Serum 25-Hydroxyvitamin D Concentrations Are Associated with Mental Health and Psychosocial Stress in Young Adults

We aimed to test the hypothesis that serum 25-hydroxyvitamin D3 (25(OH)D) concentration is associated with mental health and life stress measures in young adults and investigate gender and racial disparities in these associations. This study comprised 327 black and white participants. Depression, trait anxiety, perceived stress, and hostility were measured by the following validated instruments: Beck Depression Inventory (BDI), State-Trait Anxiety Inventory (STAI), Perceived Stress Scale (PSS), and Cook–Medley Hostility Scale (CMHS). Linear regression was used to estimate correlations between serum 25(OH)D concentration and mental health measurements in the total population and in subgroups stratified by gender and race. In this sample (28.2 ± 3.1 years, 52% female, 53% black), serum 25(OH)D concentration was negatively related to BDI, STAI, PSS, total CMHS score, and the majority of CMHS subscale scores (p-values < 0.05). Stratified by gender, most of these associations remained significant only in women (p-values < 0.05). Stratified by race, higher 25(OH)D concentrations in white participants were significantly related to lower BDI, STAI, PSS, and CMHS-cynicism subscales (p-values < 0.05); 25(OH)D concentrations in the black participants were only inversely associated with CMHS and most CMHS subscales (p-values < 0.05) but not with BDI, STAI, and PSS. We present novel findings of consistent inverse relationships between serum 25(OH)D concentration and various measures of mental health and life stress. Long-term interventional studies are warranted in order to investigate the roles of vitamin D supplementation in the prevention and mitigation of depression, anxiety, and psychological stress in young adults.


Introduction
Mental health is an important dimension of health, affecting the overall quality of life, and mental disorders impose significant economic, social and public health burden [1]. Mental disorders not only compromise the quality of life, but also are important risk factors for physical/somatic diseases. Studies suggest that depression is associated with inflammation [2] and cardiovascular disease [3]. Higher perceived stress has been related to worse outcomes of aging [4] and immunity [5]. In addition to depression, other areas of mental health and stress can affect disease. For example, anxiety was significantly associated with coronary artery calcification [6], and hostility is related to insulin resistance and inflammation [7].
Many studies which examined plasma levels of vitamin D and association with mental health disorders have focused upon depression. The outcomes of these studies have been mixed.
Inverse association between circulating vitamin D concentration and depression has been observed in adults in New Zealand [8], Australia [9], Finland [10], and the U.S. elderly [11].
Other studies found that the association was not statistically significant among elderly in Italy [12], Netherlands [13], nor adults in Denmark [14] and the U.S. [15].
The relationship between serum 25(OH)D concentration and anxiety symptoms has been assessed in a few studies, and the associations were mostly not significant [9,10,14,16].
However, those findings may be limited by the fact that in most studies, the anxiety measures were limited and typically were subscales of depression in questionnaires [9,10,14,16,17]. The association between vitamin D and perceived stress or hostility is also under-studied. Only one study found serum 25(OH)D concentration inversely associated with perceived stress. The study involved Korean female elders, and perceived stress was characterized as a dummy variable based on a single question [18].
The majority of the studies conducted to date involved the elderly, and evidence is scarce in young adults, especially in the United States. Therefore, we aimed to test the hypothesis that serum 25(OH)D concentration is associated with mental health and life stress measurements including depression, trait anxiety, perceived stress and hostility of young adults, and to investigate sex and racial disparities in these associations.

Participants
A total of 327 black and white participants (28.2 ± 3.1 years, 48% male, 53% black) from the southeastern region of the U.S. were included in this study. The recruitment and evaluation of participants have been described in details elsewhere [19]. General characteristics, socioeconomic status (SES) and mental health measurements were obtained by questionnaires.
Serum samples were processed for serum 25(OH)D concentrations. The Institutional Review Board at the Augusta University gave approval for the study (IRB#611084-10, May 26, 2020) and informed consent of each participant was obtained.

Vitamin D measurement
Serum 25(OH)D concentrations were determined from fasting blood using an enzyme immunoassay (Immunodiagnostic Systems, Fountain Hills, AZ) according to the manufacturer's specifications. Analytical reliability of the 25(OH)D assays was monitored through participation in DEQAS (Vitamin D External Quality Assessment Scheme) and was deemed acceptable. The intra-and interassay coefficient of variations for serum 25(OH)D were 5.6 and 6.6%, respectively.

Beck Depression Inventory
Beck depression inventory (BDI) was originally developed in 1961 to identify the presence and severity of depressive symptoms [20]. It has been well validated in normal and psychiatric populations [21]. All subjects were required to complete the self-report questionnaire, which contains 21 items. These items relate to the feelings of irritability, guilt, punishment, and physical symptoms such as fatigue, weight loss and lack of interest in sex. Each item is scored on a scale value of 0 to 3. Theoretically, the total score of BDI ranges from 0 to 63, and higher scores indicate more severe depressive symptoms.

