Please explain what it means when u have low vitamin d?

Vitamin D: Low vitamin d it is below about 20. Research shows that raising your vitamin d level can boost immunity, elevate mood, and more. The darker your skin, the lower vitamin d can be because we make it through the sun on our skin. About 60% of whites in us are low, about 75% latino low, and maybe 85-90% african americans low. Experts say between 50-80 is optimal. 20s or 30s is minimal.