According to the World Health Organization (WHO), around 5% of adults around the world live with depression.
While there is no available cure for depression, symptoms are often manageable through treatments including psychotherapy and prescription antidepressants.
Prior research has explored the causal relationships between vitamin D, inflammation, and depression. For instance, a 2013 study linked low levels of vitamin D to depression. Another study from 2011 suggested that vitamin D levels may help regulate inflammation, which is linked to depression.
Until now, however, systematic reviews and meta-analyses investigating the link between vitamin D levels and depression have delivered mixed results.
But a new study has systematically reviewed and meta-analyzed randomized controlled trials (RCT) that examined the efficacy of vitamin D supplements in reducing depressive symptoms compared to a placebo.
The researchers found that vitamin D supplementation equal to or exceeding 2,000 individual units (IUs) per day may help reduce depressive symptoms, although they noted their results have “very low certainty.”
The study was recently published in Critical Reviews in Food Science and Nutrition.
The impact of vitamin D supplementation on depressive symptoms
For the study, the researchers examined 41 RCTs including 53, 235 people in their analysis. They looked at data including age, vitamin D levels at baseline and post-treatment, and data on depressive symptoms.
They also included details of vitamin D supplementation, including:
- possible calcium supplementation or add-on medications
Overall, the researchers found that vitamin D supplementation had a small to moderate effect on depressive symptoms.
Effect sizes were slightly larger among people with baseline vitamin D levels below 50 nanomoles per liter (nmol/L) — the borderline for low vitamin D levels — than those with vitamin D levels above this threshold at baseline.
The researchers also noted that while doses up to 2,000 IU daily had a small to moderate effect, those who took over 4,000 IU daily had a larger effect.
What’s more, vitamin D supplementation appeared to have a larger effect when taken for less than 12 weeks compared to longer periods of time.