Background: Radiation exposure is a well-known risk factor for thyroid cancer. However, the specific effects of diagnostic radiation exposure on thyroid cancer risk are controversial. The purpose of this study was to perform a systematic review and meta-analysis to assess the effects of diagnostic radiation exposure on thyroid cancer risk. Methods: The PubMed and EMBASE databases were searched to identify eligible studies. Summary odds ratio (OR) estimates and 95% confidence intervals (CIs) were used to compute the risk of thyroid cancer using fixed- and random-effects models. Subgroup and sensitivity analyses were performed to evaluate the potential heterogeneity. Results: Nine studies from twelve publications were included in the meta-analysis. Overall exposure to diagnostic radiation exposure was associated with a significantly increased thyroid cancer risk (summary OR=1.52, 95% CI=1.13–2.04). The subgroup and sensitivity analyses revealed similar results. By type of exposure, exposure to CT scans (OR=1.46, 95% CI=1.27–1.68) or dental x-rays (OR=1.69, 95% CI=1.17–2.44) were associated with an increased thyroid cancer risk. Head and neck (OR=1.31, 95% CI=1.02–1.69) and chest (OR=1.71, 95% CI=1.09–2.69) exposure to diagnostic radiation was associated with an increased thyroid cancer risk. Conclusions: The results of this meta-analysis indicates that diagnostic radiation exposure is associated with an increased thyroid cancer risk. Therefore, to the extent that it will not compromise the information being sought, radiation exposure to the thyroid should be minimized during diagnostic examinations.

Previous epidemiological studies have reported persistent organic pollutants (POPs) and some nonpersistent pesticides and the risk of thyroid cancer. The aim of this study was to assess the association between exposure to POPs, pesticides, and thyroid cancer by carrying out a meta-analysis. Literature searches were performed using PubMed, Embase, and reference lists of relevant articles. Summary risk estimates for thyroid cancer were calculated using fixed-effects and random-effects models. In addition, several subgroup and sensitivity analyses were carried out. Fifteen studies were reviewed, and eight studies were included in the meta-analysis. Pesticide exposure showed positive, statistically significant associations with thyroid cancer [odds ratio (OR)=1.48, 95% confidence interval (CI)=1.15–1.91, I ²=48%, P _{heterogenetiy}=0.05]. After subgroup analysis, herbicide exposure (OR=3.00, 95% CI=1.38–6.54) and agricultural exposure to pesticides (OR=1.86, 95% CI=1.04–3.32) was associated with an increased risk of thyroid cancer. A sensitivity analysis showed that the results were robust. Exposure to pesticides was associated with an increased risk of thyroid cancer in this meta-analysis. Future studies should investigate exposure to POPs or pesticides with controls for potential confounders using biological samples.

Kim JH, et al. Diabetes Metab J. 2013 Dec;37(6):423-428. http://dx.doi.org/10.4093/dmj.2013.37.6.423

Background: A possible prothrombotic effect of elevated thyrotropin (TSH) has been suggested. The mean platelet volume (MPV), which is used to measure the platelet size, can reflect platelet activity. Although limited and inconsistent data regarding the effects of thyroid function on the MPV are available from small-scale case-control studies, no study has been based on a general population, particularly in euthyroid states. The objective of the present study was to determine whether there is an association between the MPV and serum TSH concentrations in an apparently healthy Korean population without overt thyroid disease, but including subjects with unsuspected subclinical hypothyroidism (SCH). Methods: We retrospectively studied 6893 asymptomatic Korean adults who were 20 years of age or older and who underwent voluntary regular health check-ups at the Health Promotion Center of Chosun University Hospital. The subjects who met the inclusion and exclusion criteria were subdivided into four groups, such as tertile groups for the TSH reference range and an SCH (TSH ≥4 μIU/mL with a normal free T4 concentration) group according to the TSH level. We compared the mean values of the MPVs among the groups. Multivariate logistic regression analyses were used to identify associations between the highest tertile of the MPV and the TSH subgroups. Results: The mean level of the MPV in all study subjects was 8.12±0.75 femtoliters (fL), and the mean value of the MPV was significantly different in each group. The mean MPV in SCH was significantly higher compared with those of the first tertile (T1) and second tertile (T2). Moreover, the mean MPV increased statistical significantly by increasing tertiles of the TSH concentration and was highest in SCH (T1, 8.08±0.81 fL; T2, 8.09±0.62 fL; T3, 8.13±0.77 fL; SCH, 8.21±0.81 fL; p for trend=0.012). After adjusting for risk factors associated with increasing MPVs and platelet counts, SCH was independently associated with the highest tertile of the MPV (all subjects, odds radio (OR) 1.58 [95% confidence interval (CI) 1.19–2.09]; men, OR 1.70 [CI 1.10–2.64]; women, OR 1.55 [CI 1.06–2.26]). Conclusions: The MPV was positively correlated with the TSH level. SCH is an independently associated factor with the highest tertile of MPV in a general Korean population. We propose that the MPV may contribute to the prothrombotic condition that is associated with SCH and perhaps even in putative euthyroid states where the TSH level is the higher part of the normal range.