From the Karolinska Institute in Stockholm, Sweden comes the first of what I hope will be many studies on how vitamin D affects the prescription drugs people take. Dr. Jonatan Lindh and his colleagues found that some commonly prescribed immunosuppressants have seasonal variations in their blood levels and that seasonality is directly related to vitamin D levels. It turns out that vitamin D increases levels of a key enzyme made by the liver (CYP3A4) and increased levels of CYP3A4 means that blood concentrations of certain prescription drugs will be lower.

Theoretically those drugs include a long list, including the SSRIs citalopram, escitalopram, fluoxetine, norfluoxetine and sertraline, and the antipsychotics aripiprazole, haloperidol, risperidone and ziprasidone. I only mention those because I am a psychiatrist. For a full list of drugs that may have lower blood levels because of vitamin D increasing CYP3A4, look up CYP3A4 in Wikipedia and read about the enzyme. Again, vitamin D increases the liver’s production of this vital enzyme, an enzyme which then lowers levels of the drugs it catabolizes (breaks down).

Lindh JD, Andersson ML, Eliasson E, Bjorkhem-Bergman L. Seasonal variation in blood drug concentrations and a potential relationship to vitamin D. Drug Metab Dispos. 2011 Feb 24. [Epub ahead of print] http://www.ncbi.nlm.nih.gov/pubmed/21349923