Fig. 1

Study design and vitamin C levels at baseline and after patients had been randomized to 500 mg vitamin C or placebo. a Study design. Days 1, 5, and 28: before vitamin C/placebo exposure. Day 32: after short-term vitamin C/placebo exposure. Days 56, 60, and 84: after longer-term vitamin C/placebo exposure. b Plasma vitamin C status at baseline. Normal + suppl.: patients who had been taking vitamin C/multivitamin supplement at the time of inclusion. c Plasma vitamin C concentration at baseline and after randomization to vitamin C (500 mg) or placebo. Red line represents the threshold for severe vitamin C deficiency (11.4 μM) [16]. Black line represents the threshold for vitamin C deficiency (23 μM). Patients who had been taking vitamin C supplements at the time of study inclusion are marked using green circles. Time-periods of daily intake of vitamin C or placebo are highlighted using green boxes. Dotted lines indicate timepoints with missing plasma vitamin C levels. Data presented as spline mean (blue line) with standard error ribbons for cycles; C cycle, D day in cycle.