Some persons may experience fatigue, body soreness, muscular weakness, joint discomfort, low energy, or bone weakening when their vitamin D level is below normal, at 18 ng/mL. Regular morning sun exposure, a nutritious diet, exercise, and foods fortified with vitamin D can occasionally help with mild deficiencies, but many people also require supplements like Vitamin D3 for greater recuperation. It is best to talk to your doctor about supplementation because the right dosage depends on your age, symptoms, calcium levels, and general health.