Energy, protein, and iodine intakes
A total of 4646 qualified subjects were investigated and included in the analysis except those who were loss to follow-up, did not have complete recordings or had previous thyroid diseases. The median of energy, protein and iodine intake was 1985.6 kcal, 80.1g and 119.1μg, respectively. Among the subjects, 62.3% exceeded protein RNI and 19.0% exceeded iodine RNI (Table 1).
Characteristics and thyroid antibodies stratified by animal protein
The positive rate of TPO-Ab, TG-Ab, TR-Ab and TPO-Ab / TG-Ab b / TR-Ab was 10.40%, 9.43%, 8.47% and 20.56% in all subjects, respectively.
According to the animal protein intake, the subjects were divided into three tertiles: bottom third intake (< 30.9 g/d), middle third intake (30.9–50.3 g/d), and top third intake (> 50.3 g/d). In the pooled sample, there were significant differences in the constituent ratio of educational level and family income last year among the three animal protein intake groups (P < 0.05). Just looking at the data, the proportions of better educational background and higher family income last year were higher in the middle third intake group. The median UIC in pregnant women was 139.3 μg/L. There were no significant differences in age, median UIC, occupational status, and alcohol consumption among the three animal protein intake groups. The results of the different gestational stages are shown in Table 2.
The TR-Ab positive rate was significantly different in the pooled sample (P < 0.05). Pairwise comparisons were performed among the three groups. The findings showed that the TR-Ab positive rate was higher in the bottom third intake group than in the other two groups (P < 0.05). TPO-Ab positive rate was higher in the middle pregnancy in top third intake group than in the other groups (P<0.05).
Energy, protein, and iodine intakes and UIC in thyroid antibody positive and negative groups
UIC and intakes of energy, total protein, animal protein (including milk protein), and iodine were compared between thyroid antibody positive and negative groups (table 3). The results showed that there was no significant difference in energy intake between both groups. In the pooled sample, the difference in UIC between TPO-Ab positive and negative groups was statistically significant (P < 0.05), and there was a statistically significant difference in total protein intake, animal protein intake, and UIC between TR-Ab positive and negative groups and in total protein intake and UIC between TPO-Ab/TG-Ab/TR-Ab positive and negative groups (P < 0.05).
Factors associated with positive thyroid antibodies
Multivariable logistic regression analyses were conducted using general characteristics, animal protein intake (including milk protein), UIC, and other related factors as independent variables and thyroid antibodies as dependent variables (Table 4).
Compared to the bottom third animal protein intake, the middle third and the top third animal protein intake served as protective factors for positive TR-Ab (coefficient = 0.559, 95% CI = 0.415–0.752, P = <0.001; coefficient = 0.0.406, 95% CI = 0.266–0.621, P = <0.001) and positive TPO-Ab/TR-Ab/TG-Ab (coefficient = 0.817, 95% CI = 0.687–0.971, P = 0.022; coefficient = 0.805, 95% CI= 0.672–0.964, P = 0.018), respectively. There was no significant association between animal protein intake and positive TPO-Ab or positive TG-Ab.
Compared to the low educational level, the senior high school and college level and Bachelor degree and above level served as protective factors for positive TR-Ab and TPO-Ab/TR-Ab/TG-Ab. Mental work compared with physical work served as risk factors for positive TPO-Ab, TG-Ab and TPO-Ab/TR-Ab/TG-Ab. The insufficient iodine group compared with adequate iodine group served as risk factors for positive TPO-Ab, TR-Ab and TPO-Ab/TR-Ab/TG-Ab. > 30% energy from fat compared with ≤ 30% served as risk factors for positive TPO-Ab and TR-Ab. The above differences were statistically significant, P < 0.05.