J Epidemiol 2016;26(2):57-63 doi:10.2188/jea.JE20150037 Original Article Prevalence of Brick Tea-Type Fluorosis in the Tibet Autonomous Region Zhipeng Fan1, Yanhui Gao1, Wei Wang1, Hongqiang Gong2, Min Guo2, Shengcheng Zhao2, Xuehui Liu3, Bing Yu3, and Dianjun Sun1 1Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Key Lab of Etiology and Epidemiology, Education Bureau of Heilongjiang Province & Ministry of Health, Harbin, China 2The Institute of Endemic Disease Control, Tibet Autonomous Region Center for Disease Control and Prevention, Lhasa, China 3The Institute of Prevention and Treatment on Endemic Disease of Hulunbuir City, Zhalantun, China Received February 2, 2015; accepted June 17, 2015; released online October 24, 2015 Copyright © 2015 Zhipeng Fan et al. This is an open access article distributed under the terms of Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ABSTRACT Background: The prevalence of brick tea-type fluorosis is high in Tibet because of the habit of drinking brick tea in this region. Brick tea-type fluorosis has become an urgent public health problem in China. Methods: A cross-sectional survey was conducted to investigate prevalence of brick tea-type fluorosis in all districts of Tibet using a stratified cluster sampling method. Dental fluorosis in children aged 8–12 years and clinical skeletal fluorosis in adults were diagnosed according to the national criteria. A total of 423 children and 1320 adults participated in the study. Samples of drinking water, brick tea, brick tea infusion (or buttered tea), and urine were collected and measured for fluoride concentrations by the fluoride ion selective electrode method. Results: The fluoride level in all but one of the brick tea samples was above the national standard. The average daily fluoride intake from drinking brick tea in all seven districts in Tibet was much higher than the national standard. The prevalence of dental fluorosis was 33.57%, and the prevalence of clinical skeletal fluorosis was 46.06%. The average daily fluoride intake from drinking brick tea (r = 0.292, P < 0.05), urine fluoride concentrations in children (r = 0.134, P < 0.05), urine fluoride concentrations in adults (r = 0.162, P < 0.05), and altitude (r = 0.276, P < 0.05) were positively correlated with the prevalence of brick tea-type fluorosis. Herdsmen had the highest fluoride exposure and the most severe skeletal fluorosis. Conclusions: Brick tea-type fluorosis in Tibet is more serious than in other parts of China. The altitude and occupational factors are important risk factors for brick tea-type fluorosis. Key words: brick tea-type fluorosis; skeletal fluorosis; dental fluorosis; altitude; Tibet concentrations are higher than other types of tea. Brick tea- INTRODUCTION type fluorosis, an endemic fluorosis, is caused by consumption Approximately 99% of all fluoride retained in the human body of fluoride-containing brick tea. People can be chronically is found in mineralized tissues, mainly in bone but also in exposed to high levels of fluoride from drinking brick tea and enamel and dentin.1 Moderate levels of fluoride help to are at risk of brick tea-type fluorosis. Brick tea-type fluorosis increase bone mass and prevent dental caries. However, is characterized by mild DF in children and severe SF in exposure to high levels of fluoride can cause dental fluorosis adults. It was discovered by epidemiologic surveys in the (DF)—an undesirable developmental defect of tooth enamel 1980s among the minorities in remote western and northern during amelogenesis—and skeletal fluorosis (SF)—a condition border districts in China.6 marked by osteosclerosis and ligament calcifications and often In Tibet, the production modes of Tibetans are mainly accompanied by osteoporosis, osteomalacia, or osteopenia.2–4 agriculture and animal husbandry. Drinking brick tea or Tea leaves can store up to 98% of the fluoride present in the buttered tea, which is made of brick tea and butter, is a surrounding air and soil.5 Brick tea is made of older leaves lifestyle habit of the majority of Tibetans and can help them and stalks than other types of tea. Therefore, the fluoride digest food and ingest minerals and vitamins but also leads to Address for correspondence. Dianjun Sun, Baojian Road 157, Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin 150081, China (e-mail: [email protected]). 