What is the connection between vitamin d deficiency and leukopenia?

None: Vitamin d deficiency is not a common cause of leukopenia. Here in spokane wa you don't even have to check vitamin d to document deficiency, as it is universal, but not all who are deficient are leukopenic.

Immune system: Low vitamin d affects immune function which may affect levels of white blood cells. A 2008 study showed that supplementing d improved WBC production of canthelicidin, a peptide which kills bacteria. Take at least 5000 iu daily and have your level checked at 3 months - it should be above 50. I keep mine at about 80 (normal 30-100) and take my probiotic daily to keep my gut immune system healthy.