Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 51 4 2022 04 14 839 850 Dariush D. Farhud 1. School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2. Department of Basic Sciences/Ethics, Iranian Academy of Medical Sciences, Tehran, Iran 3. Farhud Genetic Clinic, Tehran, Iran Marjan Zarif-Yeganeh 1. Farhud Genetic Clinic, Tehran, Iran 2. Cellular and Molecular Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran Atefeh Mehrabi Farhud Genetic Clinic, Tehran, Iran Ali-Reza Afshari Pediatric Gastroenterology and Hepatology Research Center, Zabol University of Medical Sciences, Zabol, Iran Mohammad Bagher Rokni School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Keyvan Majidi Noor Pathobiology Laboratory, Tehran, Iran Maryam Jalali Noor Pathobiology Laboratory, Tehran, Iran Ali Akbar Amir Zargar Noor Pathobiology Laboratory, Tehran, Iran AND Department of Immunology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Abdolfattah Sarafnejad 1. Noor Pathobiology Laboratory, Tehran, Iran 2. Department of Immunology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Hamid Reza Sadeghipour 1. Noor Pathobiology Laboratory, Tehran, Iran 2. Department of Physiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Shaghayegh Zokaei Farhud Genetic Clinic, Tehran, Iran Farideh Khosravi 1. Noor Pathobiology Laboratory, Tehran, Iran 2. Department of Immunology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Mahmoud Jalali 1. Noor Pathobiology Laboratory, Tehran, Iran 2. Department of Biochemistry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Mohammad Khazeni Department of Virology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2022 04 14 Background: Calcium is a necessary mineral for life to keep the body and bones healthy. Various factors including hormones, diet, age, and gender affect serum calcium status. The aim of this sturdy was to assess the serum calcium level (SCL) of Tehran population, which has about 10 million multi-Ethnic populations and represents from the whole country. Methods: In this retrospective study, the measured SCL of 105,128 individuals referred to different laboratories of Tehran, Iran were evaluated and its relationship with the age, gender, seasons, and different years during 2009-2018, were analyzed. Results: After excluding outliers, 91,257samples remained, which 61162 (58.64%) and 30,095 (41.36%) were female and male, respectively.  The mean SCL was 9.36 (9.35, 9.37) mg/dl (95%CI). The highest and lowest SCLs were 3.1 and 18.2mg/dl, respectively. From the total study population, 74127 (81.23%) had normal SCLs, 14110 (15.46%) had hypocalcemia, and 3020 (3.31%) had hypercalcemia. SCLs were normal in 83.6% of men and 79.66% of women. Women had a significantly higher frequency of hypocalcemia compared to men (17.2% vs. 12.83%, p<0.0001). Conclusion: Normal and abnormal SCLs were significantly different in age groups and in both genders. It means that gender and age affect SCLs. Every year of increasing age, reduces the chance of hypercalcemia by 40%, significantly. Age seems to affect hypercalcemia more than hypocalcemia. Age in men increases the risk of hypocalcemia, and reduces the risk of hypocalcemia in women. Therefore, it is recommended to encourage dietary calcium intake among premenopausal women and older men. https://ijph.tums.ac.ir/index.php/ijph/article/view/28446 https://ijph.tums.ac.ir/index.php/ijph/article/download/28446/7567