The dose-response relationship between fluoride in brick-tea and the
prevalence of skeletal fluorosis (SF) in adults was studied to determine a safe upper limit for fluoride intake from brick-tea. In brick-tea drinking endemic fluorosis areas of the Tibetan pastoral areas of Sichuan province, cluster sampling was conducted of residents above age thirty in Amu, Jiangrong, Anqu, Longrang, and Maiwashi villages ofHongyuang County in Aba state. X-ray technology was us.ed to diagnose SF, and the daily fluoride intake of each person from brick-tea infusions was determined by a retrospective cohort study. Results: Among the 207 residents examined, the X-ray standardized prevalence rate of SF was 49.76%, which increased with age and poor health, especially among persons over age forty. Both the amount of drinking brick-tea infusions and the amount of fluoride intake from them increased with age and were higher in the SF group than that in the unaffected group. The average daily fluoride intake was 4.49±1.51 mg/person/day) in the SF group and 1.86±1.46 mg/person/day in the unaffected group. The average daily fluoride intake of subjects with different stages or grades of SF was 3.36±1.35 mg (stage I), 4.96±1.44 mg (stage II), and 6.42± 1.33 mg (stage III), respectively. There was a significant (p<0.05) positive linear correlation between the logarithm of daily fluoride intake from brick-tea and the prevalence of SF in each age group. The 95% normal upper-limit for daily fluoride intake from brick-tea was 3.37 mg/person/day, but the 90% unilateral upper-limit was 2.94 mg/person/day, which reflected the SF status more truly and avoided missing and misjudging diagnosis. Conclusion: (1) Along with increasing age, the amount of drinking brick-tea infusions and the amount of fluoride intake also increased; the prevalence of SF was greater; and the degree of fluorosis was more severe-all showing a hlgh regularity and correlation among them. (2) The normal upper limit of fluoride intake from brick-tea among person without SF was lower than the total fluoride intake allowed in the health criteria for drinking water in endemic fluorosis areas.