Dietary zinc intake, supplemental zinc intake and serum zinc levels and the prevalence of kidney stones in adults
Introduction
The prevalence of kidney stones in the United States increased from 3.2% in the period 1976–1980 to 9.8% in men and 7.7% in women in the period 2007–2012 [1,2]. The stone prevalence among adults younger than 50 years old in the United States was 6.3% in men and 6.4% in women in the period 2007–2012 [2]. Globally, calcium stones are the most common stones comprising about 80% of kidney stones [3]. In addition, the risk of kidney stone recurrence is high, and the 5-year recurrence rate of kidney stones is up to 50% [3]. Several systemic diseases and factors including obesity may lead to an increased risk of kidney stones [3]. Trace metals have been related to the development of kidney stones, among which zinc has generated the most interest [4]. Limited findings on the association between dietary zinc intake and the risk of kidney stones have been controversial. Dietary zinc intake has been found both inversely [5] and positively [6,7] associated with the risk of kidney stones, while zinc intake was not associated with the risk of kidney stones in a recent study [4]. The contradicting findings may be explained in part by the amount of zinc levels because zinc could inhibit the crystal growth even at concentrations as low as 0.1 mM/L, while it may promote the formation of amorphous calcium phosphate at higher concentrations (0.5 mM to 2 mM/L) [8,9]. However, the dose-response relationship between zinc intake and the risk of kidney stones has not been explored in epidemiological studies. In addition, the association between serum zinc levels with the risk of kidney stones has also not been reported in epidemiological studies. Furthermore, it is unclear whether the effects of dietary zinc intake and supplemental zinc intake differ on the kidney stones formation [10]. Therefore, with the hypothesis that zinc may be non-linearly associated with the risk of kidney stones, the goal of this study was to explore the dose-response relationships between dietary zinc intake, supplemental zinc intake and serum zinc levels and the prevalence of kidney stones in the 2007–2016 National Health and Nutrition Examination Surveys (NHANES).
Section snippets
Study population
NHANES is a stratified, multistage probability survey of the noninstitutionalized US population. Five consecutive NHANES 2-year cycles (2007–2008, 2009–2010, 2011–2012, 2013–2014, 2016-2016) are collected, as these cycles specifically inquired about history of kidney stones. Ethical approval is exempted.
Exposure and outcomes
The primary exposures of interest were zinc intake from diet and supplement and serum zinc levels. Two 24 -h dietary recall interviews are available for all participants. The first dietary
Results
A total of 29,199 participants responded to the question of “Have you ever had kidney stones?”. After excluding those never passing a stone (n = 314) and those who did not know if they ever had stones (n = 78), 28,807 individuals were finally included. Among the 28,807 individuals, there are 25,698 individuals providing information of dietary zinc intake, 5537 individuals providing information of supplemental zinc intake and 5088 individuals providing information of serum zinc levels. The
Discussion
To our knowledge, this is the first study to examine the dose-response relationships between dietary zinc intake, supplemental zinc intake and serum zinc levels and the risk of kidney stones in adults. Dietary zinc intake and serum zinc levels were inversely associated with the prevalence of kidney stones in adults, and there may be effect modification by participant sex and body mass index. In addition, sex contributed significantly to the variability of dietary zinc intake and serum zinc
Funding
None.
Declaration of Competing Interest
None.
Acknowledgments
The authors thank the National Center for Health Statistics of the Centers for Disease Control and Prevention for sharing the data.
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