I have posted studies here before that finds low D levels associated to depression, but this is very encouraging. Suicide rates have been climbing, especially in veterans. These are very impressive numbers and the study performed by the Veterans Affairs with US vets no less:

"Overall, vitamin D3 use was linked to a 45% lower risk of suicide attempts and self-harm, and vitamin D2 was linked to a 48% lower risk.

Among the vitamin D3 group, 1,786 veterans (0.36%) not on supplements had a suicide attempt or instance of intentional self-harm, compared with 991 veterans (0.2%) with supplementation. Similarly, among the vitamin D2 group, 878 veterans (0.52%) without supplements had a suicide attempt or intentional self-harm, compared to 452 veterans (0.27%) with supplementation."

https://www.webmd.com/vitamins-and-s...icide-attempts

Study:

The association between vitamin D serum levels, supplementation, and suicide attempts and intentional self-harm