Association between subclinical hypothyroidism and vitamin D deficiency: Insights from a case-control study

Subclinical hypothyroidism (SCH) is biochemically characterized by elevated thyrotropin (thyroid-stimulating hormone [TSH]) levels, while free thyroxine (FT4) levels remain normal. Given the high prevalence of vitamin D deficiency in Iran, investigating the association between vitamin D levels and SCH may improve treatment. A case-control study was conducted at the endocrinology clinic of Imam Khomeini Hospital, affiliated with Ahvaz Jundishapur University of Medical Sciences. A total of 106 subjects who met the inclusion criteria were selected and divided into 2 groups: 53 subjects with SCH and 53 healthy controls (HC). Serum levels of vitamin D, TSH, and FT4 were obtained from medical records. Other variables including age, weight, and height were also recorded. Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) version 26. The mean age of the SCH and HC groups was 35.98 ± 12.9 years and 34.34 ± 13.49 years, respectively. In the SCH group, the mean serum vitamin D level was 23.99 ± 9.26 ng/mL, compared to 26.73 ± 9.42 in the HC group, with no statistically significant difference (P = .10). In both groups, no significant correlation was found between vitamin D levels and variables, such as sex, age, and body mass index. However, the TSH and FT4 levels in the SCH group were significantly higher than those in the control group. No significant difference in vitamin D deficiency was observed between SCH patients and HC.