C4A and systemic lupus erythematosus: Compared with the vitamin D sufficiency group (C3 0.48 ± .022 g/L, C4 0.07 ± 0.05 g/L), children with lupus in the vitamin D-insufficiency group had lower levels of C3 and C4 (C3 0.35 ± 0.21 g/L, C4 0.06 ± 0.05 g/L) (P < 0.05).