The Influence of Vitamin D Intake and Status on Mental Health in Children: A Systematic Review

A potential role of vitamin D in some components of mental health is currently suggested, but the analyses are conducted mainly for adults, while for young individuals mental health is especially important, due to its lifelong effects. The aim of the study was to analyze the association between vitamin D intake or status and mental health in children within a systematic review of literature, including both intervention and observational studies. The literature search was conducted according to the PRISMA guidelines and it covered peer-reviewed studies included in databases of PubMed and Web of Science until October 2019. The studies presenting either vitamin D intake, or vitamin D status in human subjects were allowed (excluding subjects with intellectual disabilities, eating disorders and neurological disorders), while for mental health the various methods of assessment and wide scope of factors were included. The bias was assessed using the Newcastle–Ottawa Scale (NOS). The review was registered in the PROSPERO database (CRD42020155779). A number of 7613 studies after duplicate removing were extracted by two independent researchers, followed by screening and assessment for eligibility, conducted by two independent researchers in two steps (based on title and abstract). Afterwards, the full texts were obtained and after reviewing, a number of 24 studies were included. The synthetic description of the results was prepared, structured around exposure (vitamin D supplementation/status) and outcome (components of mental health). The included studies were conducted either in groups of healthy individuals, or individuals with mental health problems, and they assessed following issues: behavior problems, violence behaviors, anxiety, depressive symptoms/depression, aggressive disorder, psychotic features, bipolar disorder, obsessive compulsive disorder, suicidal incident, as well as general patterns, as follows: mental health, level of distress, quality of life, well-being, mood, sleep patterns. The vast majority of assessed studies, including the most prominent ones (based on the NOS score) supported potential positive influence of vitamin D on mental health in children. As a limitation of the analysis, it should be indicated that studies conducted so far presented various studied groups, outcomes and psychological measures, so more studies are necessary to facilitate comparisons and deepen the observations. Nevertheless, vitamin D intake within a properly balanced diet or as a supplementation, except for a safe sun exposure, should be indicated as an element supporting mental health in children, so it should be recommended to meet the required 25(OH)cholecalciferol blood level in order to prevent or alleviate mental health problems.


Introduction
The number of studies analyzing vitamin D status, relevance of its supplementation, as well as a link between this nutrient and clinical outcomes is currently increasing [1]. The knowledge about vitamin D is still broadening [2], but various serum 25-hydroxyvitamin D (25(OH)D) level thresholds are defined by prominent authorities as vitamin D deficiency, namely lower than 30 nmol/L [3,4] and lower than 50 nmol/L [5,6]. The prevalence higher prevalence of hypovitaminosis D than the general pediatric population [33] and that the association observed in adults may be also noticed in children and adolescents [34].
Based on the presented background, the aim of the study was to analyze the association between vitamin D intake or status and mental health in children within a systematic review of literature, including both intervention and observational studies.

Design
The literature search was conducted according to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [35] and it covered peer-reviewed studies included in databases of PubMed and Web of Science until October 2019. The review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (CRD42020155779).

Inclusion and Exclusion Criteria
The included observational studies presented association between vitamin D intake (either from diet or supplementation) and mental health in children. The inclusion criteria were as follows: (1) studies conducted in children/adolescents; (2) studies presenting vitamin D intake (either from diet or supplementation), or vitamin D status assessed (e.g., 25(OH)cholecalciferol blood level); (3) studies presenting mental health, while various methods of assessment (e.g., medical diagnosis, questionnaire) and wide scope of factors associated with mental health were allowed.
The exclusion criteria were as follows: (1) animal model studies; (2) studies presenting influence of maternal vitamin D intake/status on mental health of their offspring; (3) studies presenting influence of broad spectrum of nutrients combined; (4) studies in participants with intellectual disabilities; (5) studies in participants with eating disorders; (6) studies in participants with neurological disorders (e.g., epilepsy).
The studies to be included were to be published in English in a peer-reviewed journal and were allowed to be conducted in any country, with no other criteria based on location or characteristics of the studied sample.

