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Nitric Oxide. 2015 May 1;47:65-76. doi: 10.1016/j.niox.2015.04.002. Epub 2015 Apr 15.

Is dietary nitrate/nitrite exposure a risk factor for development of thyroid abnormality? A systematic review and meta-analysis.

Author information

1
Nutrition and Endocrine Research Center, Obesity Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
2
Department of Clinical Nutrition and Dietetics, Faculty of Nutrition Sciences and Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
3
Endocrine Physiology Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran; Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Electronic address: Ghasemi@endocrine.ac.ir.
4
Minimally Invasive Surgery Research Center; Iran University of Medical Sciences, Tehran, Iran; Department of Epidemiology, School of Public Health, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
5
Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
6
Prevention of Metabolic Disorders Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.

Abstract

The potential effects of inorganic nitrate/nitrite on global health are a much debated issue. In addition to possible methemoglobinemia and carcinogenic properties, anti-thyroid effects of nitrate/nitrite have been suggested. Considering the growing significance of nitrate/nitrite and since there is no comprehensive review in data available, clarifying the effect of nitrate/nitrite on thyroid disorder outcomes is essential. Therefore, we conducted this systematic review of experimental and clinical studies, and a meta-analysis of relevant cohort and cross-sectional studies investigating the association of nitrate/nitrite exposure and thyroid function. Most animal studies show that high exposure (~10-600 times of acceptable daily intake) to nitrate/nitrite induces anti-thyroid effects, including decreased serum level of thyroid hormones and histomorphological changes in thyroid gland; however no similar observations have been documented in humans. Based on our meta-analysis, no significant association was observed between nitrate exposure and the risk of thyroid cancer, hyper- and hypothyroidism; findings from three cohort studies however showed a significant association between higher exposure to nitrite and the risk of thyroid cancer (risk = 1.48, 95% confidence interval = 1.09-2.02, P = 0.012). Additional research is needed to clarify the association between nitrate/nitrite exposures and both thyroid function and cancer.

KEYWORDS:

Goiter; Nitrate; Nitrite; Thyroid cancer; Thyroid function

PMID:
25889269
DOI:
10.1016/j.niox.2015.04.002
[Indexed for MEDLINE]

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