Effect of temperature changes on the occurrence of congenital hypothyroidism

Abstract

Objectives To investigate an association between seasonal changes in temperature and the prevalence of congenital hypothyroidism (CH) in the Southwest of Iran. Methods A prospective two-year study conducted from March 2007 to March 2009 during the nationwide screening programme for CH in Ahvaz, the biggest city in southwest Iran. Blood samples were taken from almost all newborns by heel-stick and used in a thyroid-stimulating hormone (TSH)-enzyme-linked immunosorbent assay (ELISA). Serum thyroxine (T4) and TSH were measured if the ELISA-TSH was .5 mIU/L (suspicious cases). Infants were considered to have CH with T4 ,6.0 mg/dL and TSH . 10 mIU/L, or with normal T4 values and persistent high TSH values for .2 months (subclinical hypothyroidism). Date of birth and sex were recorded. Detailed temperature data were obtained from the meteorological organization. The relationship between the monthly incidence of CH and the average monthly temperature was investigated.Results From 47,075 (50.92% male) newborns, 1131 were referred (recall rate ¼ 2.4%) and 142 infants (51.4% male) were confirmed to have CH. The seasonal distribution of CH cases was 32.4% in the warm period and 67.6% in the cold period of the year (19%, 13.4%, 32.4% and 35.2% in spring, summer, fall and winter, respectively; P ¼ 0.001). A statistical difference was seen between mid-summer (2.8%, warmest time) and early winter (15.5%, coldest time). The above-mentioned difference was the same for suspicious individuals (P , 0.001). The odds of being affected were increased by 4% for each fall of 18C. Conclusion The prevalence of CH has a significant negative correlation with the temperature in the tropical area of Iran.

Clinical and environmental influences on metabolic biomarkers collected for newborn screening

“…Another explanation for seasonal associations with analyte concentrations include biological influences directed by environmental stimulates such as temperature which has been documented for CH [32-35]. CH is found in approximately 1 out of 4,000 newborns and results in thyroid hormone deficiency at birth.…”

“…Interestingly, we observed similar trends to studies demonstrating that the incidence of suspected and confirmed cases of congenital hypothyroidism is increased in the winter. Studies that have demonstrated an increase in CH in the winter months have been conducted in Japan, Britain, Finland and Iran, indicating this is an effect that is observed globally in geographic areas with varying climates [32-36]. While permanent CH is due to genetic inheritance that is not affected by temperature, it is possible that intrauterine viral infection, seasonal influences on food products and influence of temperature, acting through exposure to seasonally-affected environmental factors, on gene expression patterns or human leukocyte antigen backgrounds contribute to this finding [32,33].…”

High prevalence of congenital hypothyroidism in Isfahan: Do familial components have a role?

“…The results of the nationwide CH screening program have also indicated the high prevalence of CH in Iran. [10]…”

Thyroid scintigraphy in three-year-old children with congenital hypothyroidism in correlation with neonatal TSH

“…Seasonal distributions were found to be as follows: spring: 25.7%, summer: 27.9%, autumn: 20.3%, and winter: 26.1%. The author's previous study (6) in this region had disclosed a different pattern: spring: 19%, summer: 13.4%, autumn: 32.4%, and winter: 35.2%. In an opposite direction, Hashemipour et al [24] reported a higher prevalence of CH in the warm season of the year.…”

“…Congenital hypothyroidism (CH) was reported to be more prevalent in the Asian population [1]. A large number of cases were reported as transient [2,3], possibly caused by maternal and/or environmental factors [4][5][6]. In these situations, the clinician must be careful to avoid unnecessary treatment while not losing any Majid Aminzadeh, Associate Professor of Paediatric Endocrinology and Metabolism, Paediatric Department, Abuzar Children's Hospital, Pasdaran Blvd., Ahvaz, Iran, tel/fax: (+98) 61 344 337 15; e-mail: aminzadeh_m@ajums.ac.ir, aminzadehmajid@yahoo.com; ORCID: 0000-0002-0931-7432  Thyroid scintigraphy in congenital hypothyroidism Majid Aminzadeh (AJUMS).…”