Searching Strategy
The literature searching covered intervention and observational studies included in databases of PubMed and Web of Science until October 2019. The search was based on the potential outcomes, commonly included to the systematic reviews [31]. The applied detailed electronic search strategy is presented in Table 1. As various outcomes were studied, the results of the systematic review were impossible to be reanalyzed as a metaanalysis, so synthetic description of results was prepared and structured around exposure (vitamin D intake/status) and outcome (components of mental health).
Identified studies after duplicate removing were extracted by two independent researchers followed by screening and assessment for eligibility, conducted by two independent researchers in two steps (to verify it separately based on title and in case of included, also based on abstract). If any disagreement appeared it was discussed with other researchers. Meanwhile, potentially eligible studies which were unavailable, were obtained by contacting the corresponding author of the study to ask them for a full text. Finally, the full texts were analyzed by two independent researchers. If any disagreement appeared it was discussed with other researchers. The detailed inclusion procedure is presented in Figure 1. Web of Science (TS=("vitamin D" OR "vitamin D2" OR "vitamin D3" OR "D2" OR "D3" OR "ergocalciferol" OR "cholecalciferol" OR "25-hydroxyvitamin D" OR "3-epi-25 hydroxyvitamin D" OR "calcitriol" OR "dihydroxycholecalciferol") AND TS=("mental health" OR "mental disorders" OR "mental disorder" OR "psychological distress" OR "mood disorder" OR "depression" OR "suicidal" OR "suicide" OR "anxiety" OR "well-being" OR "wellbeing" OR "quality of life" OR "self esteem" OR "self-esteem" OR "self efficacy" OR "self-efficacy" OR "resilience" OR "empowerment" OR "social participation" OR "mental capital" OR "life skills" OR "emotional" OR "psychology" OR "psychosocial" OR "psychiatry") NOT TS=("animal" NOT ("animal" AND "human")))

Data Extraction Procedure
The data extracting was conducted by two independent researchers. If any disagreement appeared it was discussed with other researchers. If any data were missing, they were requested by contacting the corresponding authors of the study to ask them for a In case of one included study, due to the fact that it was presented as an abstract only [36], the manual search for the full text article was conducted to replace abstract by full text [37].

Data Extraction Procedure
The data extracting was conducted by two independent researchers. If any disagreement appeared it was discussed with other researchers. If any data were missing, they were requested by contacting the corresponding authors of the study to ask them for a detailed information. In case of data provided on request, they are referred in Results section as provided on request. The data were extracted based on the common approach to extract the following information: (1) general characteristics of the study, including: authors, design of the study, country or region; studied group; studied period; (2) participants of the study, including: number of participants, sex, age, inclusion and exclusion criteria; (3) assessment of vitamin D intake, or status, including: applied supplementation, or method of assessment of vitamin D status; (4) assessment of mental health, including: method of assessment, applied psychological measure; (5) findings of the study, including: observations described by authors of the study; findings formulated by the authors of the study.
The risk of bias and methodological quality of the included studies was assessed as recommended based on the Cochrane guidelines [38] using the Newcastle-Ottawa Scale (NOS) [39]. The case control studies were assessed, including the following criteria: selection, comparability, and exposure, while cohort studies were assessed, including the following criteria: selection, comparability, and outcome. The total score was described while compared with the following categories: very high (from 0 to 3 points), high (from 4 to 6 points), and low risk of bias (from 7 to 9 points), as it is commonly applied [40].

