Original article published in Psychiatric Times.

Revisiting Vitamin D in Psychiatry

Of the many researched integrative medicine interventions for the treatment of mental health conditions, perhaps one of the simplest is vitamin D. While controversy around its use remains, including recent guidelines that recommend against testing vitamin D levels for virtually any reason,¹ my own clinical experience combined with the latest research strongly suggest benefits for a number of mental health conditions.

Long recognized for its role in calcium metabolism and bone health, more recent research has been highlighting other important functional aspects of vitamin D. Better described as a steroid prohormone than a vitamin, vitamin D plays a prominent role as a neuroprotective agent, reducing neuroinflammation, supporting serotonin synthesis, and improving brain plasticity.² These effects are likely why the vitamin is relevant for mental health, with a growing body of research demonstrating vitamin D deficiency may have clinical implications for depression, suicide prevention, attention-deficit/hyperactivity disorder (ADHD), and anxiety treatment.

From Bone Health to Brain Health

Vitamin D was initially discovered as the cure for preventing rickets.³ Cod liver oil, rich in both vitamin A and vitamin D, was found to be effective for treating the condition. Since cod liver oil was known to be high in vitamin A, it was assumed that vitamin A was needed for the deposition of calcium in bone. However, careful experiments that removed vitamin A from cod liver oil found that it still prevented rickets, suggesting the presence of a separate nutrient which later became known as vitamin D.

Long considered just a vitamin important for calcium absorption and bone health, research near the end of the last century started to find vitamin D receptors throughout most tissues of the body, including the brain.⁴ The receptor was found to influence genetic expression with effects on immune function.⁵ More recently, it has been shown that vitamin D regulates neurotransmitter levels, including serotonin (Figure 1), through a number of different mechanisms.⁶

Figure 1. Vitamin D and Serotonin Synthesis

Based on this broader understanding of the effects of vitamin D, numerous studies have documented the effects of vitamin D deficiency on mental health.

A Model for Prevention and Treatment: Clinical Implications of Vitamin D

Vitamin D and Depression

The most well-documented effects of vitamin D on mental health is with depression. Initially, low vitamin D was hypothesized to be a cause of seasonal affective disorder (SAD) due to the fact that vitamin D levels are lower in the winter. Initial clinical trials showed benefits on mood in healthy subjects and those with SAD over the winter months.^{7, 8} While not all studies were positive,⁹ based on the results, research started exploring benefits in other types of depressed patients. A larger study in overweight individuals with depression found significant benefits with vitamin D,¹⁰ as did a separate trial using vitamin D as an adjunct treatment for depression when combined with standard medication.¹¹

Unfortunately, a lot of the research on vitamin D suffers from poor methodology. Many studies did not test patients’ vitamin D status or they provide the same dose of vitamin D regardless of an individual’s vitamin D levels; individuals deficient in vitamin D will clearly have a better response. Other studies have used lower doses that likely minimize the clinical benefits. Even with these limitations, the latest meta-analyses have found that low vitamin D levels correlate with depression and that treatment with vitamin D provides significant improvements in depressive symptoms.^{12, 13}

Vitamin D: A Lifeline in Suicide Prevention

The rising rates of suicide in the United States continues to be of major concern. While there are numerous calls for increasing awareness and screening, there is little discussion about direct treatment, especially of underlying biochemical risk factors. And one of the more common risk factors for suicide is vitamin D deficiency.

Low vitamin D levels have been found to correlate with suicide risk. A study in 2013 found that low vitamin D was common in active military service members. They also found that the lowest levels were correlated with suicide risk.¹⁴ A study of depressed patient who attempted suicide found lower levels of vitamin D and higher levels of inflammation in the blood as compared to depressed patients who did not attempt suicide.¹⁵

A meta-analysis in 2023 found that low vitamin D was associated with suicidal behaviors.¹⁶ A retrospective study on over 300,000 veterans found that vitamin D supplementation almost halved the risk of suicide. Those who were dark skinned or deficient in vitamin D had their suicide risk reduced by 64%.¹⁷

Vitamin D levels are easy to check and treat when found to be low. Considering the challenges around suicide prevention, adding vitamin D supplements for those who are deficient is a simple approach that could save lives.

