Dietary Sodium 'Controversy'-Issues and Potential Solutions

PURPOSE OF REVIEW

High dietary sodium is estimated to be the leading dietary risk for death attributed to 1.8 million deaths in 2019. There are uniform recommendations to reduce sodium consumption based on evidence that increased dietary sodium is responsible for approximately a third of the prevalence of hypertension, and meta-analyses of randomized controlled trials show that sodium reduction lowers blood pressure, cardiovascular disease, and total mortality. Nevertheless, there is a perception that the beneficial effect of reducing dietary sodium is controversial. We provide experiential evidence relating to some sources of the controversy and propose potential solutions.

RECENT FINDINGS

Inappropriate research methodology, lack of rigor in research, conflicts of interest and commercial bias, questions of professional conduct, and lack of policies to protect public interests are likely to contribute to the controversy about reducing dietary sodium. There is a failure to protect policies to reduce dietary sodium from nonscientific threats. Significant efforts need to be made to ensure the integrity of nutritional research and maintain public trust.

Knowledge, attitude and behaviour of university students regarding salt and iodine: a multicentre cross-sectional study in six countries in Europe and Asia

Background

Strategies to reduce salt intake are encouraged to be implemented in parallel with those that aim to ensure iodine adequacy at the population level. The aim of the present study was to assess and compare knowledge, attitudes and behaviours related to salt and iodine among students in Europe and Asia.

Methods

A multicentre cross-sectional study was conducted with 2459 university students in total (42.7% males, median age 21 years) from four countries in Europe and two countries in Asia. Data were collected with the use of a self-administered questionnaire, and univariate and multivariate statistical analyses were performed to explore any association between variables.

Results

Only 6.5% of all participants knew the correct salt recommendations. Nearly a quarter of them (24.4%) found salt recommendations confusing and/or contradictory. There were significant differences between European and Asian participants, with those from Europe being better informed about salt recommendations, but significantly less knowledgeable about iodine. The reported frequency of use of salt and salt-containing sauces either at the table or for cooking, as well as knowledge about ways to reduce salt intake among those who indicated to make conscious efforts to do so, differed significantly between countries. Significant differences between countries were also observed with respect to the type of salt used, with about one third of all participants (34%) not being aware of the kind of salt they used.

Conclusion

The results of this survey highlight serious salt- and iodine-related knowledge gaps among university students in Europe and Asia. Raising awareness and conducting information campaigns is needed to promote changes in behaviour that would result in a reduction of salt intake and conscious use of iodised salt at the individual level.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13690-021-00593-5.

Left Ventricular Mass Reduction by a Low-Sodium Diet in Treated Hypertensive Patients

OBJECTIVE

To evaluate the left ventricular mass (LVM) reduction induced by dietary sodium restriction.

PATIENTS AND METHODS

A simple sodium-restricted diet was advised in 138 treated hypertensives. They had to avoid common salt loads, such as cheese and salt-preserved meat, and were switched from regular to salt-free bread. Blood pressure (BP), 24-h urinary sodium (UNaV) and LVM were recorded at baseline, after 2 months. and after 2years.

RESULTS

In 76 patients UNaV decreased in the recommended range after 2 months and remained low at 2 years. In 62 patients UNaV levels decreased after 2 months and then increased back to baseline at 2 years. Initially the two groups did not differ in terms of BP (134.3 ± 16.10 / 80.84 ± 12.23 vs.134.2 ± 16.67 / 81.55 ± 11.18 mmHg, mean ± SD), body weight (72.64 ± 15.17 vs.73.79 ± 12.69 kg), UNaV (161.0 ± 42.22 vs.158.2 ± 48.66 mEq/24 h), and LVM index (LVMI; 97.09 ± 20.42 vs.97.31 ± 18.91 g/m2). After 2years. they did not differ in terms of BP (125.3 ± 10.69 / 74.97 ± 7.67 vs.124.5 ± 9.95 / 75.21 ± 7.64 mmHg) and body weight (71.14 ± 14.29 vs.71.50 ± 11.87 kg). Significant differences were seen for UNaV (97.3 ± 23.01 vs.152.6 ± 49.96 mEq/24 h) and LVMI (86.38 ± 18.17 vs.103.1 ± 21.06 g/m2). Multiple regression analysis: UNaV directly and independently predicted LVMI variations, either as absolute values (R2 = 0.369; β = 0.611; p < 0.001), or changes from baseline to +2years. (R2 = 0.454; β = 0.677; p < 0.001). Systolic BP was a weaker predictor of LVMI (R2 = 0.369; β = 0.168; p = 0.027; R2 = 0.454; β = 0.012; p = 0.890), whereas diastolic BP was not correlated with LVMI. The prevalence of left ventricular hypertrophy decreased (29/76 to 15/76) in the first group while it increased in the less compliant patients (25/62 to 36/62; Chi2p = 0.002).

