a negative trendp < 0.001
The only significant linear trend was a negative trend between serum folic acid levels and participants’ age (R 2 = 26.32%, β = −0.55 ± 0.11, p < 0.001), as well as a negative trend between serum folic acid levels and IgE levels (R 2 = 2.91%, β = −35.72 ± 30.36, p = 0.021).