Nourishing Young Minds: The Role of Vitamin D in ADHD

As a nutrient, vitamin D appears to be critical for normal brain development in childhood. A systematic review on vitamin D supplementation and mental health in children noted positive influences of the vitamin on numerous aspects of mental health.¹⁸ Vitamin D supplementation is recommended for mother’s who are deficient during pregnancy as it appears to be protective against the development of ADHD and autism.¹⁹

A meta-analysis from 2019 found that vitamin D levels are significantly lower in children with ADHD.²⁰ That same year a separate meta-analysis looked at the effects of vitamin D supplementation on ADHD symptoms. They found that when used as an adjunctive therapy, vitamin D decreased ADHD symptoms and improved vitamin D status.²¹ It was also noted that vitamin D supplementation was devoid of serious side effects.

Vitamin D: Potential to Alleviate Anxiety

Vitamin D may also have benefits for reducing anxiety symptoms. A small study in patients with generalized anxiety disorder and vitamin D deficiency compared standard treatment to standard treatment plus vitamin D. For the patients treated with vitamin D, anxiety levels decreased by almost one-third as compared to no significant change in the group that received standard care alone.²²

A study in women with prediabetes and low vitamin D levels also showed improvements in anxiety with vitamin D supplementation, both with and without the addition of fish oil.²³ With vitamin D alone, anxiety levels decreased 19%. When combined with fish oil, levels were reduced by 30%. A separate study in adolescents with premenstrual syndrome and severe vitamin D deficiency, vitamin D supplementation reduced anxiety scores by 61% as compared to no appreciable change with placebo.²⁴

While these results are promising, it is worth noting that not all studies have found benefits. A study using vitamin D for depression prevention in individuals aged 60 to 80 years old did not find significant benefits for anxiety symptoms.²⁵ An earlier trial exploring the effects of vitamin D in patients with lower levels did not find significant changes in depression or anxiety symptoms.²⁶ However, in the study, depression and anxiety symptoms were quite low at baseline, as the only criterion used for selecting patients was just having a low vitamin D level. Arguably, the clinical trial may have found better results if they had treated symptomatic patients with low vitamin D levels versus those without significant mental health symptoms.

My own clinical experience has highlighted the importance of testing vitamin D levels in any patient struggling with a mental health diagnosis. In deficient patients, vitamin D supplementation is often helpful in reducing symptoms and improving overall wellbeing.

An Essential Yet Overlooked Laboratory Test in Psychiatry

Vitamin D deficiencies are common in patients with mental health diagnoses. The research has found benefits with vitamin D supplementation for depression, anxiety, suicide prevention, and ADHD. Research into levels of vitamin D in patients with obsessive-compulsive disorder have also found their levels to be low.^{27, 28} And a study on subjects with post-traumatic stress disorder (PTSD) found lower levels of the vitamin.²⁹ Interestingly, the researchers also noted genetic polymorphisms of vitamin-D binding protein that correlated with lower vitamin D status in patients with PTSD. Unfortunately, guidelines around vitamin D testing and supplementation continue to ignore most of the data suggesting benefits beyond bone health.

I have found vitamin D deficiency to be a key component that is often ignored by psychiatry. The simplest approach to identify patients who need supplementation is through testing. In patients who are severely deficient, higher doses may be necessary to achieve optimum levels. Testing is also critical to monitor vitamin D levels of some patients who have poor absorption of vitamin D supplements.

The core principle of integrative medicine is biochemical individuality: recognizing that all patients are different and have different genetic variability and environmental stressors. Vitamin D testing and treatment can be one simple step towards incorporating personalized medicine into psychiatry.

While vitamin D should not be seen as a silver-bullet cure-all for mental health problems, it is a fundamental nutrient that is vital for the normal function of brain neurochemistry. It is also commonly deficient. Supporting vitamin D is foundational for developing a personalized approach to mental health care, and for supporting the efficacy of other treatments. Considering how many patients with mental health conditions struggle with residual symptoms even with standard treatment, simple interventions, like vitamin D, could have a profound impact on the health of our patients.