During a median follow-up of 3.10 years (maximum 7.56 years; minimum 2.00 years), 2669 cases of T2D were identified (788 women and 1881 men) among a total of 116,816 participants (53,977 females, 62,854 males). The age-standardized incidence of diabetes was 12.87 per 1000 person-years (women: 11.04; men: 14.69). Men had higher levels of basic clinical data (height, body weight, body mass index, and systolic and diastolic blood pressure), lifestyle data (smoking and alcohol consumption) and biochemical tests (FPG, LDL, total cholesterol and triglyceride) (Table S1). The FPG changes in women was 0.19 ± 0.60 mmol/L lower than that in men (0.25 ± 0.72 mmol/L).
Almost all the fitting curves of diabetes probability of FPG changes were nonlinear and showed a sectional activity that conformed to the hook-like pattern: an initial decrease, then transient sharp elevation, followed by a slow increase. Hence, FPG changes were categorized into three stages based on the curves by two turning points (overall: -0.04 and 1.25; women: -0.05 and 1.16; men: -0.24 and 1.32, mmol/L) (Fig. 1). Importantly, the hook-like pattern was maintained, which was reconstructed via different levels of age, sex, HDL, TG, TC, SBP, DBP and history of diabetes (Fig. S1). Only the curves in participants with LDL ≥ 4.1 mmol/L and/or BMI < 18.5 kg/m2 had two stages (Fig. S1). We also found differences in the baseline characteristics of the participants (Table 1). There were similar baseline characteristics in participants with stage-1 and stage-2 FPG changes. However, participants with stage-3 had significantly different basic clinical data (body weight, body mass index, and systolic and diastolic blood pressure) and biochemical tests (LDL, total cholesterol, triglyceride, ALT and AST) in both women and men. Interestingly, from stage-1 to stage-3, the baseline FPG concentration continued to drop and all participants with diabetes in stage-1 were all diagnosed by self-reported (in Table S2). We also found participants with FPG baseline more than 5.6 mmol/L had a higher proportion of diabetics than those with a baseline FPG of less than 5.6 mmol/L both in women and men (in Table S2).
Table 1
Baseline characteristic of participants according to sex and stages of FPG changes (mmol/L)
| Women | Men |
Stage-1 < -0.24 | Stage-2 -0.24–1.15 | Stage-3 ≥ 1.16 | P-value | Stage-1 < -0.05 | Stage-2 -0.05–1.31 | Stage-3 ≥ 1.32 | P-value |
N | 12076 | 39132 | 2762 | | 21238 | 38353 | 3255 | |
Age (years) | 43.40 ± 12.64 | 43.40 ± 12.39 | 48.96 ± 14.26 | < 0.001 | 44.10 ± 13.25 | 44.26 ± 13.06 | 48.38 ± 13.64 | < 0.001 |
Height (cm) | 160.08 ± 5.64 | 160.11 ± 5.63 | 159.20 ± 5.98 | < 0.001 | 171.61 ± 6.26 | 171.68 ± 6.21 | 171.49 ± 6.41 | 0.162 |
Weight (kg) | 56.97 ± 8.24 | 56.73 ± 8.09 | 58.50 ± 9.10 | < 0.001 | 71.67 ± 10.64 | 71.57 ± 10.49 | 74.41 ± 11.54 | < 0.001 |
BMI (kg/m2) | 22.24 ± 3.08 | 22.13 ± 3.02 | 23.10 ± 3.51 | < 0.001 | 24.31 ± 3.17 | 24.26 ± 3.14 | 25.27 ± 3.45 | < 0.001 |
SBP (mmHg) | 115.32 ± 16.37 | 114.80 ± 16.53 | 121.72 ± 20.26 | < 0.001 | 123.03 ± 15.60 | 122.70 ± 15.61 | 126.15 ± 17.71 | < 0.001 |
DBP (mmHg) | 71.48 ± 10.32 | 71.30 ± 10.42 | 74.90 ± 11.62 | < 0.001 | 76.69 ± 10.61 | 76.83 ± 10.71 | 79.93 ± 11.70 | < 0.001 |
FPG (mmol/L) | 5.29 ± 0.47 | 4.79 ± 0.51 | 4.42 ± 0.80 | < 0.001 | 5.34 ± 0.50 | 4.84 ± 0.57 | 4.62 ± 1.00 | < 0.001 |
TC (mmol/L) | 4.81 ± 0.93 | 4.75 ± 0.91 | 4.89 ± 0.92 | < 0.001 | 4.84 ± 0.90 | 4.78 ± 0.87 | 4.86 ± 0.88 | < 0.001 |
TG (mmol/L) | 1.12 ± 0.82 | 1.07 ± 0.72 | 1.28 ± 0.90 | < 0.001 | 1.65 ± 1.24 | 1.59 ± 1.13 | 1.84 ± 1.31 | < 0.001 |
HDL-C (mmol/L) | 1.48 ± 0.31 | 1.47 ± 0.31 | 1.47 ± 0.31 | 0.011 | 1.29 ± 0.27 | 1.29 ± 0.28 | 1.24 ± 0.27 | < 0.001 |
LDL-C (mmol/L) | 2.78 ± 0.70 | 2.73 ± 0.69 | 2.80 ± 0.67 | < 0.001 | 2.83 ± 0.69 | 2.77 ± 0.66 | 2.80 ± 0.65 | < 0.001 |
ALT (IU/L) | 17.18 ± 13.82 | 17.17 ± 14.97 | 21.00 ± 42.88 | < 0.001 | 28.87 ± 21.55 | 29.27 ± 24.07 | 33.83 ± 30.97 | < 0.001 |
