As autumn arrives and daylight retreats, the human body quietly begins to lose something essential — vitamin D, the nutrient synthesized from sunlight that underpins bone strength, energy, immunity, and mood. Physician Dr. Kunal Sood has outlined five symptoms that signal this depletion: bone pain, fatigue, muscle weakness, mood changes, and increased vulnerability to illness. The seasonal pattern is ancient and physiological, affecting millions in temperate climates, yet the deficiency it produces is among the most preventable of modern health concerns. Awareness, timed to the turning of the