Study: Low Vitamin D Levels During Pregnancy Increase Risk for ADHD Diagnosis in Children
Though many nutritional deficiencies are in decline worldwide, vitamin D deficiency remains prevalent, especially among pregnant women. This Finnish study provides the strongest evidence to date linking developmental vitamin D deficiency and ADHD diagnoses in offspring.
January 29, 2020
Low vitamin D levels during pregnancy increase the risk of ADHD diagnosis in childhood, according to a study from The Journal of the American Academy of Child & Adolescent Psychiatry. This is the first study to investigate the impact of maternal vitamin D levels on formally diagnosed cases of ADHD in children.1
Researchers identified many covariates associated with ADHD in offspring, including maternal age, self-reported smoking, socioeconomic status, immigrant status, and substance abuse. Additionally, paternal and maternal ADHD diagnosis and psychopathology were associated with ADHD, as were offspring gestational age and weight for gestational age (WGA). Even after controlling for all of these covariates, the results of this study demonstrate a significant relationship between lower maternal vitamin D and ADHD diagnosis in children.1
The nationwide, population-based, case-control study surveyed 1,067 participants with ADHD and 1,067 control participants. All participants were born in Finland between 1998 and 1999, and all diagnostic data is from the Care Register for Health Care (CRHC), which contains all public and private inpatient and outpatient diagnoses after January 1, 1998. Participants in the ADHD group were diagnosed using the International Statistical Classification of Diseases and Related Health Problems (ICD-10) criteria, and diagnoses were based on ICD criteria for hyperkinetic disorder. The number of patients diagnosed with ADHD in this study is very low, as ADHD is still not a common diagnosis in Finland. Participants in the control group did not have a diagnosis of ADHD, conduct disorder (as conduct order is commonly a misdiagnosis for ADHD), or severe intellectual disability.
Researchers determined maternal vitamin D status by retrieving samples of maternal sera from the Finnish Maternity Cohort (FMC), which collects data on virtually every pregnancy in Finland with the informed consent of patients. After being absorbed through the skin or from ingested food, vitamin D metabolizes into 25-hydroxyvitamin D [25(OH)D], which can be measured to determine a participant’s vitamin D level. Researchers utilized quantitative immunoassay to calculate maternal vitamin D status during the first trimester of pregnancy.
Across the board, researchers reported finding very low maternal vitamin D levels.1 This finding was impacted by a few important factors. First, researchers collected data from pregnancies prior to 2004, when Finland issued a national recommendation for vitamin D supplementation for pregnant women. Additionally, Finland is one of the northernmost countries in Europe: Even southern Finland receives only 6 hours of sunlight a day during the winter months, and northern Finland (above the arctic circle) is in a state of perpetual darkness from December to January.2 Thus, seasonal impacts on vitamin D levels were extremely prevalent throughout in this study, and researchers controlled for these findings.
This study worked alongside the Finnish Prenatal Study of ADHD, which compiled information from all live births between 1991 and 2005, and reported any ADHD diagnosis from the CHRC through 2011. Study participants with ADHD had to receive a diagnosis before they turned 14; the average age of diagnosis in this study was 7.3 years old.1 Thus, data from patients with late ADHD diagnoses are excluded from this study. Additionally, all participants with ADHD in this study had been referred to specialized services, and the researchers concede that the ADHD group “likely represents the more severe ADHD cases.”1
Two prior studies have investigated maternal vitamin D deficiency during pregnancy and ADHD symptoms
in offspring, but these studies are based on parent or teacher ratings rather than formal ADHD diagnostic data. Thus, more studies examining maternal vitamin D levels and ADHD diagnosis rates that rely on objective, diagnostic criteria are necessary for complete confidence in these findings.
Before the study, researchers hypothesized that low maternal vitamin D levels during early gestation would be associated with increased odds of children receiving an ADHD diagnosis. Despite the lack of research on this specific correlation, it is reasonable to consider vitamin D’s role in development of ADHD for a number of reasons. Vitamin D is known to affect brain function through regulation of calcium signaling, maturation, and growth, to name a few. Additionally, recent studies have uncovered vitamin D’s important role in the development of the central nervous system. Other studies have found that developmental vitamin D deficiency is associated with a range of persistent neurochemical and behavioral outcomes – from schizophrenia to autism spectrum disorder. Thus, it is critical to examine maternal vitamin D levels and their impact on fetal brain development.
Though many nutritional deficiencies are in decline around the world, vitamin D deficiency remains prevalent. In fact, vitamin D deficiency is especially prevalent among pregnant women. This study provides the strongest evidence to date linking developmental vitamin D deficiency and offspring ADHD, and, if its findings are replicated, could have serious public health implications in regards to vitamin D supplementation and lifestyle behaviors during pregnancy.
1Sucksdorff, M., Brown, A., Chudal, R., Surcel, H., Hinkka-Yli-Salomäki, S., Cheslack-Postava, K., … Sourander, A. (2019). Maternal Vitamin D Levels and the Risk of Offspring Attention-Deficit/Hyperactivity Disorder. Journal of the American Academy of Child and Adolescent Psychiatry. https://doi.org/10.1016/j.jaac.2019.11.021