AST (IU/L) | 21.84 ± 10.48 | 21.69 ± 9.01 | 24.44 ± 27.94 | < 0.001 | 25.61 ± 10.60 | 25.76 ± 13.81 | 28.39 ± 19.92 | < 0.001 |
BUN (mmol/L) | 4.44 ± 1.15 | 4.37 ± 1.12 | 4.44 ± 1.18 | < 0.001 | 4.99 ± 1.18 | 4.91 ± 1.14 | 4.89 ± 1.16 | < 0.001 |
CCR (µmol/L) | 57.82 ± 9.76 | 58.42 ± 10.51 | 59.10 ± 11.66 | < 0.001 | 80.43 ± 12.01 | 80.71 ± 11.97 | 79.47 ± 11.99 | < 0.001 |
FPG of final visit (mmol/L) | 4.76 ± 0.43 | 5.10 ± 0.48 | 6.03 ± 1.22 | < 0.001 | 4.93 ± 0.48 | 5.31 ± 0.55 | 6.66 ± 1.82 | < 0.001 |
Family history of diabetes, N (%) | 355 (2.94%) | 1162 (2.97%) | 92 (3.33%) | 0.533 | 321 (1.51%) | 627 (1.63%) | 82 (2.52%) | < 0.001 |
Continuous variables are presented as the mean ± standard deviation (normal distribution); categorical variables are presented d as number (%). FPG changes was defined as the difference between the baseline and final visit FPG (FPG2) (mmol/L). ALT, alanine aminotransferase; AST, aspartate transaminase; BMI, body mass index; BUN, blood urea nitrogen; CCR, endogenous creatinine clearance rate; DBP, diastolic blood pressure; FPG, fasting plasma glucose; HDL-C, high-density lipoprotein cholesterol; MBP, mean systolic blood pressure; LDL-C, low-density lipoprotein cholesterol; SBP, systolic blood pressure; TC, total cholesterol; TG, triglyceride. $ N (%) refers to the number and proportion of the identical sex group. # Diagnosis of incident diabetes was defined as fasting plasma glucose of ≥ 7.00 mmol/L and/or self-reported diabetes during the follow-up period. All trend for baseline characteristic of participants among age and groups, P < 0.001. In women: stage-1: < -0.24 mmol/L; stage-2: -0.24–1.15 mmol/L; stage-3: ≥ 1.16 mmol/L. In men: stage-1: < -0.05 mmol/L; stage-2: -0.05–1.31 mmol/L; stage-3: ≥ 1.32 mmol/L. |
Importantly, the incidence of T2D varied with sex and the stages of FPG changes (stage-1: women 1.46, men 2.09, overall, 1.86; stage-2: women 2.14, men 5.59, overall, 3.86; stage-3: women 48.20, men 92.07, overall, 72.45, per 1000 person-years). HR per SD of FPG changes on incident diabetes was also affected by sex and stages of FPG changes. From stage-1 to stage-3, the HRs per SD of FPG changes in women were 0.10 (0.06, 0.18), 4.28 (3.07, 5.98) and 1.56 (1.50, 1.63), respectively; the HRs per SD in men were 0.20 (0.13, 0.30), 8.32 (6.73, 10.29) and 1.27 (1.24, 1.30), respectively; and the overall HRs per SD were 0.16 (0.12, 0.23), 0.20 (0.15, 0.28) and 0.22 (0.16, 0.31), respectively. Compared with stage-1, in women, the HR in stage-3 was significantly higher [22.08 (16.47, 29.59)], while the increase in stage-2 was not significant [1.12 (0.82, 1.51), P > 0.05]; in men, the HR in stage-2 slightly increased to 1.81 (1.54, 2.12), and that in stage-3 rose to 30.09 (25.02, 36.19).
Kaplan-Meier survival curves for cumulative diabetes-free probability based on sex and the stages of FPG changes are presented in Fig. 2. The cumulative diabetes-free probability was approximately 90% in stage-1 and stage-2 and in both stages at the end of the follow-up period. However, in stage-3, the cumulative diabetes-free probability decreased sharply with the increase in FPG changes, especially in the upper tertile of stage-3, which was close to zero at the end of follow-up (Fig. S2).
We also compared the differences in the correlation between FPG changes and other metabolic markers with the incidence of diabetes by ROC curve analyses (Fig. S3). The area under the curve (AUC) by bootstrap varied with sex: FPG changes 0.864 [0.854, 0.873] (women 0.846; men 0.869), TyG index 0.766 [0.757, 0.774] (women 0.800; men 0.723) and TG/HDL ratio 0.699 [0.690, 0.709] (women 0.740; men 0.646). The predictive model based on FPG changes had better sensitivity (76.83%) and specificity (84.19%) than the model based on the TG/HDL ratio (67.78% and 62.35%, respectively) and TyG index (77.77% and 63.10%, respectively). FPG changes had a higher association with the onset of T2D in both men and women.