Intervention Studies
The basic characteristics of the included intervention studies [37,[41][42][43][44][45][46], including design of study, location, studied group and time are described in Table 2. The included intervention studies were conducted in various countries-United States of America [37,45], Nordic countries [43,46], Iran [41,42] and Turkey [44]. Only one study described a single sex sample of adolescent girls [42], while other studies were conducted in a mixed populations of boys and girls of various age [37,41,[43][44][45][46]. Moreover, a majority of intervention studies assessed a specific populations of children with a sickle cell disease [37], attention deficit hyperactivity disorder (ADHD) [41], autism spectrum disorders [44], bipolar spectrum disorders [45] and depression [46], being in some studies compared with control groups. The characteristics of the subjects of the included intervention studies are described in Table 3. The included intervention studies were conducted in samples of various size, differing from 35 [45] to 940 participants [42], while the inclusion and exclusion criteria were formulated to obtain required samples. For the vast majority of studies, the exclusion criteria included any condition that would interfere with planned vitamin D supplementation, including the previously applied supplementation [37,[41][42][43][44], participation in any other study impacting serum 25(OH)cholecalciferol blood level [37], and any disorder interfering with the action, absorption, distribution, metabolism or excretion of vitamin D [45], or required being stably medicated if taking daily supplementation [45].
The exposure, intervention and outcome of the included intervention studies are described in Table 4. The included studies presented various models of intervention, mainly conducted for 3 months [37,41,43,44,46], but also 2 months [45] and 9 weeks [42], while applied vitamin D doses differed from 25 µg per day [41] to 1250 µg per week (179 µg per day) [42,44]. The observed outcomes were associated with depressive symptoms/depression [42,45], aggressive disorder [42], suicidal incident [45], as well as general patterns, as follows: mental health [41,43], quality of life [37], well-being [46], mood [45,46], sleep patterns [44], which were assessed while using dedicated psychological measures.   [45] 35 (15) 12.3 ± 3.2 for bipolar spectrum disorder group 11.9 ± 3.6 for control group Inclusion: children and adolescents from Child and Adolescents NeuroDevelopment Initiative (CANDI) at the University of Massachusetts Medical School; aged 6-17 years; being able ingest the vitamin D3 orally; the screen visit Young Mania Rating Scale (YMRS) score ≥ 8 and the Clinical Global Impressions-Severity Score (CGI-S) ≥ 3 (for bipolar spectrum disorder group); if taking psychotropic medications, or daily multivitamin or vitamin supplement, stably medicated (same dose for 4 weeks prior to enrolment and willing to do it within the study) Exclusion: history of an uncontrolled general medical disorder; history of neurological illness, schizophrenia, or psychosis; history of head trauma with loss of consciousness; substance dependence; suicidal or homicidal ideation; contraindications to magnetic resonance imaging; disorder that would interfere with the action, absorption, distribution, metabolism or excretion of vitamin D3, that might pose a safety concern, or interfere with the accurate assessment of safety and efficacy; axis I diagnosis or a family history of a mood disorder in a first degree (for control group)  The findings presented in the intervention studies are described in Table 5, based on the data presented by authors of the refereed studies as the most important ones. Table 5. The findings presented in the intervention studies included to the systematic review.

Ref.
Observation Conclusion [37] In subjects with SS sickle cell disease, significant reductions in pain, fatigue, and depressive symptoms and improved upper-extremity function were observed. In healthy subjects, significant reductions in fatigue and improved upper-extremity function were observed.
Daily high-dose vitamin D supplementation for African American children with SS sickle cell disease improved HRQL. [41] The mean scores of the SDQP and SDQT showed a significant difference in the two groups after intervention.
Vitamin D supplementation improves some behavioral problems. [42] There was a significant reduction on mild, moderate, and severe depression score. However, vitamin D supplementation had no significant effect on aggression score.
Results suggest that supplementation with vitamin D may improve depressive symptoms among adolescent girls, as assessed by questionnaire, but not aggression score. [43] Multivariate data analysis showed that participants with low vitamin D status scored worse on the Tower of London tests and the more difficult sub-tasks on the Tower of Hanoi tests. They also had a tendency to report higher frequency of externalizing behavior problems and attention deficit.
The study indicates that vitamin D status in adolescents may be important for both executive functioning and mental health. [44] In ASD patients, there was a significant negative correlation between serum 25(OH)D levels and the night waking subscale (r = −0.301, p = 0.019). In control patients, there was a significant negative correlation between serum 25(OH)D levels and daytime sleepiness subscales (r = −0.269, p = 0.038).
The results indicate that it may be suitable to use 25(OH)D replacement therapy in ASD patients and healthy individuals with sleep disturbances. [45] Following an 8 week vitamin D3 supplementation, in BSD patients, there was a significant decrease in YMRS scores (t = −3.66, p = 0.002, df = 15) and CDRS scores (t = −2.93, p = 0.01, df = 15).
Following an 8 week open label trial with vitamin D3 supplementation, patients with BSD exhibited improvement in their mood in conjunction with their neurochemistry. [46] Basal 25(OH)D levels correlated positively with well-being (p < 0.05). After vitamin D supplementation, well-being increased (p < 0.001) and there was a significant improvement in eight of the nine items in the vitamin D deficiency scale: depressed feeling (p < 0.001), irritability (p < 0.05), tiredness (p < 0.001), mood swings (p < 0.01), sleep difficulties (p < 0.01), weakness (p < 0.01), ability to concentrate (p < 0.05) and pain (p < 0.05). There was a significant amelioration of depression according to the MFQ-S (p < 0.05).
This study showed low levels of vitamin D in depressed adolescents, positive correlation between vitamin D and well-being, and improved symptoms related to depression and vitamin D deficiency after vitamin D supplementation.
The characteristics of the participants of the included observational studies are described in Table 7. The included observational studies were conducted in the samples of various size, differing from 36 [51] to 9068 participants [54], while the inclusion and exclusion criteria were formulated to obtain homogenic samples to obtain the aim of the study. In case of some studies, the exclusion criteria included the previously applied vitamin D supplementation [48,49,52].
The findings presented in the observational studies are described in Table 9, based on the data presented by authors of the refereed studies as the most important ones.

