Abstract/Summary

The role of vitamin D in depression has received considerable attention in recent years, due to the significant mortality, disability, and healthcare costs related to depression and vitamin D deficiency. However, the burden of late-life depression is expected to increase in Kuwait as its older population (4% at 65+ years) continues to grow at a disproportionate rate, rising to 17.90% by 2025. In an older population, depression can lead to cognitive impairment, functional decline, lower quality of life, and disability. While a full explanation of the pathophysiology and aetiology of depression has yet to be provided, recent evidence indicates that various biological factors, such as vitamin D deficiency, can affect mood. The first aim of this study is to determine the association between vitamin D supplementation and depressive symptoms in adults, examined in a systematic review and meta-analysis of 10 randomised controlled trials (RCTs) (total participants=3336; median duration=12 months). The second aim is to examine the association between vitamin D deficiency and depression among older adults in Kuwait, using a cross-sectional study (n=237). A validated Geriatric Depression Scale (GDS-15) was adopted to measure symptoms of depression. Additionally, liquid chromatography/mass spectrometry (LCMS/MS) was conducted to measure vitamin D status, while other blood test parameters were also tested (cortisol, blood sugar, parathyroid hormone (PTH), calcium, alkaline phosphatase, phosphorus, and further confounders). Finally, the third aim is to examine the factors associated with vitamin D deficiency in older adults in Kuwait. The findings derived from systematic reviews and meta-analyses indicated a positive association between high vitamin D supplementation (≥4000 IU) and reduced depressive symptoms, but not in the case of lower levels of vitamin supplementation (<4000 IU). Meanwhile, the results of the cross-sectional study indicated that the vitamin D sufficiency group were significantly less likely to exhibit depressive symptoms (88.2%), compared to the participants with mild (36%) or moderate (21%) depression (p<0.001). A low serum vitamin D level was therefore found to be a significant predictor of symptoms of depression among older adults. Vitamin D deficiency was revealed in two-thirds of the participants (n=150, 63%), with a higher prevalence among those who did not receive vitamin D supplements, as opposed to those who did (84% vs. 16%, p=0.001). Moreover, low duration of sun exposure (p=0.011), dark skin pigmentation (p=0.026), and lower caloric intake (p=0.001) were identified as risk factors of vitamin D deficiency. Furthermore, a significant inverse relationship was found between vitamin D levels and PTH levels (p=0.016). Vitamin D supplementation and adequate sunlight exposure are consequently recommended for raising low vitamin D levels in older Kuwaiti adults. The data presented in this thesis could contribute to the fields of neuropsychiatry, dietetics, and community health by demonstrating that the symptoms and severity of depression are associated with serum 25(OH)D levels among older adults in Kuwait. The findings also support the need for vitamin D supplementation and adequate sunlight exposure to raise vitamin D levels in older adults. However, it was deemed important in this thesis to conduct RCTs to determine which vitamin D supplements most effectively prevent and treat depressive symptoms among older adults.