Blot 1980.

Methods	Type of study: parallel, 2‐arm randomised controlled trial Country of study: France Study setting: single transfusion centre Number of participants randomised: Treatment arm 1: 91 Treatment arm 2: 80 Number of participants analysed: Treatment arm 1: 73 (42 male, 31 female) Treatment arm 2: 70 (43 male, 27 female) Follow‐up time points: first donation after baseline donation Hb threshold for deferral from donation: not reported Source of funding: not reported
Participants	Regular donors (at least 1 prior donation) Mean age (years): combined treatment arms: 36.4 (SD 9.5, range 20 to 59) (male); 34.1 (SD 10.8, range 18 to 56) (female) Sex (male/female): 57.3%/62.7%
Interventions	Treatment arm 1: oral iron and ascorbic acid (Fero‐Grad Abbott); 105 mg iron and 500 mg ascorbic acid taken daily in the morning Total dose: 3150 mg per month Treatment arm 2: control (no iron supplementation or placebo)
Outcomes	Haemoglobin; MCV; total serum iron; total iron binding capacity; serum ferritin
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	The method of randomisation was not reported
Allocation concealment (selection bias)	Unclear risk	Allocation concealment was not reported
Blinding of participants and personnel (performance bias) All outcomes	High risk	Study participants were not blinded
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Blinding of outcome assessors was not reported
Incomplete outcome data (attrition bias) All outcomes	High risk	The number of withdrawals differed between treatment arms (18/91 versus 10/80) and 10.5% of randomised participants were lost to follow‐up
Selective reporting (reporting bias)	Unclear risk	All outcomes listed in the manuscript were reported, but no study protocol was available to determine the full list of pre‐specified outcomes
Other bias	Low risk	No other sources of bias identified