Ref
Authors       [47] Vitamin D deficiency was associated with an adjusted 6.0 (95% CI: 3.0, 9.0) and 3.4 (95% CI: 0.1, 6.6) units higher Child Behavior Checklist and Youth Self-Report externalizing problems scores, respectively, and an adjusted 3.6 (95% CI: 0.3, 6.9) units higher Child Behavior Checklist internalizing problems scores. The prevalence of clinical total externalizing problems was 1.8 (95% CI: 1.1, 3.1) times higher in children with vitamin D deficiency than that in children without vitamin D deficiency.

Ref. Observation Conclusions
Vitamin D deficiency in middle childhood is related to behavior problems in adolescence.
[48] Serum 25(OH)D levels were positively correlated with ADL score in children with stable asthma, and negatively correlated with MRC score.
Increased serum 25(OH)D levels reflect good QoL in children with stable asthma. Low serum levels of vitamin D are independently associated with anxiety among children and adolescents on dialysis, which needs to be confirmed in future experimental and clinical studies. [50] Patients with depressive disorder had lower concentrations of 25(OH)D (p < 0.005) than control participants, in both male and female cohorts. However, serum 25(OH)D concentration did not significantly correlate with depressive symptoms.
Adolescents with depressive disorder have markedly lower serum 25(OH)D concentrations than control patients. This relationship is positively associated with disease progression, suggesting possible nutritional intervention measures for neuroprotection. [51] There was no difference between serum vitamin D concentrations in participants from non-mood control, major mood disorders, and bipolar disorder groups.
There was no difference between serum vitamin D concentrations in participants from non-mood control, major mood disorders, and bipolar disorder groups. [52] Vitamin D levels were lower in patients diagnosed with OCD (15.88 ± 6.96 ng/mL) when compared to healthy controls (18.21 ± 13.24 ng/mL), but the difference was not statistically significant (p = 0.234). A negative correlation was found between serum 25(OH)D levels and obsession scale scores in CYBOCS.
The vitamin D levels of newly diagnosed OCD cases were lower than that of healthy controls; however, the difference was not statistically significant. The study does not support presence of a significant association between serum vitamin D levels and OCD. [53] Significantly lower levels of vitamin D in the patient group compared to control group (p < 0.001) were observed. Vitamin D deficiency can play a role in the etiology of OCD. Table 9. Cont.

