Lack of Sun, Lack of Balance: The Link Between Vitamin D and Depression

Depression is a very common illness and may become the leading cause of disability worldwide. Researchers are studying various factors involved in its development, including vitamin D, which has important functions in the brain. There is evidence that low levels of this vitamin are associated with depression, but it is still unclear whether supplementing it helps in prevention or treatment. More studies are still needed.

Depression is a very common illness worldwide. It can affect people of any age and is associated with other physical and mental illnesses. According to the World Health Organization, about 5% of adults have depression, and this number is even higher among people over 60.

Depression interferes with daily life, impairs emotional well-being, affects relationships, and reduces productivity at work. Estimates show that, by 2030, it may become the leading cause of disability on the planet. Furthermore, after the COVID-19 pandemic, the number of cases increased significantly.

Researchers are seeking to better understand what causes depression. Currently, it is known that it does not appear for a single reason. Instead, it results from a combination of factors such as chemical changes in the brain, inflammation, chronic stress, genetics, lifestyle, and traumatic events.

It was once believed that depression was caused solely by an imbalance of substances like serotonin and norepinephrine. However, more recent studies show that antidepressant medications act on various body systems.

They can reduce inflammation, protect neurons from damage, regulate stress hormones, and stimulate factors important for the health and connection of brain cells. Even so, these medications don't always work well for everyone, and many people stop treatment prematurely or maintain symptoms even with correct use.

Therefore, researchers have begun investigating other factors that may contribute to the development of depression. One of them is vitamin D. This vitamin is produced mainly when the skin receives sunlight, but it can also come from food.

In the body, vitamin D undergoes transformations in the liver and kidneys until it becomes active. The active form binds to receptors present in various organs, including the brain. Interestingly, these receptors are located especially in areas that control emotions, mood, and memory.

Vitamin D is involved in several important brain functions. It helps produce substances that protect and strengthen neurons and promotes the creation of new brain connections. Furthermore, it participates in the balance between chemicals that regulate mood, such as serotonin, dopamine, and glutamate. Some studies show that low levels of vitamin D can alter these systems.

Another important point is that vitamin D appears to help control inflammation in the body and reduce damage caused by oxidative stress (a type of cellular damage). These two processes, inflammation and oxidative stress, have frequently been linked to the development and worsening of depression.

A lack of vitamin D can also alter the functioning of the stress-related hormonal axis, which includes the hypothalamus, pituitary gland, and adrenal glands. This system is often dysregulated in people with depression.

Based on this evidence, scientists began testing whether vitamin D supplementation could help people with depression. Some studies show improvement in depressive symptoms with the use of vitamin D, while others have not observed a clear benefit. The results are still mixed.

To better understand this relationship, a systematic review was conducted, a type of study that analyzes many already published studies. The researchers followed international guidelines to ensure scientific rigor and searched thousands of articles. After excluding duplicate or inadequate studies, 66 relevant studies remained.

The overall results of this review show that there is indeed an association between low vitamin D levels and depression, especially in studies that analyzed people at a single point in time.

However, there is still not enough evidence to say for sure whether low vitamin D causes depression or whether depression contributes to lower levels of this vitamin. It is also not yet entirely clear whether taking vitamin D can consistently prevent or treat depression.

Therefore, although there is a strong suspicion of a link between vitamin D and depression, more research is needed, especially long-term studies, to understand whether supplementation can be used as part of treatment or prevention.

READ MORE:

Vitamin D and depression in adults: A systematic review

Vlad Dionisie, Mihnea Alexandru Gaman, Cristina Anghele, Mihnea Costin Manea, Maria Gabriela Puiu, Iulia-Ioana Stanescu-Spinu, Octavian-Ilarian Baiu, Florian Antonescu, Mirela Manea and Adela Magdalena Ciobanu

Biomolecules and Biomedicine. vol. 25 n. 10 (2025) 

DOI: 10.17305/bb.2025.12331

Abstract:

Depression is one of the most prevalent psychiatric disorders and a leading cause of disability worldwide. Although the pathogenesis of depression remains far from fully understood, current research suggests a potential role for vitamin D due to its involvement in brain functioning. Moreover, vitamin D supplementation has shown promising results in the treatment of patients with depression. Therefore, the present study aimed to systematically review the available research investigating the association between vitamin D levels and the onset of depression. This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and the protocol was registered in the PROSPERO database (registration number: CRD42024515918). A search was performed across PubMed/Medline, SCOPUS, and Web of Science databases, yielding a total of 8,052 potentially eligible articles. After the removal of duplicates and ineligible records, and exclusion based on title and abstract screening, 297 original full-text articles were assessed according to the inclusion and exclusion criteria. Ultimately, 66 articles were included in this systematic review. Most of the included studies employed a cross-sectional design (N = 46). Overall, the data analyzed in this review indicate an association between depression and vitamin D serum levels, particularly in studies using cross-sectional designs. Only a few longitudinal studies demonstrated that lower vitamin D levels are associated with an increased risk of developing depressive symptoms or major depressive disorder, highlighting an important research gap. However, it remains to be established through future research whether acute or chronic vitamin D supplementation could have a protective effect against the development of depression.