Suicide is a global health concern ranking among the leading causes of death worldwide. The CDC reports that suicide rates in the U.S. increased by 30% between 2000-2018. Although suicide rates dropped slightly in 2019 and 2020, suicide was still a leading cause of death, with nearly 46,000 people dying by suicide in 2020 alone. Moreover, in the same year, there were many more people seriously thinking about suicide (12.2 million), planning for suicide (3.2 million), or attempting suicide (1.2 million).
While suicide can affect people of all ages and backgrounds, some of the highest suicide rates tend to be among non-Hispanic American Indian/Alaska Native groups, people who identify as non-heterosexual, and military or veteran populations. We are going to focus on the latter for this blog.
Suicide Among U.S. Military Communities
Among the U.S. military and veteran populations, suicide is a critical issue. According to the Department of Veterans Affairs (VA) 2022 National Veteran Suicide Prevention Annual Report, veteran suicide trends mirror non-veteran trends, with suicide rates peaking in 2018 and slightly falling in 2019 and 2020. Yet, although veteran suicide trends matched those of non-veterans, suicide rates did not.
According to the report, in each year from 2001 through 2020, suicide rates of veterans exceeded those of non-veteran U.S. adults by 12.1% to 66.2%. When looking deeper, there appears to be an increased risk of suicide among military and veteran populations in areas with less sun exposure and during the springtime, suggesting that seasonal changes, and possibly vitamin D status, may impact suicide risk.
Vitamin D has been Linked with Depression and Suicide
In addition to the plethora of factors that can lead to depression, U.S. military members may experience stressors such as combat exposure, separation from family, loss of team members, and precarious living conditions that may increase the prevalence of depression in this population. Moreover, due to high physical and physiological demands, inadequate nutrition and rest, and lack of sun exposure due to night operations, protective clothing, or obscure working locations, vitamin D deficiency is widespread among military members.
Both observational and interventional studies have found an association between vitamin D status and depression in both military and non-military populations. A recent systematic review and meta-analysis of observational studies and randomized controlled trials that included over 31,000 participants concluded that vitamin D concentration is associated with depression.
A 2019 study on active-duty service members confirmed these findings and concluded that vitamin D-deficient service members might be at a higher risk for a depression diagnosis.
It is well documented that the greater severity of depression, the greater likelihood of suicidal behavior. So, if vitamin D is associated with depression, is it also associated with suicide?
One case-controlled study examined vitamin D levels in archived serum obtained from active-duty service members who subsequently died by suicide compared to matched controls. Four hundred and ninety-five samples were assessed, and controls were matched by age, sex, and rank.
The researchers found that the risk for suicide was increased in the lowest octile of vitamin D levels, all of which had vitamin D levels below 20 ng/mL when seasonally adjusted. Although the results indicate correlation, not causation, other studies have come to similar conclusions.
For instance, a study of over 157,000 healthy Korean veterans found that vitamin D levels below 10 ng/mL were significantly associated with the risk of suicidal ideation. Another study assessing 215 pediatric patients admitted to the emergency department due to a suicide attempt found that vitamin D levels were significantly lower than a group of controls. The authors concluded that vitamin D deficiency might be one of the causes of suicidal behavior in adolescents.
New Study Finds an Association between Vitamin D supplementation and the Risk of Self-harm and Suicide Among U.S. Veterans
On Feb 1, 2023, a study was published that explored the associations between vitamin D levels, vitamin D3 or D2 supplementation, suicide attempts, and self-harm among U.S. veterans. In this retrospective cohort study, all veterans who received either vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol) prescription refills between 2010 and 2018 were matched 1:1 to untreated veterans.
The veterans were followed and censored at the first instance of a suicide attempt, self-harm, or death, 24 months, or the end of the study period. This was an extensive study, and researchers followed a total of 338,482 veterans in the vitamin D2 group and 981,770 veterans in the vitamin D3 group.
