It's a good idea to call your doctor and ask for a Vitamin D blood level test.
Vitamin D is one of the few supplements that we *really* do need, most everyone is deficient, especially during the winter months. If you have any ailment, it most likely can be improved by maintaining an optimum vitamin D level. From the Vitamin D Council they state that
"Vitamin D targets over 2000 genes (about 10% of the human genome) in the human body. Current research has implicated vitamin D deficiency as a major factor in the pathology of at least 17 varieties of cancer as well as heart disease, stroke, hypertension, autoimmune diseases, diabetes, depression, chronic pain, osteoarthritis, osteoporosis, muscle weakness, muscle wasting, birth defects, periodontal disease, and more."
On a blood test, this level would read between 50–80 ng/mL. Anything from a chronic cough to the winter blues to improving bone density, can be improved by taking a vitamin D3 supplement, eating more foods with natural vitamin D (fish, whole eggs from pastured chickens and cod liver oil), and getting more sunlight on your skin.
If you ever have any health related questions for me, or just need a second opinion, don't hesitate to ask me! I also offer nutrition consultations if you want to go more in depth.