Susan Jeffrey

December 05, 2013

DALLAS, Texas — Results of a randomized trial with the aim of reducing sodium intake on a population level show that an intervention that included subsidizing the purchase of a salt substitute reduced 24-hour sodium excretion, although effects on blood pressure were not significant.

Findings from the China Rural Health Initiative - Sodium Reduction Study were presented here at the American Heart Association (AHA) 2013 Scientific Sessions.

"We identified a low-cost, practical intervention that was effective in reducing sodium intake," lead author Nicole Li, PhD, The George Institute for Global Health, Sydney, Australia, concluded in a statement.

"The effects appear to have been driven primarily by the use of salt substitute, through the provision of relevant health education and access to salt substitute purchase," Dr. Li told attendees here. This subsidization was important for uptake, she added, "and salt substitution has significant potential to reduce the large burden of blood pressure-related diseases in rural China."

The study was funded by the National Heart, Lung, and Blood Institute; the Centers for Disease Control and Prevention; and the United Health Group Chronic Disease Initiative.

Important Modifiable Risk Factor

Excessive sodium intake has been identified as an important modifiable risk factor for cardiovascular disease, the leading cause of death in China, Dr. Li said. The World Health Organization and other groups see population-based approaches to salt reduction as among the most cost-effective ways to prevent vascular disease in both developed and developing countries, the authors note.

"Strokes, high blood pressure, and excess salt consumption ranging from 12 to 15 grams a day are highly prevalent in rural China," she said, a level at which there "is very little debate" about the adverse effects or potential benefit of salt restriction.

The study presented here was a large-scale, cluster-randomized trial in 5 Northern Chinese provinces. Two counties were selected from each province, and 12 townships enrolled from each county for a total of 120 clusters. One village was then selected from each township and randomly assigned to receive the community-based intervention or to act as a control, continuing with usual practice.

The intervention included a health education program delivered by community health educators, with the assistance of village leaders and volunteers, underlining the salt reduction message and providing information about the risks of high salt consumption and ways to reduce salt intake.

The second component of the intervention was provision of a reduced-sodium, added-potassium salt substitute. Villages in the intervention group were further randomly assigned to receive additional subsidies toward purchase of the salt substitute that cut the price differential with normal salt — which is about half the cost of salt substitute — or alternatively to have access but no subsidy.

The researchers targeted individuals at high risk for cardiovascular disease; those having a self-reported history of heart disease, stroke, or diabetes; those having a measured systolic blood pressure of 160 mm Hg or higher; and those having a self-reported history of a systolic blood pressure measure at that level after 50 years of age in the past.

The intervention was implemented for 18 months. The primary outcome was 24-hour urinary sodium from a random sample of 2400 men and women (20 from each village) stratified by age and sex. Secondary outcomes included the mean 24-hour urinary potassium excretion, mean ratio of 24-hour urinary sodium-to-potassium ratio, participants' knowledge and practices relating to salt and salt substitute, mean systolic and diastolic blood pressures, and the proportion of individuals with hypertension.

In the control villages, the average urinary sodium was 243 mmol/d or roughly 14 g of salt per day, Dr. Li said. "In the intervention villages, we have achieved a 13-mmol reduction of sodium excretion," she said, along with a 7-mmol increase in urinary potassium. There was no significant difference seen at this point in blood pressures, although the authors note that their study had limited power for secondary blood pressure and hypertension outcomes.

Table. Primary and Secondary Outcomes by Group

Endpoint Intervention Group Control Group Difference (95% Confidence Interval) P Value
Urinary sodium (mmol/d) 230 ± 99 243 ± 96 –13 (–26 to –1) .03
Urinary potassium (mmol/d) 51 ± 26 44 ± 19 7 (4 to 10) <.001
Urinary sodium-to-potassium ratio 5.2 ± 3.1 6.1 ± 2.6 –0.9 (–1.2 to –0.5) <.001
Systolic blood pressure (mmHg) 141 ± 22 142 ± 22 –1.0 (–3.2 to 1.2) .39
Diastolic blood pressure (mmHg) 86 ± 13 86 ± 14 –0.8 (–2.3 to 0.8) .34
Prevalence of hypertension (%) 56 58 –2.2 (–5.5 to 1.2) .20

There were also a significant increase in knowledge and positive behaviors related to salt use, including knowing that the daily limit of sodium should be less than 6 g of salt per day, and an increase in the use of salt substitute in intervention villages (62% vs 6%; P < .001).

Important to uptake of the salt substitute, though, was the price subsidy. In the villages where there was a subsidy, 79% of the study households were using the salt substitute vs 44% of households in the villages where no subsidy was offered (P < .001).

Previous work has suggested that a 1-g reduction in salt intake delivers a 1.8% to 2.8% reduction in stroke, Dr. Li noted. The reduction of 13 mmol or 0.75 g achieved in this study could prevent between 28,000 and 42,000 strokes each year in China, not counting potential benefits of potassium supplementation, Dr. Li concluded.

Important First Step

Invited discussant for this presentation here was Mikhail N. Kosiborod, MD, St. Luke's Health System, Kansas City, Missouri. He pointed out that despite the statistically significant but "modest" reduction in sodium excretion, there was no difference in blood pressure between the groups.

He speculated that the very slight reduction seen in sodium intake may relate to a change in how Chinese people are getting their sodium.

"Studies in the West show that only 11% of dietary sodium comes from table salt and cooking, and close to 80% comes from processed foods," he said. "That has not traditionally been the case in China, particularly in rural China; however, one of the questions is whether urbanization might have impacted sources of dietary sodium in rural China." If it did, that might have affected outcomes in this intervention study, Dr. Kosiborod said.

The most important question is whether strategies such as this will lead to effective reduction in hypertension as well as related events, he concluded. "Programs like this clearly are an important first step, but given the modest reduction in sodium intake demonstrated, it will likely need to be combined with other additional interventions to reduce dietary sodium and improve blood pressure control."

The study was funded by the National Heart, Lung, and Blood Institute; the Centers for Disease Control and Prevention; and the United Health Group Chronic Disease Initiative. The authors have disclosed no relevant financial relationships. Dr. Kosiborod reports having received honoraria from Genentech; serving as a consultant/advisory board member for Gilead Sciences, Genentech, Medtronic Minimed, Hoffman La Roche, AstraZeneca, Abbvie; and having received research grants from Gilead Sciences, Genentech, Medtronic Minimed, Glumetrics, Sanofi-Aventis, Maquet, and the American Heart Association.

American Heart Association (AHA) 2013 Scientific Sessions. Abstract #LBCT.02. Presented November 18, 2013.

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