Spatial and temporal distribution of rotating shift work and thyroid carcinoma incidence in European countries
Table 1 showed demographic characteristics; in the four waves of EWCS, the incidence of TC in women was significantly higher than in men. Spatially, as is shown in Fig. 2(a), the prevalence of total RSW declined from 9.56% in 2005 to 9.54% in 2010, and then it rose to 10.17% by 2015. Over the same period, total TC incidence declined from 5.4(per 100,000) in 2010 to 5.2(per 100,000) in 2015, and then it rose to 5.31(per 100,000) in 2020. Also, the prevalence of female RSW declined from 9.89% in 2005 to 7.53% in 2010, then rose to 11.91% by 2015. Over the same period, female TC incidence declined from 7.05(per 100,000) in 2010 to 6.77(per 100,000) in 2015, and then it rose to 5.87(per 100,000) in 2020. However, there is no obvious trend among male workers. Meanwhile, as is shown in Fig. 2(b), among all workers, RSW ranges from 2.61% (Cyprus, 2010) to 23.90% (Montenegro, 2010), and TC5 incidence ranges from 2.78 (per 100,000 people) (Bulgaria, 2001) to 11.10 (per 100,000 people) (Italy, 2000). Among female workers, RSW ranged from 1.55% (Turkey, 2010) to 26.58% (Montenegro, 2010), and TC5 incidence ranged from 3.56 (per 100,000) (Bulgaria, 2001) to 14.66 (per 100,000) (Italy, 2000). Among male workers, RSW ranged from 2.00% (Denmark, 2010) to 22.01% (Montenegro, 2010) and TC5 incidence ranged from 1.61 (per 100,000) (FYROM, 2010) to 7.92 (per 100,000) (Italy, 2015).
Covariates and thyroid carcinoma incidence
As listed in Table 2, Spearman rank correlation analysis showed that TC incidence was significantly correlated with GDP per capita(r=0.27,p=0.002), age(r=0.2,p=0.024)and occupational radiation exposure (r=-0.21,p=0.023), but not significantly with education attainment rate(r=0.02,p=0.862) and obesity rate(r=0.04,p=0.698).And also, the T-test showed a significant difference between volcanic and non-volcanic areas (P=0.004). However, when the regional variable was controlled, Spearman rank correlation analysis showed that education attainment rate was obvious correlated with TC incidence in both volcanic (r=-0.35, P=0.031) and non-volcanic (r=0.25, P=0.032) regions. And obesity is a well-known risk factor for TC. Therefore, the education attainment rate and obesity rate still need to be included in the analysis.
The relationship between rotating shift work and thyroid carcinoma incidence
As is shown in Table 3, we used a mixed linear model to control the autocorrelation of TC5 incidence caused by repeated measurements of the same countries. Although there was no statistically significant association between RSW and TC5 incidence(β=0.00,95%CI:-0.03,0.02;P=0.928), when the confounding factors included the country-specific, GDP per capita, volcanic region, the median age of rotating shift workers, education attainment rate, obesity rate, and occupational radiation exposure rate were adjusted, there was a significant association between RSW and TC5 incidence. Each percent increase in RSW prevalence was linked to 0.03/100000 people higher TC5 incidence (95%CI:0.01,0.06;P= 0.029) (Table 3). For every quartile increase in total RSW, the TC5 incidence increased by 0.18(95%CI:0.05,0.30; P=0.009) (per 100000 people) (Fig. 3(a)).
Furthermore, the sex-specific relationship between RSW and TC incidence was analyzed. As is shown in Table 3, before adjusting for confounding factors, the association between female RSW and female TC5 incidence was not statistically significant(β=0.02,95%CI:-0.01,0.05; P=0.210), while male RSW was correlated with male TC5 incidence(β=-0.02,95%CI:-0.05,0.00; P=0.030). However, after controlling the confounding factors, each percent increase in female RSW prevalence was associated with 0.04/100000 people higher TC5 incidence(95%CI:0.01,0.08; P=0.018)(Table 3). For every quartile increase in female RSW, the TC5 incidence increased by 0.29(95%CI:0.07,0.31, P=0.001) (per 100000 people) (Fig. 3(b)). On the other hand, in men, RSW was not associated with the TC5 incidence (β=0.01,95%CI:-0.03,0.04, P=0.749)after the confounding factors were controlled (Table 3).