TABLE 2.
RID-predicted TBS and estimated liver vitamin A concentrations in healthy young people and in subjects with SCD-HbSS before and after vitamin A supplementation1
| Group | TBS (μmol) | P value | Liver VA concentration (μmol/g) | P value |
|---|---|---|---|---|
| SCD-HbSS (n = 22) | 389 (162–1288) | 0.813 | 0.302 (0.0992–1.04) | 0.663 |
| Healthy (n = 20) | 406 (182–1038) | 0.277 (0.113–1.00) | ||
| SCD-HbSS paired comparisons | ||||
| 3.15 or 6.29 μmol retinol/d | ||||
| Before (n = 20) | 412 (162–1288) | 0.985 | 0.335 (0.112–1.04) | 0.841 |
| After (n = 20) | 415 (155–965) | 0.327 (0.104–0.826) | ||
| 3.15 μmol retinol/d | ||||
| Before (n = 9) | 540 (162–1288) | 0.0892 | 0.428 (0.112–1.04) | 0.838 |
| After (n = 9) | 435 (165–965) | 0.336 (0.113–0.826) | ||
| 6.29 μmol retinol/d | ||||
| Before (n = 11) | 323 (195–554) | 0.112 | 0.269 (0.144–0.544) | 0.178 |
| After (n = 11) | 381 (155–730) | 0.314 (0.104–0.648) | ||
RID, retinol isotope dilution; SAp, plasma retinol specific activity; SCD-HbSS, sickle cell disease hemoglobin SS type; TBS, vitamin A total body stores; VA, vitamin A.
Values are geometric mean (range) for TBS and liver vitamin A concentration for young people with SCD-HbSS before and after 8 wk of vitamin A supplementation (either 3.15 or 6.29 μmol/d) as well as for healthy subjects of similar age. For all subjects, TBS were calculated by RID Equation 1 (see Methods) using group values for the composite coefficient FaS derived from modeling the pre-supplementation super-subject dataset for the SCD-HbSS subjects along with each subject’s SAp at the corresponding time. For 19 of the 20 healthy individuals, TBS were calculated at 3 d after isotope dosing and for 1 subject at 5 d. For the subjects with SCD-HbSS before supplementation, TBS for all 22 participants were calculated at 3 d postdosing whereas after supplementation, TBS were calculated for 14 of the subjects with SCD-HbSS at 3 d, for 4 subjects at 4 d, 1 at 7 d, and 1 at 8 d. The following values for FaS were used for RID predictions: 2.40 at 3 d, 1.67 at 4 d, 1.34 at 5 d, 1.06 at 7 d, and 0.989 at 8 d. Liver VA concentration was estimated as TBS (μmol) × fraction of TBS stored in the liver / estimated liver weight (g), assuming that 80% of TBS are stored in the liver [40] and calculating liver weight using the regression equation presented in [41]. Predictions of TBS and liver VA concentration were compared by the specified groupings using a paired t test, Wilcoxon test, or Mann-Whitney test; results showed that there were no significant differences.