Previous cross-sectional and case–control studies have proposed that decreased vitamin D levels are positively correlated with the risk of suicidality in adults. However, limited studies have examined the association between vitamin D and suicidality in adolescents. This study aimed to investigate the relationship between serum vitamin D and suicidality risk among early adolescents.

Data were obtained from a Chinese early adolescent cohort. In this cohort, seventh-grade students from a middle school in Anhui Province were invited to voluntarily participate in the baseline assessments and provide peripheral blood samples (in September 2019). The participants were followed up annually (in September 2020 and September 2021). Serum 25-hydroxyvitamin D [25(OH)D] and vitamin D–related single-nucleotide polymorphisms at baseline were measured in November 2021. Traditional observational and Mendelian randomization (MR) analyses were performed to examine the relationship between serum 25(OH)D at baseline and the risk of baseline and incident suicidality (i.e., suicidal ideation [SI], plans and attempts).

Traditional observational analysis did not reveal a significant linear or non-linear association of serum 25(OH)D concentration with the risks of baseline and 2-year incident suicidality in the total sample (P > .05 for all). Sex-stratified analysis revealed a non-linear association between the 25(OH)D concentration and the risk of baseline SI in women (Poverall = .002; Pnon-linear = .001). Moreover, the risk of baseline SI in the 25(OH) insufficiency group was lower than that in the 25(OH) deficiency group in the total sample (odds ratio [OR] = 0.69, 95% confidence interval [CI] = 0.51–0.92, P = .012). This difference remained significant in women (OR = 0.59, 95% CI = 0.40–0.87, P = .008) but not in men (OR = 0.78, 95% CI = 0.53–1.15, P = .205). Additionally, both linear and non-linear MR analyses did not support the causal effect of serum 25(OH)D concentration on the risk of baseline, 1-year and 2-year incident suicidality (P > .05 for all).

This study could not confirm the causal effect of vitamin D on suicidality risk among Chinese early adolescents. Future studies must confirm these findings with a large sample size.

To explore the cross-sectional and longitudinal association between vitamin D and depressive symptoms across early adolescence.

This longitudinal study included 1607 early adolescents [mean (s.d.) age, 12.49 years; 972 (60.5%) males] from the Chinese Early Adolescents Cohort, recruited from a middle school in Anhui Province and followed up annually (2019–2021). Serum 25(OH)D levels were measured in both 2019 and 2021. Self-reports on depression were assessed at each of three time points from 2019 to 2021.

In the whole sample, higher baseline serum 25(OH)D levels were linked with a lower risk of cumulative incident depression within two-year follow-ups (adjusted RR = 0.97, 95% CI 0.94–0.99) and the increasing trajectory of depression symptoms across the three waves (adjusted RR = 0.97, 95% CI 0.95–0.99). Baseline vitamin D deficiency (VDD) (adjusted RR = 1.50, 95% CI 1.10–2.05) were associated with an increased risk for the increasing trajectory of depression symptoms across the three waves. Remitted VDD was positively related to one dichotomous depression symptoms across three waves (adjusted OR 2.15, 95% CI 1.15–4.01). The above-mentioned significant association was also found in males. Additionally, baseline VDD (adjusted OR 1.59, 95% CI 1.04–2.44) and persistent VDD (adjusted OR 1.58, 95% CI 1.02–2.60) were linked to an increased risk of having two dichotomous depression symptoms only in males.

Our results highlight a prospective association between baseline vitamin D and depression risk in early adolescents. Additionally, a male-specific association between vitamin D and depression risk was observed. Our findings support a potential beneficial effect of vitamin D supplementation in reducing depression risk in early adolescents.