The study found that supplementation with vitamin D2 or D3 is associated with a 45-48% reduced risk of suicide attempts and self-harm, on average, among veterans. Additionally, the researchers found that vitamin D3 demonstrated a dose-response effect in deficient veterans, with more significant reductions in suicide and self-harm risk at higher doses of vitamin D3. Lastly, the associated risk reduction was more significant among Black veterans, who more frequently experience low vitamin D serum levels when compared to their white counterparts.
Potential Mechanisms of Action
The theory that vitamin D may impact suicide risk is of little surprise as evidence of vitamin D’s influence on brain health continues to grow. In fact, vitamin D has been called a “neurosteroid” due to its various effects on the brain.
Several studies have reported that vitamin D can act by differentiating brain cells, regulating axonal growth and calcium signaling in the brain, modulating the production of brain-derived inflammatory compounds and neurotransmitter synthesis, and stimulating the production of neurotrophic factors and the expression of genes/proteins involved in neuronal structure. When considering mechanisms of action specific to depression and suicide risk, two seem to stand out in the research above the rest.
First, vitamin D can influence neurotransmitters and neurotrophic factors in the brain, such as BDNF (brain-derived neurotrophic factor) and dopamine. BDNF is a nerve growth factor that facilitates neuronal survival, plays roles in neuronal development, morphology, and synaptic function in the brain, and has been associated with learning, memory, and depression. Vitamin D levels are inversely related to both BDNF and depression levels. Moreover, vitamin D supplementation has been found to significantly mitigate age-related drops in BDNF levels compared to control groups.
Evidence has found that dopamine may play a role in depression and an individual’s ability to cope with suicidality as well. Dopamine is a neurotransmitter known to play a role in motivational and emotional processing. Evidence has found that an imbalance in its action is associated with suicide. Rodent models have concluded that vitamin D is directly involved in regulating the expression of dopaminergic-associated genes. Although evidence is limited, studies have also found vitamin D supplementation to increase serum dopamine levels in child participants.
Finally, vitamin D can influence pro-inflammatory cytokines. Scientists have theorized that increased inflammation might play a role in the pathophysiology of depression and suicide. Therefore, suicidal patients might be experiencing both low vitamin D status and high levels of inflammatory cytokines.
This theory has been tested several times. A study published in 2011 was the first to report increased levels of pro-inflammatory cytokine concentrations in suicide attempters compared to non-suicidal depressed patients and healthy controls. Studies since then have observed that suicide attempters have significantly lower mean vitamin D levels than depressed non-suicidal patients and healthy controls and that there is a significant negative association between vitamin D and pro-inflammatory cytokine levels in the patients tested.
Vitamin D is a crucial nutrient/hormone that plays a role in several aspects of health and well-being. Although vitamin D can be found in food sources, it’s estimated that the effect of sunlight produces 90% of our vitamin D levels. Depending on sunlight for vitamin D has proven to be insufficient due to varying levels of sun exposure depending on the time of year and latitude of locality, variations of sun protection from clothing to sunscreen, as well as the physiological differences in vitamin D metabolism that comes with age and variations in skin color.
According to recent evidence, oral vitamin D is associated with a 45-48% reduction in the risk of suicide attempts and intentional self-harm among veterans. According to the report, vitamin D3 is the optimal form for mental health benefits. Vitamin D’s function in the production of neurotransmitters and neurotrophic factors, as well as its ability to reduce inflammation might explain its role in suicide risk reduction.
Vitamin D deficiency and insufficiency are prevalent among U.S. military Service Members and general populations. Vitamin D status may be a useful screening tool to identify service members, and other citizens, at risk for depression, self-harm, and suicide. Restoring and maintaining adequate vitamin D levels may represent a safe and valuable strategy for mitigating mental health risks and promoting healthy brain aging.
If you or someone you know is in crisis, please get in touch with the 988 Suicide and Crisis Lifeline. Call or text 988, or chat at 988lifeline.org. 988 is confidential, free, and available 24/7/365.