Interventions
A survey demonstrated that Japanese women in their 20s consume 6.2 ± 2.5 mg (mean ± SD) of iron daily (Ministry of Health, Labour, and Welfare, 2019. National Health and Nutrition Survey Report). Thus, iron dosages were determined to be 6 mg/day to meet the Japanese iron Dietary Reference Intake (DRIs, 10.5 mg/day). Here, the first group was instructed to take two capsules containing 200 mg of methionine, 400 mg of threonine, and 6 mg of iron (57.7 mg of sodium ferrous citrate) with a cup of water once daily, 2 h after meals (FEMT group). The second group was instructed to take the same number of capsules containing 6 mg of iron simultaneously and in the same manner (FE group). The third group was instructed to consume a composition containing no amino acids or iron (PCG group). Methionine and threonine were supplied from Ajinomoto Co., Inc., and sodium ferrous citrate was supplied from Mitsubishi chemical co., ltd. All participants were asked to record their daily consumption. The duration of the intervention period was set at 6 weeks.