Reliable Quantification of the Potential for Equations Based on Spot Urine Samples to Estimate Population Salt Intake: Protocol for a Systematic Review and Meta-Analysis

Background

Methods based on spot urine samples (a single sample at one time-point) have been identified as a possible alternative approach to 24-hour urine samples for determining mean population salt intake.

Objective

The aim of this study is to identify a reliable method for estimating mean population salt intake from spot urine samples. This will be done by comparing the performance of existing equations against one other and against estimates derived from 24-hour urine samples. The effects of factors such as ethnicity, sex, age, body mass index, antihypertensive drug use, health status, and timing of spot urine collection will be explored. The capacity of spot urine samples to measure change in salt intake over time will also be determined. Finally, we aim to develop a novel equation (or equations) that performs better than existing equations to estimate mean population salt intake.

Methods

A systematic review and meta-analysis of individual participant data will be conducted. A search has been conducted to identify human studies that report salt (or sodium) excretion based upon 24-hour urine samples and spot urine samples. There were no restrictions on language, study sample size, or characteristics of the study population. MEDLINE via OvidSP (1946-present), Premedline via OvidSP, EMBASE, Global Health via OvidSP (1910-present), and the Cochrane Library were searched, and two reviewers identified eligible studies. The authors of these studies will be invited to contribute data according to a standard format. Individual participant records will be compiled and a series of analyses will be completed to: (1) compare existing equations for estimating 24-hour salt intake from spot urine samples with 24-hour urine samples, and assess the degree of bias according to key demographic and clinical characteristics; (2) assess the reliability of using spot urine samples to measure population changes in salt intake overtime; and (3) develop a novel equation that performs better than existing equations to estimate mean population salt intake.

Results

The search strategy identified 538 records; 100 records were obtained for review in full text and 73 have been confirmed as eligible. In addition, 68 abstracts were identified, some of which may contain data eligible for inclusion. Individual participant data will be requested from the authors of eligible studies.

Conclusions

Many equations for estimating salt intake from spot urine samples have been developed and validated, although most have been studied in very specific settings. This meta-analysis of individual participant data will enable a much broader understanding of the capacity for spot urine samples to estimate population salt intake.

Developing a national salt reduction strategy for Mongolia

BACKGROUND

The increase in prevalence of risk factors such as hypertension has contributed to an incremental rise in non-communicable diseases (NCDs) in Mongolia over recent decades, such that they now account for 80% of all deaths in the country. Salt reduction is one of the most cost-effective interventions to reduce the burden of NCDs.

METHODS

In 2011, the Ministry of Health (MOH) instigated the development of a national salt reduction strategy for Mongolia. As part of a 2-week national consultation and training program on salt reduction, it established an inter-sectoral working party and organized a series of bilateral meetings and visits to factories. Actions arising included a baseline survey of population salt consumption patterns and the implementation of a series of pilot salt reduction initiatives.

RESULTS

The results of the baseline assessment revealed that average daily intake of salt, based on 24 hour urine samples from a representative national sample (n=1,027), was 11.06±5.99 g in 2011, more than double the World Health Organization (WHO) five grams recommendation. Moreover, while most participants knew that salt was bad for health, few were taking efforts to reduce intake, and many were consuming highly salty meals and tea; salt in tea alone was estimated to contribute 30% of daily salt intake. A pilot Pinch Salt intervention to reduce salt consumption of factory workers was undertaken in Ulaanbaatar (UB) city between 2012 and 2013, and was associated with a reduction of 2.8 g of salt intake. Ongoing food industry initiatives have led to significant reductions in salt levels in bread, and companies producing processed meat have indicated a willingness to reduce salt. Relevant stakeholders have also supported the campaign by participating in annual World Salt Awareness Week events. The activities to date have demonstrated the potential for action and there is now a need scale these up to a national level to ensure that Mongolia is in a strong position to achieve a 30% reduction in population salt intake by 2025. The main goal of the Mongolian national salt reduction strategy is to create a social, economic and legal environment that supports salt reduction, including by influencing food supply, increasing partnerships between government and relevant stakeholders, and creating an enabling environment to support improved consumer choices. The strategy will be implemented from 2015 to 2025, with an interim review of progress in 2020.

CONCLUSIONS

Given that Mongolia has one of the highest rates of stroke in the world, which is strongly associated with population-wide blood pressure (BP) levels, the addition of a population-based stroke surveillance program would provide a reliable direct assessment of the impact of these salt reduction initiatives on the health of the Mongolian people. The results from this research would likely be widely generalizable to other populations experiencing similar lifestyle transitional changes.