Int Immunopharmacol (2021) 99:107970
Kidney or liver problems : Severe kidney or liver impairment may affect how these medications are processed in your body
Holmes, high-dose berberine "acts on similar glucose pathways and may compound effects, increasing the risk of hypoglycemia." Berberine lowers blood sugar the same way some diabetes drugs do, so taking both together could drop your blood sugar dangerously low
The above is usually talked of in terms of 'anaemia', but it does show that there is a complicated link between B12, B6, folic acid, zinc and vitamin D levels, chronic disease (anaemia of chronic disease) and how the body 'manages' serum iron, ferritin, and transferrin iron saturation and keeps these in balance (or not, as in your case)
Purpose: Tone equalization, Brightening, Pore tightening, Against imperfections, Moisturizing, Restoring
Proceedings of the Nutrition Society, 2000