Dietary Salt Restriction: How Much Education Is Enough?

The appreciation of salt's effect on the blood pressure (BP) of most individuals has been observed and extensively documented in medical literature through observational studies1, 2 and systematic reviews.3, 4 High salt intake is independently associated with hypertensive target organ damage5 and excess weight aggravates the tendency of high salt intake to elevated BP.6 In an attempt to implement these findings, nearly every organizational recommendation for BP management begins with dietary education.7-9 Currently, the World Hypertension League has established nomenclature standardizing categories of salt intake and also proposed ranges of reduction for clinical and population interventions.10 If the dietary salt education recommended by these guidelines is employed, then many hypertensive patients should be aware that dietary salt reduction could lower their BP and potentially reduce their medication burden. However, in many instances, even salt-conscious individuals are not as conscious as they think, when urinary sodium excretion is used as a guide to evaluate their sodium intake.11 Therefore, the difficulty remains: how can we best deliver an implementable plan for salt reduction to our patients in a clinical setting? In this issue of the Journal of Clinical Hypertension, Nakano and colleagues12 tested the hypothesis that using regularly scheduled, 20-minute educational sessions with nutritionists directed at developing individualized plans for salt restriction could lower urinary sodium excretion, ambulatory BP monitoring (ABPM), and clinic BP. Their findings support that, at least in a relatively short-term period, nutritionist-directed education and support can be effective for a small population in lowering both ABPM and clinic BP. In a relatively straightforward designed study, Nakano and colleagues randomized 95 hypertensive patients to conventional salt education from their provider or a nutritional education group. The conventional salt education group received a “brief explanation of the causes and consequences of a high-salt diet” from their provider. In contrast, the nutritionist education group received five sessions that generally lasted greater than 20 minutes with nationally certified nutritionists. Importantly, the nutritionist-led direction given to the participants in the study group was individualized to the participant based on his or her response to the Food Frequency Questionnaire and a salt preference survey. In other words, the nutritionists took the time to learn the specific dietary pitfalls of these participants and then developed salt-limiting dietary plans unique to each participant. Their results were not surprising. As expected, the nutritionist education group had a statistically significant reduction most prominently noted in the 24-hour ABPM where a 5/2 mm Hg BP reduction was noted. In addition, other office and home BP measurements tended to be lower in the nutritionist education group. These findings correlated appropriately with the 24-hour urinary sodium excretion reduction found in the intensely educated group. However, a closer look at Nakano and colleagues’ findings may highlight some of the difficulties clinicians and patients face in dealing with the dietary salt problem. The most glaring clinically encountered obstacle is the time and resource commitment necessary to implement this intervention. The nutritionist-educated participants visited with their nutritionist five times over a 12-week period for what may seem at first glance to be only a modest reduction in BP. Would typical patients consider it worth all the effort, perhaps the missed work or travel resources, to invest in sessions such as these only to have less BP benefit than a single pill might deliver? Here again, the individualized approach is important to consider. For some patients, limited by factors mentioned above, they may decide that they cannot honor that commitment. For others, however, these visits to a nutritionist might be viewed as many patients view physical therapy—as an intermittent and necessary treatment routine to empower the individual and develop good, long-term habits. Could it be physical therapy for the diet? Highlighting the long-term benefits of nonpharmacologic BP control as an adjunct to pharmacologic measures13 might be necessary for many providers to enlist their patients’ cooperation in such an intervention. It is, however, the long-term benefit that this paper cannot sufficiently address and remains a valid question. The authors admit that at a 6-month interval following the conclusion of the study, the nutritionist-educated group had lost its statistically significant BP reduction as a whole, although approximately 20% of the participants continued to have significantly lower BP. This finding begs the question, “How much dietary intervention is enough?” The authors postulate that less-frequent nutritionist follow-up visits (eg, every 6 months) might be necessary to continue to see this BP benefit. This remains unknown. In addition, even though benefit was seen for the intervention group as a whole, more than half (55%) of the participants in the intervention group did not attain the target sodium restriction of <6 g/d. Yet, those participants who did achieve the desired degree of sodium reduction achieved an even more robust systolic BP reduction when measured with 24-hour ABPM (−8.3±1.8 mm Hg vs −1.3±1.6 mm Hg). This finding serves as both bad news and good news. It highlights the difficulty in achieving a low-salt diet, even with a more intense intervention, but it also underscores the benefit of systolic BP reduction when that low-salt diet is achieved. Again, the question remains, “How much dietary intervention is enough?” A final clinical difficulty in the authors’ findings is the isolation of participants for whom the intense salt-lowering education made little difference—patients taking diuretics. This population in Western countries represents a much higher percentage of hypertensive patients than it did in this particular study, thereby, perhaps, limiting the population benefit of such a strategy as outlined by the authors. Conceptually, this also suggests that the final common denominator of both strategies is salt balance: either by reducing intake or hastening excretion with diuretic medications. Multiphase bioimpedance is a cost-effective and reproducible technology to deliver this assessment extracullular and intracellular water space(s) immediately to the office, including in response to antihypertensive and diuretic therapy.14 It would be interesting to investigate the monitoring of efficacy of salt restriction with bioimpedance in future studies. In addition, timed urine collections are notorious for potential inaccuracy of collection. In this study, a formal assessment for completeness of urine collection (eg, with per os para-aminobenzoic acid15) was not performed. In summary, in contrast to previous studies that have analyzed the benefit of low-salt diets on BP reduction,16 Nakano and colleagues have shown that patients can be empowered by education, and, at least for some, benefit in BP reduction can be attained. Perhaps not all patients need a prescriptive low-salt diet to reduce their BP; however, if clinicians enlist the help of knowledgeable nutritionists who can develop individualized plans to educate hypertensive patients, vested patients may be able to work with providers in lowering their BP by putting into practice their education. It appears from this research that individualized patient education has not lost its place in the patient-centered algorithm of hypertension treatment. The question remains, “How much education is enough?” Nakano and colleagues have pushed that question back to the forefront.