Bone pain and muscle fatigue are symptoms of a vitamin D deficiency, according to WebMD. A basic blood test performed by a doctor can reveal low levels of vitamin D. However, a mild deficiency may exhibit no signs at all, explains MedicineNet.
Low vitamin D levels also contribute to the presence of asthma, cognitive impairment and cancer. Those who have had gastric bypass surgeries or have cystic fibrosis or diseases of the liver have increased difficulty of retaining vitamin D, and levels tend to be naturally low without added supplements, according to MedicineNet. An efficient amount of vitamin D can aid in the treatment of diabetes, high blood pressure and multiple sclerosis.