients themselves at home.
In the study, 158 adults were randomly assigned to either the intervention (n=79; mean age 61 years; 68.4 percent female) or the control (n=79; mean age 63.9 years; 64.6 percent female) group. Participants in both groups received lectures about salt reduction, but only the intervention group used the self-monitoring device to estimate their daily salt intake.
The primary outcome of change in mean daily salt intake from baseline, as measured by spot urine, after 4 weeks was greater in the intervention group (from 9.04 to 8.60 g/day) than in the control group (from 9.37 to 8.97 g/day). Relative to nonuse, the use of the device was associated with a mean salt intake reduction of 0.50 g/day (95 percent CI, −0.95 to −0.05; p=0.030). [Hypertens Res 2018;41:524-530]
Additionally, the intervention group showed a greater decline in SBP (difference, −4.4 mm Hg; −8.7 to −0.1; p=0.044) but not in DBP (difference, −0.5 mm Hg; −4.2 to −3.2; p=0.793).
There was no significant correlation between the difference in daily salt intake estimated by the spot urine method and the difference in BP (p=0.94 for SBP and p=0.99 for DBP). The absence of association could be explained by the fact that the values estimated by spot urine reflect only 1-day and not longer-term salt intake, according to the investigators.
“In addition, it is possible that participants in the intervention group gained a high awareness of BP control by using the device and changed their behaviour through exercise, diet, medication or other means,” they continued. “If such behaviour change did occur, it could be regarded as an indirect effect of using the device.”
“To the best of our knowledge, this is the first randomized controlled trial to investigate the effects of a simple device for self-monitoring of daily salt intake on salt reduction,” the investigators said.
Despite the presence of several study limitations, the present data show that the device, as recommended by The Japanese Society of Hypertension, represents a useful tool for salt reduction, they added.