Participants. Nonpregnant, nonlactating women (18–45 y of age) were recruited from Mirpur, a low-income area of Dhaka City in Bangladesh. Potential study participants were examined by a physician to assess their current health and pregnancy status and to obtain information on their medical and reproductive histories. A urine sample was obtained to test for pregnancy. A small blood sample (5 mL) was obtained for measurement of the hemoglobin concentration and serum concentrations of C-reactive protein (CRP) and retinol. Women were considered eligible for the study if they were nonpregnant; free of chronic disease, signs and symptoms of VA deficiency, and severe anemia (hemoglobin <90 g /L); and had plasma retinol concentrations >0.70 mmol/L and #1.05 mmol/L and normal plasma concentrations of CRP (<5 mg/L). We selected women with low, but not deficient, VA status because the activity of the intestinal enzyme b, b-carotene 15,15’-monooxygenase 1 (BCM01), which converts b-carotene to VA, is regulated by VA status and women with low status are more likely to convert dietary b-carotene to VA (4). Also, in our previous studies in Bangladeshi men who were selected using the same criteria for plasma concentrations of retinol and CRP, VA pool size increased in response to supplementation with a small daily amount of dietary b-carotene for 60 d (375 RAE/d). Thus, we selected women who were likely to respond to the planned intervention with OFSP. Written, informed consent was obtained from each participant prior to conducting any of the study procedures. The study protocol was approved by the Institutional Review Board of the University of California, Davis, and the Ethical Review and Research Review Committees of the International Centre for Diarrheal Disease Research, Bangladesh (ICDDR,B).
Study design. The study was conducted as a randomized controlled trial. Women were randomly assigned to 1 of the following 4 groups to receive the following for 6 d/wk over 10 wk: 1) 0 mg retinol activity equivalents (RAE) as boiled white-fleshed sweet potatoes (WFSP) and a capsule containing 150 mL corn oil (WFSP group), 2) 600 mg RAE as boiled OFSP and a capsule containing 150 mL corn oil (B-OFSP group), 3) 0 mg RAE as boiled WFSP and a capsule containing 600 mg RAE as retinyl palmitate in 150 mL corn oil (VA group), or 4) 600 mg RAE as boiled and fried OFSP and a capsule containing 150 mL corn oil (F-OFSP group). A daily intake of 600 mg RAE provides 120% of the FAO/WHOrecommended safe intake for women of reproductive age.
Study procedures. The participants were treated for intestinal helminths (500 mg albendazole) 1 wk prior to beginning the study procedures. During their initial visit to the study facility, the women were weighed, measured, and interviewed to obtain information on their dietary VA intake and morbidity during the previous week. Thereafter, the women received an oral dose of 0.028 mmol retinol equivalents (RE) of [2 H4]-retinyl acetate, and a blood sample (10 mL) was obtained after an overnight fast 20 d later for measurement of the plasma isotopic ratio of [2 H4]-retinol:retinol and estimation of their initial total body VA pool size. Plasma concentrations of retinol, carotenoids, and CRP were measured at the same time point, and dark adaptation was assessed by using the pupillary threshold test. During the initial 20-d mixing period (study days 0–20), the women consumed their usual diets. On d 21 of the study, the women began receiving their assigned dietary and capsule supplements, 6 d/wk, for 10 wk. Immediately after the 10-wk intervention period, a blood sample (10 mL) was obtained after an overnight fast for measurement of the plasma concentrations of retinol, carotenoids, and CRP, and the dark-adaptation testing was repeated. Thereafter, women resumed their usual diets. Ten days later, a blood sample (10 mL) was obtained after an overnight fast for measurement of plasma isotopic ratio of [2 H4]-retinol:retinol. (The plasma isotopic ratio is measured after the 10-d stabilization period as a baseline measurement prior to administering the second dose of stable isotope–labeled VA for estimation of final VA pool size.) Immediately after obtaining the blood sample, women received a second oral dose of 0.028 mmol RE of [2 H4]-retinyl acetate, and blood (10 mL) was obtained after an overnight fast 20 d later for measurement of the plasma isotopic ratio of [2 H4]-retinol: retinol and estimation of the womens final total body VA pool size. Throughout the study period, an FFQ was administered to women weekly to obtain information on their consumption of VA-containing foods during the previous week, and a morbidity questionnaire was administered to the women weekly to obtain information on symptoms of selected illnesses during the previous week.