CONCLUSION

LVM seems linked to sodium consumption in patients already under proper BP control by medications.

Formulas to Estimate Dietary Sodium Intake From Spot Urine Alter Sodium-Mortality Relationship

To study the effect of formulas on the estimation of dietary sodium intake (sodium intake) and its association with mortality, we analyzed the TOHP (Trials of Hypertension Prevention) follow-up data. Sodium intake was assessed by measured 24-hour urinary sodium excretion and estimations from sodium concentration using the Kawasaki, Tanaka, and INTERSALT (International Cooperative Study on Salt, Other Factors, and Blood Pressure) formulas. We used both the average of 3 to 7 urinary measurements during the trial period and the first measurement at the beginning of each trial. Additionally, we kept sodium concentration constant to test whether the formulas were independently associated with mortality. We included 2974 individuals aged 30 to 54 years with prehypertension, not assigned to sodium intervention. During a median 24-year follow-up, 272 deaths occurred. The average measured sodium intake was 3766±1290 mg/d. All estimated values, including those with constant sodium concentration, were systematically biased with overestimation at lower levels and underestimation at higher levels. There was a significant linear association between the average measured sodium intake (ie, gold standard method) and mortality. This relationship was altered by using the estimated sodium intakes. There appeared to be a J- or U-shaped relationship for the average estimated sodium by all formulas. Despite variations in the sodium-mortality relationship among various formulas, a common pattern was that all estimated values including those with constant sodium appeared to be inversely related to mortality at lower levels of sodium intake. These results demonstrate that inaccurate estimates of sodium cannot be used in association studies, particularly as the formulas per se seem to be related to mortality independent of sodium.

The International Consortium for Quality Research on Dietary Sodium/Salt (TRUE) position statement on the use of 24-hour, spot, and short duration (<24 hours) timed urine collections to assess dietary sodium intake

The International Consortium for Quality Research on Dietary Sodium/Salt (TRUE) is a coalition of intentional and national health and scientific organizations formed because of concerns low-quality research methods were creating controversy regarding dietary salt reduction. One of the main sources of controversy is believed related to errors in estimating sodium intake with urine studies. The recommendations and positions in this manuscript were generated following a series of systematic reviews and analyses by experts in hypertension, nutrition, statistics, and dietary sodium. To assess the population's current 24-hour dietary sodium ingestion, single complete 24-hour urine samples, collected over a series of days from a representative population sample, were recommended. To accurately estimate usual dietary sodium at the individual level, at least 3 non-consecutive complete 24-hour urine collections obtained over a series of days that reflect the usual short-term variations in dietary pattern were recommended. Multiple 24-hour urine collections over several years were recommended to estimate an individual's usual long-term sodium intake. The role of single spot or short duration timed urine collections in assessing population average sodium intake requires more research. Single or multiple spot or short duration timed urine collections are not recommended for assessing an individual's sodium intake especially in relationship to health outcomes. The recommendations should be applied by scientific review committees, granting agencies, editors and journal reviewers, investigators, policymakers, and those developing and creating dietary sodium recommendations. Low-quality research on dietary sodium/salt should not be funded, conducted, or published.