Vitamin D and Depression (2020)
Daily morning and afternoon exposure to bright light might actually be more important to reducing depression than direct vitamin D supplementation. Low vitamin D might just be an indicator that you are not getting enough sunlight. Sunlight also affects melatonin and serotonin levels, and synchronizes your Circadian rhythm. Not sure why that article doesn't talk about Seasonal affective disorder (SAD), and how bright light therapy is considered an effective treatment for it.