Vitamin D supplements can help reduce airway remodeling in rats with asthma by lowering the expression of a protein called TGF-β1. In the study, rats with asthma were given different doses of vitamin D, and those receiving higher doses showed less airway remodeling and inflammation. The levels of TGF-β1 were lower in rats treated with vitamin D compared to those without treatment. This suggests that vitamin D may have a protective effect against airway remodeling in asthma by decreasing TGF-β1 expression.