It is known that there is a link between low vitamin D status and increased risk of developing autoimmune disorders. I think what the ACS is trying to say is that the vitamin D helps regulate the immune system so that it is less likely to jump into the autoimmune direction.
I have also read that macrophages (immune cells that engulf and digest bacteria, etc.) are more effective at doing their job when there is adequate vitamin D in the body.
I hope this helps - take care,
Chronic Lyme Disease, Chronic Bartonella (clinical dx only), Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, chronic Lymphopenia, etc.; G-Tube; Currently trying to wean off TPN.
Meds: Pulmicort, IV Ceftazidime, Heparin (to flush PICC line), Claritin, Domperidone, Colloidal Silver (used topically), probiotics, Milk Thistle, Ailanthus, homeopathy.