A person may know he has a vitamin D deficiency if he suffers from muscle weakness and pain in the bones, according to WebMD. He may be especially at risk of the deficiency if he is a strict vegetarian, is dark-skinned and avoids going out into the sun.
The person who needs more vitamin D may also be more susceptible to infection, according to MedicineNet. These infections can affect both the upper and lower respiratory tract but can attack the urinary tract as well. The person may also suffer from depression, especially if he avoids sunlight. He may also suffer from sleep apnea, which causes sleep interruption many times a night. Children with a vitamin D deficiency may suffer from allergies and have an increased risk of dental caries.
Not only may the bones hurt, but they can be misshapen and brittle, according to Mayo Clinic. Other symptoms of vitamin D deficiency are subtle or nonspecific, according to WebMD; however, the lack of the vitamin can put a person at risk for certain cancers, high blood pressure, multiple sclerosis and cognitive problems. Vitamin D deficiency can also increase a person's risk of death from heart disease.
People can obtain vitamin D from animal products, such as fish, milk and eggs. Exposure to the sun's ultraviolet light is another source of vitamin D, according to WebMD.