The researchers confirmed that people whose vitamin levels fall below a certain limit (30 nanomoles/liter or less) are more prone to symptoms of depression.
However, the team cautioned that these findings do not necessarily mean that vitamin D deficiency causes depression, but only indicate a correlation between the two. Some long-term studies have yielded conflicting results, highlighting the need for more rigorous research.
Depression affects approximately 5% of adults worldwide and is projected to become the leading cause of health burdens by 2030. Traditional antidepressants help some patients, but often only produce moderate results. Therefore, researchers are exploring other modifiable and safer factors, such as vitamin D.
Vitamin D helps transmit nerve signals, reduces inflammation in the brain, protects cells from damage, and regulates intracellular calcium levels — all of which are important for brain health and mood.
The research team analyzed the results of 66 studies from 31 countries, after reviewing more than 8,000 scientific records. Due to the different methods used to measure vitamin D and the tools used to assess depression, the data were not fully statistically combined; instead, the results were summarized and compared narratively. The quality of each study was also assessed to ensure the reliability of the findings.
In most studies that examined vitamin levels and depressive symptoms simultaneously, researchers found that vitamin D deficiency was associated with increased symptoms.
In studies that followed people long-term, the results were mixed; some studies found an increased risk of depression with vitamin deficiency, and others found no association.
Some studies have shown that this effect may be stronger in women, which calls for specialized research.
Studies differed in how they measured depression and vitamin D levels, making comparisons difficult. Furthermore, some studies did not consider important factors such as sun exposure, weight, or co-existing medical conditions, which could influence the results.
Dr. Vlad Dionysi, an assistant professor at Carol Davila University, said: "We recommend checking vitamin D levels in adults with depression and correcting any apparent deficiencies as part of general health. At the same time, we need more studies to see if correcting a vitamin deficiency can reduce the risk of depression."
Conduct larger studies with repeated measurements of vitamin D levels.
Measure sun exposure accurately, because the sun helps the body produce the vitamin.
Studying the genes associated with vitamin D to understand the possible causes.
Conducting experiments on people with vitamin D deficiency who do not suffer from depression to see if correcting the deficiency protects against depression.
The study was published in the journal Biomolecules and Biomedicine.
