Aim: Autism Spectrum Disorder (ASD) etiopathogenesis remains unclear, and it is a progressively prevalent condition. It has been demonstrated that vitamin D plays an important role not only in bone metabolism but also in brain maturation. Vitamin D and its metabolizing enzymes are expressed in various cerebral structures, and their deficiency has been observed to be associated with the development of psychiatric disorders. This study aims to investigate the levels of Vitamin D, which is considered to play a significant role in the etiopathogenesis of ASD.

Material and Method: Our study was conducted with a total of two groups, comprising 43 children diagnosed with Autism Spectrum Disorder (ASD) according to the DSM-5 diagnostic and classification system, aged between 2-8 years, who presented to the Child and Adolescent Mental Health and Diseases Outpatient Clinic of Çukurova University Faculty of Medicine. This group was compared with a control group consisting of 43 healthy individuals matched for age and gender. The levels of 25-hydroxy vitamin D (25(OH)D) were measured in both the patient and control groups.

Results: The case group consisted of 7 females and 36 males, while the control group comprised 12 females and 31 males. The mean age of the case group was 50.44±22.72 months, whereas the mean age of the control group was 60.09±27.60 months. Vitamin D levels were calculated as an average of 23.64 ± 12.87 ng/mL in the case group and 18.23 ± 8.61 ng/mL in the control group (p=0.039). In the case group aged between 24-48 months, the average Vitamin D level was 26.12±13.30 ng/mL, compared to 16.88±7.49 ng/mL in the control group (p=0.006). For the case group aged between 49-72 months, the average Vitamin D level was 22.54±11.98 ng/mL, and in the control group, it was 18.63±11.35 ng/mL (p=0.423). In the case group aged 73 months and above, the average Vitamin D level was 15.52±11.66 ng/mL, and in the control group, it was 20.01±7.59 ng/mL (p=0.368). For females, Vitamin D levels in the case group were calculated as an average of 27.91±16.22 ng/mL, compared to 15.07±4.86 ng/mL in the control group (p=0.041). For males, Vitamin D levels in the case group were calculated as an average of 22.88±12.33 ng/mL, and in the control group, it was 19.13±9.28 ng/mL (p=0.175).

Conclusion: In our study, Vitamin D levels were found to be significantly higher in the case group. To understand the reason for this seemingly contradictory situation, a detailed analysis was conducted by dividing the participants into different age groups. Particularly, a significant difference was observed between the two groups during the 24-48 months period, which corresponds to the early stages of diagnosis. It is speculated that this situation may be attributed to the usage of certain vitamins by families based on different recommendations, despite these vitamins not being part of the standard treatment protocol for Autism Spectrum Disorder.