PPIB and Hepatitis: The 8% difference in hepatitis B vaccination response between people who were vitamin D sufficient and 25(OH)D < 50 nmol/L, and the 18% difference between winter and summer (Figs. 3a, 4d) are comparable with the effects on the hepatitis B vaccine response shown for other lifestyle factors, e.g., smoking, obesity and poor sleep [13, 15].