Ref.
Observation Conclusions [54] There were inverse associations between 25(OH)D concentrations and the subscales emotional problems, peer relationship problems and the total difficulties score in both genders after adjustment for potential confounders. The strongest associations were observed in the older subsample for parent-ratings in boys and self-ratings in girls. In the younger subsample the associations were less strong and no longer evident after adjustment for potential confounders such as migration background, socioeconomic status and frequency of playing outside.
Based on the large-scale cross-sectional study in a German population-based sample of children and adolescents inverse associations between 25(OH)D concentrations and both parent-and self-rated SDQ scores of the total difficulties scale and different subscales with the strongest association in the subsample aged 12-18 years for both genders were detected. [55] No relationships between mental health parameters (type or total) and vitamin D status were observed.
The influence of vitamin D status on mental health may extend beyond mental health disease type to disease severity, because disease expression may change with overall child development.
[56] Negative correlation was found between the vitamin D levels and depression score in the group with depression (r = −0.368; p = 0.03).
Even if clinical depression is absent, the frequency of depressive symptoms is increased with decreased vitamin D levels, independent of other factors. Maintaining vitamin D support during adolescence, as with the first year of life, is necessary for both the prevention and treatment of depression. [58] The prevalence of self-reported anger, anxiety, poor quality sleep, sadness/depression, and worry was significantly lower in vitamin D sufficient participants compared with their other counterparts. The odds of reporting anger, anxiety, poor quality sleep, and worry, increased approximately 1. Some psychiatric distress such as anger, anxiety, poor quality sleep, depression, and worry are associated with hypovitaminosis D in adolescents. Table 9. Cont.
The 25(OH)D insufficiency was associated with depressive symptoms in this cohort of youth with CF. Future rigorous studies investigating vitamin D and depression in CF are warranted with larger sample sizes using confirmatory methods to diagnose depressive disorders. [60] The 25(OH)D did not differ in girls with MDD compared to controls, even after adjusting for BMI, lean mass and bone age. Vitamin D levels were not significantly different in MDD compared to controls even after adjusting for BMI. Vitamin D was significantly higher in girls with MDD as compared to controls (MDD: 33.5 ± 8.1 versus healthy controls: 22.5 ± 8.0 ng/mL; p < 0.001), and this difference remained statistically significant after adjusting for BMI (p = 0.001).
Vitamin D was significantly higher in girls with MDD as compared to controls, but did not differ for other comparisons. [61] Adolescents with psychotic features had lower vitamin D levels than those without (20.4 ng/mL vs. 24.7 ng/mL; p = 0.04, 1 df). The association for vitamin D deficiency and psychotic features was substantial (OR 3.5; 95% CI 1.4-8.9; p < 0.009).
Vitamin D deficiency and insufficiency are both highly prevalent in adolescents with severe mental illness. [62] Higher 25(OH)D3 concentrations were weakly associated with lower risk of prosocial problems (fully adjusted OR 95% CI 0.85 (0.74, 0.98)). Serum 25(OH)D3 or 25(OH)D2 concentrations were not associated with other subscales of SDQ or total difficulties score after adjusting for confounders and other measured analytes related to vitamin D.
The findings do not support the hypothesis that 25(OH)cholecalciferol status in childhood has important influences on behavioral traits in humans. [63] Higher concentrations of 25(OH)D3 assessed at mean age 9.8 years were associated with lower levels of depressive symptoms at age 13

Summary
The summary of observations and conclusions for included studies of association between vitamin D and mental health, with the total NOS score are described in Table 10. It was observed that for the vast majority of included studies, both intervention and observational ones, the results supported beneficial association. Only in case of 2 studies, no effect of vitamin D was stated for bipolar disorder and major depressive disorder [51] and mental health (assessed using DSM-V criteria) [55]. In case of three studies the effect of vitamin D was inconclusive, as it was observed only for some of applied analysis [50,60] or depending on the studied component of obsessive compulsive disorder [52]. However, while the total NOS score is taken into account, it should be indicated that all the studies of low risk of bias support the positive effect of vitamin D [47,62,63]. Table 10. The summary of observations and conclusions for the included studies of association between vitamin D and mental health, with the total Newcastle-Ottawa Scale (NOS) score.

Ref.
Potential Influence of Vitamin D

Results Supporting/Inconclusive/Not Supporting Positive Association between
Vitamin D Intake and Mental Health * Quality ** [37] Reduced pain, fatigue, and depression, as well as improved upper-extremity function Supporting 3 [41] Reduced some behavioral problems Supporting 5 [42] Reduced depression Supporting 4 [43] Reduced externalizing behavior problems and attention deficit and improved cognition Supporting 3 [44] Reduced sleep disturbances Supporting 4 [45] Reduced depression and mania Supporting 4 [46] Reduced depression, irritability, tiredness, mood swings, sleep difficulties, weakness and pain, as well as improved well-being and ability to concentrate Supporting 3 [47] Reduced externalizing and internalizing problems Supporting 7 [48] Improved quality of life Supporting 3 [49] Reduced anxiety Supporting 5 [50] Reduced/not reduced depression (depending on analysis) Inconclusive 4 [51] No effect on bipolar disorder and major depressive disorder Not supporting 2 [52] No effect on obsessive compulsive disorder, but reduced obsession component Inconclusive 4 [53] Reduced obsessive compulsive disorder Supporting 5 [54] Reduced emotional problems and peer relationship problems Supporting 5 [55] No effect on mental health Not supporting 5 [56] Reduced depression Supporting 3 [57] Reduced distress and improved quality of life Supporting 5 [58] Reduced anger, anxiety, depression and worry, as well as improved quality of sleep Supporting 5 [59] Reduced depression Supporting 4 [60] Reduced/not reduced depression (depending on analysis) Inconclusive 5 [61] Reduced psychotic features Supporting 5 [62] Reduced prosocial problems Supporting 8 [63] In longer term reduced depression Supporting 7 * Supporting-vitamin D associated with lower risk of mental health problems; not supporting-vitamin D not associated with lower risk of mental health problems; inconclusive-no clear association between vitamin D and risk of mental health problems; ** total score for the NOS.

