Catherine L. McHugh, MA, BCBA, LBA and Thomas Zane, PhD, BCBA-D
Department of Applied Behavioral Science, University of Kansas

A quick Internet search on autism spectrum disorder (ASD) will easily yield countless results that include articles written by individuals with autism, parents, and professionals alike. The difficult part is parsing through this material to find the information being sought. Articles on the medical interventions for the treatment of ASD is one such category of interest. These studies are often medical in nature and consist of highly technical language with results that are not easily interpreted. There are some studies in the literature that suggest vitamin D deficiencies before birth may contribute to a diagnosis of ASD later in life (e.g., Cannell, 2017; Khamoushi et al., 2019; Kocovska et al., 2012; Mazahery et al., 2016). In addition, there have been a small number of studies suggesting that there is a possible link between vitamin D levels and ASD, and that one may be able to treat the core symptoms of ASD in childhood by giving vitamin D supplements. The logic seems fairly simple and the administration of an over-the-counter vitamin may appear to be low-risk and high reward but do the risks outweigh the benefits? To find out, one must turn to the research behind this purported treatment to determine, what is the science behind this?

Current research on treatment

The current body of research on vitamin D supplementation as a treatment for the core symptoms of ASD is very small and relatively new. A search of Google Scholar articles with the keywords “autism spectrum disorder”, “vitamin D”, and “treatment” resulted in 16,600 results. However, upon further review, the majority of these studies evaluated the role of vitamin D deficiencies in the emergence of ASD symptoms. Two studies and one meta-analysis were found using this vitamin for actual treatment of ASD symptoms in children. First, Saad and colleagues (2018) conducted a randomized controlled trial of vitamin D supplementation in children with ASD and reported that the group that received the vitamin D showed significant effects on the manifestation of the core symptoms of ASD. However, as we will discuss later, this article was formally retracted (Cicero, 2020). Javadfar and colleagues (2020) used a group design to evaluate vitamin D supplementation. According to the authors, results suggested that, “vitamin D supplementation could ameliorate autism spectrum disorder symptoms” (p. 5). Finally, Song et al. (2020) conducted a meta-analysis on current research in this area and reported that vitamin D supplementation may be beneficial for improving symptoms of ASD.

Issues with the current research

At first glance, this research seems promising. However, there are several issues with the current literature that lower the confidence that vitamin D had any real positive impact on the children with whom it was used. First, researchers in the field of autism and medicine have criticized the Saad et al. (2018) article for methodological flaws. For example, Beale (2018) asserted that the Saad et al. (2018) study showed insufficient evidence for the results claimed. Beale (2018) noted that the sample size was too small for the type of analysis conducted, and there was questionable consistency with the evaluation. Beale (2018) concluded that the validity of the results could not be verified. The journal editors (who published the Saad and colleagues paper) themselves noted several discrepancies, eventually concluding that they no longer had confidence in the quality of this research and the findings, and decided to retract that paper. They also wrote a response to explain what they found and why they retracted it from the journal publication (Sonuga-Barke & John-Wiley & Sons, 2019).

Further, the results from Javadfar et al. (2020) are not without potential limitations. The authors stated that the test group showed an increase in vitamin D levels after treatment when compared to the control group and they reported that the test scores used were improved in the treatment group when compared to the placebo group. The authors noted two limitations including a small sample size and a short period of supplementation. It is unclear how much vitamin D was consumed and over what period of time may be required to see a noticeable change, if at all. Further, there was no detail on possible other confounding variables such as other treatments or therapies that the participants might have been receiving simultaneously. Therefore, it is unknown if it was the Vitamin D or other ongoing treatments that improved the participants scores.

Finally, the study by Song et al. (2020) appeared to have found promising results, but potential limitations also exist here. The authors established criteria for including articles in their review: (1) children with ASD, (2) under the age of 18, (3) specific vitamin D levels were investigated, (4) significant differences existed in vitamin D levels after interventions, and (5) the use of randomized control trials. However, upon further review, the authors did not directly address the issue at hand, namely vitamin D treating ASD symptoms. The only criteria that might have addressed this vitamin was a reference to, “… studies in which vitamin D supplementation was the intervention” but likely should include “for symptoms of ASD” (p. 204). However, the authors did not measure any observable behavior or autism symptoms pre- or post-treatment. The data they presented were solely focused on vitamin D levels and scores on standardized rating scales, and did not examine any specific characteristics of autism and whether there were changes after administering vitamin D. The authors were merely making inferences based on possible correlations between vitamin D levels and a diagnosis of autism. In summary, this does not address the aim of their study which was to suggest that vitamin D may reduce characteristics of autism – but the data do not reflect that.

Additionally, the authors stated that the first search yielded 452 articles but upon further evaluation only 203 cases were included. However, it remains unclear how they defined cases. That is, they could be including multiple cases (participants) from the same article. Further, the results of the meta-analysis could use more clarity. One thing that is clear, but obviously expected, is that groups that received vitamin D supplementation presented with higher levels of vitamin D after treatment when compared to controls who did not receive vitamin D. However, the section regarding ASD symptoms does not provide any reference to what studies they were taken from or what the interventions included – only that assessment scores improved.

Overall, the Song et al. (2020) article should be interpreted with caution. The authors definitively state that according to these studies, vitamin D improved ASD symptoms with no real data available to help support these claims. Finally, the reference section of this study contains mostly articles around diagnosis, etiology, and prevalence of ASD along with studies about the role of vitamin D in the presentation of ASD symptoms. There were no studies that suggested the evaluation of vitamin D as a treatment for ASD.

Taken together, although the current body of literature on vitamin D supplementation appears to report promising results, only one of the two (with the third being the meta-analysis) may be considered as valid as the other was retracted.

