Everyone should have his or her vitamin D level checked at least once a year, preferably twice. There is wide-spread debate in the medical community about optimal vitamin D levels, and as with most nutrients, the answer likely varies for each unique person given their genetics, environment, lifestyle, and existing health challenges. However, clinical research is starting to uncover that significantly elevated vitamin D might have as much negative consequences as too little.
Generally, individuals need to maintain their vitamin D in the 40-60 ng/ml range. Lower levels are associated with a variety of immune deficiencies. However, higher levels can be immunosuppressive; This may be useful short term in the case of autoimmune or other aggressive, inflammatory disease. However, if there is an infectious component of the disease root causes, then vitamin D will likely need to come down eventually to more moderate levels in order to allow optimal immune functioning to eradicate root causes.