Neighbourhood greenness might impact thyroid hormone levels in children, adolescents, and young adults

Abstract

Background: Growing attention has been paid to the health benefits of neighbourhood greenness in urban cities, whereas the potential impacts on thyroid hormone levels remain unclear, particularly among children, adolescents, and young adults. Methods: This longitudinal cohort study included 57,198 participants aged 6–25 years from an open cohort in Taiwan, observed from 2000 to 2017. Individual thyroid stimulating-hormone (TSH) and free thyroxine (FT4) levels were measured using immunoassay analysers. The annual average of Normalized Difference Vegetation Index (NDVI) was derived for each participant's address. Linear mixed models were used to investigate the associations between neighbourhood greenness and TSH and FT4, with analyses conducted separately for males and females. The modifying effects and potential mediators were also evaluated. Results: 49690 participants with 71715 observations were included in this study. Among them, 42.7 % of participants were females. Negative association was found between neighbourhood greenness exposure and TSH level for both females and males, while a positive association was found with FT4 levels only among females. Women exposed to the third quartile of NDVI had lower TSH levels (−7.84e⁻² μIU/ml, 95 % CI: −15.01e⁻², −0.67e⁻²) compared with those in the first quartile of NDVI. Decreased TSH levels of 4.56e⁻² μIU/ml (95 % CI: −8.53e⁻², −0.59e⁻²) and 7.24e⁻² μIU/ml (95 % CI: −12.19e⁻², −2.29e⁻²) were found in males exposed to the third and fourth quartile of NDVI, respectively. Regarding FT4 levels, women exposed to the second quartile of NDVI had increased FT4 levels (2.01e⁻² ng/dl, 95 % CI: 0.19e⁻², 3.82e⁻²). Each SD increase of NDVI was associated with 0.65e⁻² ng/dl (95 % CI: 0.15e⁻², 1.15e⁻²) increase of FT4. Conclusion: Our study provided evidence on the impacts of neighbourhood greenness on thyroid hormone levels among young populations. These findings may reveal potential biological mechanisms and contribute to urban planning and public health strategies.