Discussion
In spite of the fact that studies of association between vitamin D and mental health present various studied groups, outcomes and psychological measures, the observed results are consistent and they suggest potential beneficial effect of vitamin D blood level or applied supplementation on mental health. Taking this into account, it may be indicated that regardless of the studied group and studied effect associated with mental health, the vitamin D is crucial for mental health.
The association between vitamin D and mental health was so far studied mainly for depression or depressive symptoms [23][24][25][26][27][28][29] and some potential mechanisms explaining the influence of vitamin D were supposed [64]. Vitamin D has potential to cross the blood-brain barrier, to activate receptors in brain cells and to exert its direct impact in the central nervous system [65]. Moreover, there is some evidence for the link between vitamin D and Vitamin D Receptors (VDRs) and the regulation of human behavior, that is strongly suggested by the presence of VDRs in such brain areas as cortex, cerebellum and limbic system [66]. At the same time, Eyles et al. [67] reported that the mechanism potentially important in neuroendocrine functioning may be associated with the VDRs in the hypothalamus. However, it should be also mentioned that VDR genes are polymorphic and their variations occur frequently, what can cause various vitamin D-related dysfunctions [68].
Moreover, studies in animal models indicated potential anti-inflammatory effects of vitamin D administration in hippocampus and hypothalamus and its modulating effects on brain-derived neurotropic factor (BDNF) [65] which may also play a role. Simultaneously, the role of vitamin D may be attributed to its neuroprotective role in the brain which is reflected in modulating neurotrophic signaling [69], and in regulating inflammation by inhibiting proinflammatory cytokines [70].
Taking into account the potential mechanisms described above and the results of the recent studies suggesting beneficial effect of vitamin D on mental health, this area is indicated within the current research perspectives associated with vitamin D [71]. Regardless of the fact, that biological mechanisms linking vitamin D and mental health are still not fully understood [72], it should be indicated that vitamin D may have beneficial effects, which is important considering high prevalence of mental health problems which is not decreasing, despite a substantial increases in the provision of treatment [73]. Taking this into account, improving vitamin D status by applying adequate intake either within a properly balanced diet or as a supplementation, may be beneficial also for the prevention and treatment of mental health problems in children.
The included studies analyzing the association between vitamin D intake or status and mental health in children assessed various aspects of mental health, so based on the presented observations, it may be suggested that vitamin D is associated with the broad area of mental health with all its elements. However, the limitations of the presented systematic review must be also described. The most important fact results from the limited number of studies published so far, while included studies presented various studied groups, outcomes and psychological measures, so more studies are necessary to deepen the observations. Moreover, since the studies assessed a wide range of possible effects, meta-analysis was impossible [74], so only the systematic review was conducted. Last but not least, only peer-reviewed studies included in databases of PubMed and Web of Science are presented in the systematic review which may have caused that some interesting results are not presented.
At the same time, it should be indicated that some researchers suggest the possible reverse causality in the association between vitamin D and mental health [75]. It results from the fact that some individuals with mental health problems, including depression, may avoid outdoor activity and have poor appetite, resulting in reduced sunlight exposure and consequently reduced endogenous vitamin D synthesis, as well as reduced dietary vitamin D intake [76]. At the same time, they may have increased demand for vitamin D resulting from the disturbed calcium homeostasis [64] observed in patients with mental health problems [77].
Based on the prepared systematic review, vitamin D intake within a properly balanced diet or as a supplementation, except for a safe sun exposure, should be indicated as an element supporting mental health in children, so it should be recommended to meet the required 25(OH)cholecalciferol blood level in order to prevent or alleviate mental health problems.

Conclusions
The vast majority of assessed studies, including the most prominent ones (based on the NOS score) supported potential positive influence of vitamin D on mental health in children. Vitamin D intake within a properly balanced diet or as a supplementation, except for a safe sun exposure, should be indicated as an element supporting mental health in children, so it should be recommended to meet the required 25(OH)cholecalciferol blood level in order to prevent or alleviate mental health problems.