State-Trait Anxiety Inventory
Anxiety was measured using the State-Trait Anxiety Inventory (STAI) from Y-2 [22]. Anxiety can be differentiated into state anxiety and trait anxiety. In this study, we measured trait anxiety, which is considered an enduring characteristic that refers to relatively stabilizing individual differences that characterize people's anxiety or a general feeling of anxiety [22]. This inventory has 20 items. All items are rated on a 4-point scale weighted from one to four. The total score for trait anxiety is the total of each item. Higher scores indicate greater anxiety.

Perceived Stress Scale
Perception of stress was measured by the Perceived Stress Scale (PSS), which contains 10 items, and each item has five response options weighted from zero to four [23]. PSS is one of the most widely used psychological instruments for measuring nonspecific perceived stress.

Hollingshead Social Status
Hollingshead Four-Factor Social Status Index was calculated on the basis of parental education level, employment status, and occupation; a higher value indicates higher SES [25]. The Hollingshead parental education level is rated on a 7-point scale that lists the highest grade completed, and the occupational prestige is rated on a 9-point scale. SES was then calculated by multiplying the occupation scale value by a weight of 5 and the education scale value by 3 and summing the products. Hollingshead Index scores range from 8 to 66.

Statistical analysis
The general characteristics of the subjects are presented as mean ± standard deviation (SD) for

Participant Characteristics
Among 327 participants, the mean serum 25(OH)D concentration was 59.2 ± 26.1 nmol/L. We compared general characteristics among the four groups defined by sex and race. Age, 25(OH)D concentration, SES and CHMS among the four groups were significantly different (p-value < 0.05) ( Table 1).

Adjusted associations between mental health measurements and serum 25(OH)D concentrations
In the base models, as shown in Table 2

Discussion
In this study, we found that among U.S. young adults serum 25(OH)D concentrations were significantly related with lower scores on the BDI, STAI, PSS, CMHS and most CMHS subscales (except social aversion) after accounting for age, sex, race and SES.
The associations between 25(OH)D concentration and mental health scales were generally consistent across different mental health domains. Therefore, it is possible that those mental health domains may partially share common pathways linking them to vitamin D levels.
Vitamin D receptors (VDR) and the vitamin D activating enzyme 1α-hydroxylase are present in the human brain [26], and VDR knockout mice have exhibited depressive behaviors [27]. Evidence also shows that 25(OH)D can cross the blood-brain barrier, and 25(OH)D receptors exist in the central nervous system (CNS) [28]. Vitamin D may also relate to mental health through regulation of levels of brain-derived neurotrophic factor (BDNF), which is a protein encoded by the BDNF gene. BDNF deficiency has been associated with age-dependent impairment in spatial learning [29], neurodegeneration [30], cognitive dysfunction [31], as well as with depression [32][33][34]. Vitamin D supplementation may increase BDNF concentration in the hippocampus [35] -a critical brain region for emotion regulation; neural stem cells treated with vitamin D have shown increased expression of BDNF [36].
Inflammation is correlated with mental health. Proinflammatory cytokines can induce depressive symptoms by affecting neurotransmitter metabolism, impairing neuronal health, and altering brain activity in mood-relevant brain regions [37]. in adults with high inflammation levels [38]. Another review noted that vitamin D supplementation can robustly reduce TNF-α and IL-6, but not other cytokines, yet TNF-α and IL-6 were the two cytokines most robustly associated with depression in a meta-analysis [39].
Oxidative stress has been linked to both depression and anxiety. Oxidative stress is increased in depressive subjects [42,43] and has been shown to increase anxiety in animal behavioral models [44]. Indeed, it has been proposed that products of oxidative stress have potential to serve as parameters for measuring and predicting of depression status as well as for determining the effectiveness of administrated antidepressants [45]. Vitamin D supplementation is also related to reduced oxidative stress markers in several human studies [46]. Vitamin D treatment is able to reduce the apoptosis-related gene expression, prevent the loss of mitochondrial potential and the consequent cytochrome C release and caspase activation [47].
In female older adults, while this association was not significant among male participants [18].
In addition to sex differences, we also observed differences by race in the associations between mental health and serum 25(OH)D concentrations. Lower levels of 25(OH)D were associated with increased depression, anxiety and stress among white participants, but were more associated with hostility measures among blacks. These differences suggest possible differences  [48,49]; thus, seen in this context, experiences of hostility or hostile attribution might be considered more sensitive indicators of problems in the mental health domain. However, while older literature [49] has suggested this possibility, more recent work has shown that, in fact, higher burden of depressive symptoms may be present among black compared to white adultsespecially among older adults [50]. Therefore, it is clear overall that further research is required to address racial differences and disparities in mood outcomes, and predictors therein.
To the best of our knowledge, this study is the first to analyze the association between

Conclusion
We observed consistent relationships between lower serum 25(OH)D concentrations and various measures of psychosocial stress and poorer mental health in a large sample of community-based young adults. Future work might address whether vitamin D supplementation and optimization of 25(OH)D levels could be potential modalities for prevention and/or amelioration of psychological distress in young persons.
Funding: This research is supported by 1R01HL131674-01.