https://orcid.org/0000-0003-0029-1189
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Abstract
People with obesity have been found to have lower zinc (Zn) and selenium (Se) circulatory levels and abnormal thyroid function than people with normal weight. Studies about the effects of Zn and Se supplementation on body composition and thyroid function of overweight-obese people showed inconsistent results. A systematic review of randomized controlled trials was conducted to determine the effects of Ζn supplementation, Se supplementation, and their combination on body composition and thyroid function of individuals with overweight or obesity. Databases of PubMed, ScienceDirect, and Cochrane, were searched from inception to February 27, 2022, to identify relevant articles. For the assessment of the methodological quality of the studies, the Jadad scale was used. After screening the articles, thirteen studies were finally included and were analyzed using the strength of the evidence approach. Regarding the effectiveness of Zn supplementation on body composition, moderate evidence was found, while the effects of Se were found to be mixed. Zn supplementation was found to affect the thyroid function of people with overweight or obesity by increasing their free triiodothyronine (FT3) levels. However, this result is based only on one study among hypothyroid patients. At this point, the effectiveness of Zn, Se, and their combination, on the body composition and the thyroid function of people with overweight or obesity cannot safely be determined because of the controversial results, small number, and the limitations of the identified studies. The results of this systematic review must be interpreted with caution due to the limitations detected.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The author(s) reported there is no funding associated with the work featured in this article.
Author contributions
Conceptualization, A.Z., E.A, G.A., Z.R, and C.G.; methodology, A.Z, and E.A; validation, A.Z. and E.A.; investigation, A.Z.; data curation, A.Z., and E.A.; writing—original draft preparation, A.Z.; writing—review and editing, E.A., G.A. Z.R and C.G.; supervision, C.G., and E.A.; All authors have read and agreed to the published version of the manuscript.
Additional information
Notes on contributors
Antonis Zavros
Antonis Zavros is a Ph.D. candidate at the Department of Life and Health Sciences of the University of Nicosia, Cyprus. He holds a BSc degree in Sports Science and Physical Education from the Aristotle University of Thessaloniki, Greece, an MSc degree in Exercise Fitness and Health from the University of Nicosia, Cyprus, and an MSc degree in Applied Nutrition and Dietetics from the European University of Cyprus. Antonis Zavros has been awarded a Ph.D. scholarship by the Cyprus National Scholarships Foundation for his academic achievements. His research interests focus on the effects of nutritional supplements and high-intensity functional training on the metabolism, thyroid function, exercise performance, and body composition in overweight-obese people.
Christoforos D. Giannaki
Dr. Christoforos D. Giannaki is an Associate Professor in the Department of Life and Health Sciences of the University of Nicosia, Cyprus, and the coordinator of the Ph.D. program in Exercise Science and Physical Education. He holds a BSc Degree in Physical Education and Sports Science from the University of Thessaly, Greece, an MSc Degree in Sports Physiology from Liverpool John Moores University, United Kingdom, and a Ph.D. from the School of Medicine, University of Thessaly, Greece. Dr. Giannaki has published a number of research articles in international scientific peer-reviewed journals, and he is a member of international health and medical-related bodies. His research interests are focused in the area of exercise and health physiology and exercise, nutrition and sleep.
George Aphamis
Dr. George Aphamis is an Assistant Professor in Exercise Physiology at the University of Nicosia, Cyprus. Following his studies in Sports Science at the University of Athens, Greece (1997), he studied Exercise Physiology at the graduate level at McGill University, Montreal, Canada (2000). He then pursued doctoral studies at Loughborough University, Loughborough, UK, graduating with a Ph.D. in Exercise Physiology (2011). Dr. Aphamis is involved in several projects on nutrition and sports performance, exercise, and health. His research work has been presented at international conferences and published in peer-reviewed journals.
Zoe Roupa
Dr. Zoe Roupa is a Professor in the Department of Life and Health Sciences of the University of Nicosia, Cyprus, a medical doctor, and a nurse. She has published more than a hundred peer-reviewed articles, and her work has been cited more than 243 times by other scientists. In addition, Dr. Zoe Roupa is the coordinator of two MSc nursing programs at the University of Nicosia, Cyprus, and she has supervised more than 90 theses.
Eleni Andreou
Dr. Eleni Andreou is an Associate Professor in Nutrition-Dietetics at the University of Nicosia, Cyprus. She is also the President of the Cyprus Dietetic and Nutrition Association, the President of the Cyprus Society Parenteral, Enteral Nutrition, and the Vice President of the Cyprus Registration Board for Food Scientists, Technologists, and Dietitians. She has published a number of peer-reviewed papers and has organized and participated in numerous local and international conferences as an invited speaker. Her research interests are focused on Behavioral Modification, Diabetes, Obesity, Eating Disorders, and Cognition-sleep and Nutrition.