57 58 Prevalence of Brick Tea-Type Fluorosis in Tibet high levels of fluoride exposure.7 Furthermore, high altitude in some survey villages was less than 50. In order to ensure an could promote fluoride absorption and movement in the adequate sample size, another nearby village was chosen as a intestine, causing fluoride to be readily retained in the bone complement when less than 50 subjects were recruited from and muscle.8–10 For Tibetans, high-altitude residence might the randomly selected village. Only three villages were increase the risk of brick tea-type fluorosis. investigated in Changdu due to the long distances between The prevalence of brick tea-type fluorosis in Tibet has villages and severe weather conditions. In total, 1320 adults become an urgent public health problem in China. However, were recruited in 29 villages of seven districts, and 1227 brick most current research on the conditions associated with brick tea infusion (or buttered tea) samples and 1287 urine samples tea-type fluorosis in Tibet selected limited numbers of districts were collected. In addition, 29 drinking water samples and from Tibet and cannot adequately assess the prevalence of 107 brick tea samples, which represent generalized drinking brick tea-type fluorosis in this region. In this study, we water and brick tea exposures, were also collected. All sampled from all districts of Tibet, including Lhasa, Ali, samples were collected with a 15 mL centrifuge tube and Nagqu, Shigatse, Shannan, Linzhi, and Changdu, to stored at 4°C. investigate environmental conditions for fluoride exposure, the prevalence and severity of brick tea-type fluorosis, and Brick tea consumption disease-associated risk factors in Tibetans. We obtained information on brick tea consumption through three indices: the volume of brick tea consumed daily, the fluoride concentrations in brick tea infusion, and the average MATERIALS AND METHODS daily fluoride intake from drinking brick tea. Selection of survey villages We used a stratified random cluster sampling method for Measurement of fluoride concentrations collecting samples. Specifically, a typical county was selected Using the fluoride ion-selective electrode method (WS/T 89- from each investigation district. The towns in each county 2006), fluoride concentrations in drinking water, brick tea, were then stratified by the population size, and four towns brick tea infusion (or buttered tea), and urine samples were (both urban and rural) were selected randomly. Finally, a measured. The average daily fluoride intake from drinking village (of which there are several in each town) was brick tea was calculated using the following formula: randomly selected as a survey village from each town. Average daily fluoride intake from drinking brick tea ðmgÞ ¼ Fluoride concentration of brick tea infusion ðmg=LÞ Study population, questionnaire, and sample  ð Þ collection volume of brick tea consumed daily L DF conditions in children were investigated in the primary schools. Due to the local conditions in Tibet, there is only one Statistical analysis primary school in each town and no primary school in villages We mainly used non-parametric statistical analysis methods. of the town. Therefore, we selected the corresponding 8- to The Kruskal-Wallis H test and Nemenyi test were used to 12-year-old children belonging to the survey villages as the compare the differences in fluoride levels among districts in study population in the primary school. Baseline information Tibet. The Chi-square test was used to compare differences of the 8- to 12-year-old children was collected, including age, in the prevalence of brick tea-type fluorosis among those gender, and nationality. DF was diagnosed according to districts. Spearman’s rank correlation was used to analyze the national criteria (WS/T 208-2011). Urine samples were correlations between the average daily fluoride intake from collected using a 15 mL centrifuge tube and stored at 4°C. drinking brick tea, urine fluoride concentrations, or altitude Ultimately, we recruited 423 children and collected 416 urine and the prevalence of brick tea-type fluorosis. To examine samples. whether or not occupational factors could influence the brick Adults in the survey villages were investigated using a tea-type fluorosis, the adult participants were grouped into questionnaire, and SF was assessed and clinically diagnosed herdsmen, farmers, and other occupational groups (eg, according to national criteria (WS/T 192-2008). The workers, teachers, and students). The Kruskal-Wallis H test standard questionnaire was designed to obtain demographic and Chi-square test were used to compare the differences in information, including age, gender, nationality, income, fluoride exposure and the severity of SF among different source of drinking water, personal history of brick tea professional groups. The data were analyzed using SPSS consumption, and the volume of brick tea consumed daily. version 19.0 (IBM Corporation, Armonk, NY, USA). P values We randomly selected at least 50 subjects from each survey less than 0.05 were considered statistically significant. village. We included subjects who were aged over 16 years and who had been drinking brick tea for several years. Ethics statement However, due to different religious beliefs, geographical Following the principle of medical ethics, the investigation conditions, and personal preferences, the number of subjects and sample collection were carried out after obtaining J Epidemiol 2016;26(2):57-63 Fan Z, et al.