Incidence of individual symptoms in the iron and placebo groups. A, percentage of participants in each group reporting nausea, heartburn, abdominal pain (ABD pain), constipation, change in bowel movements (Bowel mov) or the presence of black stool movements on at least one day of each week of the intervention or wash-out periods (i.e. data from boxes ‘C’ and ‘H’ on the questionnaire (Figure 1)). The number of participants reporting symptoms in the iron group was significantly higher than that of the placebo group (p = 0.01). B, mean number of black bowel movements per day, obtained from box ‘H’ of the questionnaire (Figure 1), in the iron group (no black bowel movements were reported in the placebo group). Error bars represent standard error of mean (SEM). *p < 0.05; **p < 0.01 for comparison between each treatment day and the baseline (i.e. day 0). ##
p < 0.01 for comparison between each wash-out day and the end of the treatment period (i.e. day 7).