Elsevier

Nutrition

Volume 21, Issue 4, April 2005, Pages 462-466
Nutrition

Applied nutritional investigations
Does dietary recall adequately assess sodium, potassium, and calcium intake in hypertensive patients?

https://doi.org/10.1016/j.nut.2004.08.021Get rights and content

Abstract

Objective

A diet low in sodium, high in potassium, and high in calcium is recommended to lower blood pressure. However, compliance with this diet is poor, probably because of dietary intake underestimation. Therefore, we compared electrolyte intake as estimated from dietary recall with a 24-h urinary excretion.

Methods

Thirty-six patients (26 men and 10 women) with a mean age of 46 ± 8 y participated in the study. All participants had essential hypertension and were on no drug therapy (n = 20) or non-diuretic monotherapy (n = 16). Patients were instructed to consume a low-sodium (50 mmol/d), high-potassium (supplementation with 30 to 60 mmol/d), and high-calcium (1000 mg/d) diet. Compliance with the diet was assessed at baseline and then 1, 2, and 3 mo after starting the diet. Sodium, potassium, and calcium intakes were carefully estimated from patients’ dietary recall and 24-h urinary collection.

Results

Estimated sodium intake significantly correlated with 24-h urinary excretion (R = 0.43 P < 0.001). However, estimated sodium intake was lower than urinary sodium excretion by 34% at baseline and by 47% after 3 mo of dieting (P < 0.05). Estimated potassium intake correlated with 24-h urinary excretion. Estimated calcium intake significantly increased from 933 ± 83 mg/d to 1029 ± 171 mg/d (P < 0.05). Calcium intake derived from patients’ recall far exceeded and only slightly correlated with 24-h urinary excretion (R = 0.23, P < 0.01).

Conclusions

Patients tend to underestimate their sodium intake by 30% to 50%; therefore, urinary sodium excretion is more accurate to assess sodium intake. Thus, 24-h urinary sodium excretion should be used in clinical practice and in clinical trials, especially when dietary non-compliance is suspected.

Introduction

Nutritional sodium, potassium, and calcium are considered regulators of blood pressure (BP) [1]. There is considerable evidence relating sodium intake to BP. Analysis of the International Cooperative Study on the relation of Sodium and Potassium to Blood Pressure (INTERSALT), which included more than 10 000 subjects, showed a highly significant relation between salt intake and BP [2]. Controlled clinical trials such as the Trial of Nonpharmacologic Intervention in the Elderly (TONE) and the Dietary Approaches to Stop Hypertension-Sodium trials have repeatedly demonstrated that low-sodium intake significantly decreases BP [3], [4]. Salt restriction is therefore a primary goal in all patients with hypertension and especially in those who are sensitive to salt.

Increased sodium intake is associated with increased BP, whereas increased potassium and calcium intake may slightly decrease BP [5]. Therefore, the assessment of the exact intake of these electrolytes in patients with hypertension is of major clinical importance.

The exact intake cannot be measured precisely but can be extrapolated from dietary recall questionnaires or 24-h urine collection under stable conditions [6]. Previous studies have reported a strong positive association between dietary intake as assessed from patients’ food recall and urinary excretion of sodium, potassium, and calcium [6], [7], [8], [9], [10], [11]. However, recent studies have shown that dietary recall underestimates sodium and potassium intakes [12], [13]. We evaluated these two methods of electrolyte intake assessment in a group of patients who had hypertension and were enrolled to maintain a diet low in sodium and high in potassium and calcium.

The aim of the present study was to correlate these two modes of measurement to provide a better estimation of how much dietary recall reflects real electrolyte intake.

Section snippets

Patients

Thirty-six patients (26 men and 10 women, 24 to 67 y of age, mean age 46 ± 8 y) from our outpatient clinic participated in the study. All participants had essential hypertension and were on no drug therapy (n = 20) or monotherapy (n = 16). Patients treated with diuretics were excluded from the study as were all patients with secondary hypertension, ischemic heart disease, congestive heart failure, renal failure (creatinine > 1.5 mg/dL), and controlled diabetes mellitus. Patients were included

Patients’ characteristics

Thirty-six patients participated in the study. Most patients were overweight with an increased waist-to-hip ratio. Patient characteristics and baseline parameters are presented in Table 1.

Effect of dietary intervention on BP and heart rate

After 3 mo of dieting, systolic BP decreased only slightly by 2.5 mmHg (95% confidence interval = -6.5 to 1.5) and diastolic BP decreased by 0.9 mmHg (95% confidence interval = -4 to 2.2, P non-significant for both). Heart rate remained unchanged.

Effect of diet on estimated sodium intake and urinary sodium excretion

Estimated sodium intake decreased from 122 ± 12 mmol/d at

Discussion

Assessment of sodium, potassium, and calcium intakes is very important in the management of hypertension. The exact intake of these electrolytes over time generally cannot be measured precisely. It is well established that, under stable conditions, daily sodium intake almost equals daily urinary sodium excretion [15], [16]. However, collection of urine for 24 h is inconvenient and may be incomplete. Therefore, dietary recall may be an alternative to estimate sodium dietary intake [17], [18].

The

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