Future research

Based on the paucity and ambiguity of the literature available, it appears that vitamin D supplementation has no impact on ASD symptoms. To put it another way, there is little quality evidence that vitamin D can be responsible for positive changes in autism symptomology. Supplementation with vitamin D may impact overall health (Cleveland Clinic, 2019) and potential vitamin D deficiencies (Cleveland Clinic, 2019). However, it should not be used as an intervention to treat the symptoms of ASD. It is not evidenced-based at this point. Future research could explore early detection of ASD and the possible link between vitamin D levels in infants and the emergence of ASD.

Final thoughts

Parents and caregivers face an array of potential treatment options. In order to preserve time, money, and energy, evidence-based strategies need to be at the forefront of consideration and selection. Although the American Academy of Pediatrics does recommend vitamin D supplementation in certain healthy infants, children, and adolescents to prevent rickets and vitamin D deficiency (Wagner & Greer, 2008), the administration of vitamin D as a therapy for ASD should be considered a fad treatment.

The research base is small; the results are ambiguous at best and show ineffectiveness at least. There are tried and true methods that have been investigated and found to have quality research evidence to support them. Parents and caregivers should pay attention to them and refrain from using vitamin D therapy until the time of quality evidence supports positive effects.

References

Beale, D. J. (2018). Letter to the Editor: Unreported statistics lead to unverifiable results in study of vitamin D supplementation in children with autism spectrum disorder – Comment regarding Saad, K., et al. (2016). Journal of Child Psychology and Psychiatry, and Allied Disciplines, 59(1), e1. https://doi.org/10.1111/jcpp.12776

Cannell, J. (2017). Vitamin D and autism, what’s new? Reviews in Endocrine and Metabolic Disorders, 18, 183-193. http://doi:10.1007/s11154-017-9409-0

Cicero, F. (2020). Perspectives: An unexpected journey into retraction. Science in Autism Treatment, 17(9).

Cleveland Clinic. (2019). Vitamin D deficiency. https://my.clevelandclinic.org/health/articles/15050-vitamin-d–vitamin-d-deficiency

Javadfar, Z., Abdollahazad, H., Moludi, J., Rezaeian, S., Amirian, H., Foroughi, A. A., Nachvak, S. M., Goharmehr, N., & Mostafai, R. (2020). Effects of vitamin D supplementation on core symptoms, serum serotonin, and interleukin-6 in children with autism spectrum disorders: a randomized clinical trial. Nutrition, 79, 1-6. https://doi.org/10.1016/j.nut.2020.110986

Khamoushi, A., Aalipanah, E., Sohrabi, Z., & Akbarzadeh, M. (2019). Vitamin D and autism spectrum disorder: A review. International Journal of Nutrition Science, 4(1), 9-13. https://dx.doi.org/10.30476/ijns.2019.81436.1004

Kocovska, E., Fernell, E., Billstedt, E., Minnis, H., Gillberg, C. (2012). Vitamin D and autism: Clinical review. Research in Developmental Disabilities, 33, 1541-1550. https://doi.org/10.1016/j.ridd.2012.02.015

Mazahery, H., Camargo, C. A., Conlon, C., Beck, K. L., Kruger, M. C., & von Hurst, P. R. (2016). Vitamin D and autism spectrum disorder: A literature review. Nutrients, 8(4), 1-35. https://doi.org/10.3390/nu8040236

Saad, K., Abdel-Rahman, A. A., Elserogy, Y. M., Al-Atram, A. A., El-Houfey, A. A., Othman, H. A., Bjørklund, G., Jia, F., Urbina, M. A., Abo-Elela, M., Ahmad, F. A., Abd El-Baseer, K. A., Ahmed, A. E., & Abdel-Salam, A. M. (2018). Randomized controlled trial of vitamin D supplementation in children with autism spectrum disorder. Journal of Child Psychology and Psychiatry, and Allied Disciplines, 59(1), 20–29. https://doi.org/10.1111/jcpp.12652 (Retraction published J Child Psychol Psychiatry. 2019 Jun;60(6):711)

Saad, K., Abdel-Rahman, A., Elserogy, Y., Al-Atram, A., El-Houfey, A., Othman, H., Bjørklund, G., Jia, F., Urbina, M., Abo-Elela, M., Ahmad, F., Abd El-Baseer, A., Ahmed, A., & Abdel-Salam, A. (2019). Retraction: Randomized controlled trial of vitamin D supplementation in children with autism spectrum disorder. Journal of Child Psychology and Psychiatry, and Allied Disciplines, 60(6), 711. https://doi.org/10.1111/jcpp.13076

Song, L., Luo, X., Jiang, Q., Chen, Z., Zhou, L., Wang, D., & Chen, Ai. (2020). Vitamin D supplementation is beneficial for children with autism spectrum disorder: A meta-analysis. Clinical Psychopharmacology and Neuroscience, 18(2), 203-213. http://doi.org/10.9758/cpn.2020.18.2.203

Sonuga-Barke, E., John Wiley & Sons. (2019). Retraction. Randomized controlled trial of vitamin D supplementation in children with autism spectrum disorder. The Journal of Child Psychology and Psychiatry, 60, 711. https://doi.org/10.1111/jcpp.13076

Wagner, C. L., & Greer, F. R. (2008). Prevention of rickets and Vitamin D deficiency in infants, children, and adolescents. American Academy of Pediatrics, 122(5). 1142-1152. https://doi.org/10.1542/peds.2008-1862

Citation for this article:

McHugh, C. L., & Zane, T. (2021). Vitamin D supplementation: Is there science behind that? Science in Autism Treatment, 18(11).

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