(PO22-19-22) Use of Toenails as a Non-invasive Method of Determining Salt Intake in Epidemiologic Studies

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Presenting Author(s)

Maryam Hashemian, MD, Ph. D.
– Assistant Professor, Utica University, Utica, New York, United States

Co-Author(s)

SE

Sareh Eghtesad
– Digestive Disease Research Institute
HP

Hossein Poustchi, M.D., Ph. D.
– Associate Professor, Digestive Disease Research Institute, Tehran University of Medical Sciences, Tehran, Tehran, Iran
AT

Adriana Torres
– Utica College
JB

John Brookman
– University of Missouri Columbia
AE

Arash Etemadi, M.D., Ph.D.
– National Cancer Institute, Division of Cancer Epidemiology and Genetics, Rockville, Maryland, United States
SD

Sandford Dawsey
– National Cancer Institute
AH

Azita Hekmatdoost
– Shahid Beheshti University of Medical Sciences
FK

Farin Kamangar
– Morgan State University
RM

Reza Malekzadeh, M.D.
– Distinguished Professor, Digestive Disease Research Institute, Tehran University of Medical Sciences, Tehran, Tehran, Iran
CA

Christian Abnet
– National Cancer Institute

Disclosure(s):

Maryam Hashemian, MD, Ph. D.: No relevant financial relationship(s) with ineligible companies to disclose.

Objectives: The currently recommended method for assessing salt intake is a 24-hour urine sodium excretion which is not feasible in large epidemiologic studies. This study aimed to investigate the validity of measuring sodium in toenails, as a novel feasible method, against 24-hour urine (24HR) samples collected in the PERSIAN Cohort.

Methods: We recruited 176 individuals, aged 35-70, and obtained 24HR urine samples every three months for a year and toenail samples at the end of the study. The concentrations of sodium were determined by flame photometry in urine samples and by instrumental neutron activation analysis in toenail samples. Toenails were washed with 10% nitric acid before measurement. The mean of the four 24HR (m24HR) urine samples was used for validation. A Spearman correlation test was conducted to assess agreement between the 24HR urine samples and the toenail samples. A questionnaire asking about the frequency of bathing, swimming, or washing feet, and the time between the last wash/bath/swim and toenail clipping was filled out at the time of toenail collection.

Results: Toenails and 24HR urine samples were provided by 111 and 130 participants, respectively but in 43 participants the volumes of 24HR urine samples were not reported. The median concentration of sodium in the toenail samples was 325.8 (235.4-479.3) µg/g and in the m24HR samples was 1067.2 (1294.6-2305.2) mg/d. Twenty-one percent, 1%, and 78% of participants reported daily bathing, swimming, and washing of their feet, respectively. The mass of nail samples and foot washing frequency were correlated with sodium concentrations in the toenails (r=0.34 and -0.41 respectively). The correlation coefficient between sodium concentrations in toenails and m24HRs was 0.12 (p=0.3). However, by excluding the participants who reported more than one time per day washing their feet (n=21), the coefficient became 0.22 (p=0.13), and by excluding the participants who reported bathing or washing their feet every day (n=32), the coefficient became 0.50 (p=0.04).

Conclusions: Our results show sodium may leak out during frequent foot washing and do not support the usage of toenails as a biomarker for sodium intake.

Funding Sources: The Intramural Program of the US National Cancer Institute (NIH) and Tehran University of Medical Sciences