Dietary Sodium Intake and Cortisol Measurements

Angela X. Chen; Andrea V. Haas; Gordon H. Williams; Anand Vaidya

Disclosures

Clin Endocrinol. 2020;93(5):539-545. 

In This Article

Abstract and Introduction

Abstract

Objectives: To assess the influence of a dietary sodium intake intervention on cortisol measurements within the general population.

Design: Cross-over intervention.

Patients: Six hundred thirty adults without known Cushing syndrome, cardiovascular or renal disease completed a restricted dietary sodium diet (10 mmol/d, 230 mg/d) followed by cross-over to a liberalized dietary sodium diet (200 mmol/d, 4600 mg/d). Twenty-four-hour urine collection and biochemical investigations were performed at the end of each dietary intervention.

Results: Mean 24-hour urinary free cortisol increased with liberalized sodium intake when compared with restricted sodium intake (178.0 ± 89.7 vs 121.3 ± 65.6 nmol/d, P < .001). Nearly all participants (84%) had an increase in the urinary free cortisol following liberalized sodium intake. This translated to a substantial difference in the proportion of participants exceeding categorical thresholds of urinary cortisol on liberalized vs restricted sodium intake: 62% vs 27% for 138 nmol/d (50 mcg/d), 46% vs 17% for 166 nmol/d (60 mcg/d), 32% vs 10% for 193 nmol/d (70 mcg/d), 23% vs 6% for 221 nmol/d (80 mcg/d), 17% vs 4% for 248 nmol/d (90 mcg/d). In parallel, there was a small decrease in morning total serum cortisol with liberalized sodium intake (303.0 ± 117.3 vs 326.4 ± 162.5 nmol/L, P < .001).

Conclusions: Increased dietary sodium intake increases urinary free cortisol excretion and may increase the risk for false-positive results. Variations in dietary sodium intake may influence the interpretations of cortisol measurements performed to evaluate for hypercortisolism.

Introduction

The average dietary sodium intake of adults living in the United States is estimated to be 3600 mg per day.[1] This is higher than the 2019 Institute of Medicine guidelines that recommend an upper limit of 2300 mg of sodium per day in adults and substantially greater than American Heart Association guidelines, which target an upper limit of 1500 mg per day.[2,3] Higher dietary sodium intake induces a range of physiological changes including intravascular volume expansion, increased glomerular filtration rate, and suppression of renin-angiotensin-aldosterone-system (RAAS) activity.[4] Although the mean dietary sodium intake in the United States may be high, studies have consistently shown that there is large intra-individual variability in day-to-day sodium intake and excretion.[1,5,6] This variability implies that downstream physiological processes that are influenced by sodium intake may also be variable.

24-hour urinary free cortisol (24hUFC) is a screening test commonly used to assess for endogenous hypercortisolism.[7] Previous studies suggest that intra-individual variability of 24hUFC can be as high as 38%.[8] Many factors contribute to this degree of variability, including physiological fluctuations in daily cortisol secretion, inconsistent patient practice during the urine collection, physical and emotional stressors, renal impairment and more. Variability in 24hUFC for the screening of hypercortisolism can contribute to false-positive results, which may trigger more testing, healthcare expenditure and anxiety.

Although many factors affect 24hUFC, few studies have directly studied the influence of dietary factors, in particular dietary sodium intake, in the general population. The objective of the current study was to assess the influence of dietary sodium intake on 24hUFC within the general population.

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