A novel U‐shaped relationship between BMI and risk of generalized aggressive periodontitis in Chinese: A cross‐sectional study

Abstract Background Association between BMI and periodontitis were controversial. A study indicated that not only overweight or obesity but also underweight was correlated with generalized aggressive periodontitis (GAgP). However, the exact relationship between BMI and GAgP and the optimal BMI value for the lowest risk of GAgP remain unknown. Objective To explore the exact relationship between BMI and GAgP risk, periodontal status and WBC (white blood cell) count and find the optimal BMI value associated with the lowest risk, periodontal status and lowest WBC of GAgP in Chinese. Methods 300 GAgP patients and 133 healthy controls were recruited. Height and weight of participants were accurately measured to calculate BMI value. Clinical periodontal parameters, including probing depth (PD), attachment loss (AL), and bleeding index (BI) were recorded. WBC was obtained from routine blood examination. Smooth curve fitting and segmented regression model were used to analyze the threshold effect between BMI and variables. The shape of the curve was used to describe the relationships between BMI and GAgP. Results U‐shaped relationships between BMI and risk of GAgP, AL, and WBC count in GAgP patients were observed. The optimal value of BMI for the lowest risk of GAgP and lowest WBC count was 22 kg/m 2 . The risk of GAgP increased by 39% in patients per unit increase of BMI when BMI ranged from 22 to 28 kg/m 2 (adjusted OR = 1.39, 95% CI: 1.17, 1.67) and increased by 18% per unit decrease of BMI when BMI ranged from 22 to 18 kg/m 2 (adjusted OR = 0.82, 95% CI: 0.69, 0.97). The count of WBC increased by 1.12 × 10 9 /L in patients per unit increase of BMI when BMI ranged from 22 to 28 kg/m 2 (adjusted β = 0.12, 95% CI: 0.01, 0.23) and increased by 0.2 × 10 9 /L per unit decrease of BMI when BMI ranged from 22 to18 kg/m 2 (adjusted β = −0.2, 95% CI: −0.35, −0.04). Conclusion U‐shaped relationships exist between BMI and risk of GAgP, AL, and WBC count in patients with GAgP among Chinese aged below 36 years old with their BMI range from 18 to 28 kg/m 2 ; the optimal BMI value for lowest odds ratio and lowest WBC count of GAgP was 22 kg/m 2 .