Reply to M van Lieshout and S de Pee

Program in International Nutrition and
Department of Nutrition
University of California, Davis
One Shields Avenue
Davis, CA 95616
E-mail: mjhaskell{at}ucdavis.edu

Dear Sir:

 We reported estimates of the relative vitamin A equivalency of ß-carotene in oil, sweet potatoes, and Indian spinach with use of the paired deuterated-retinol-dilution (DRD) technique (1). This technique measures the change in the total-body vitamin A pool size after a period of consumption of a controlled diet with a consistent source of vitamin A. The DRD technique has been validated against liver vitamin A concentrations in surgical patients with low to adequate vitamin A stores (2, 3), and it has been shown that the DRD technique detects quantitative changes in the vitamin A pool size that are similar to the expected changes after prolonged (75 d) consumption of known amounts of retinyl palmitate (4). In our recently published study, the total-body vitamin A pool size was estimated in Bangladeshi men before and after 60 d of supplementation with 750 µg retinol equivalents (RE)/d as either retinyl palmitate, ß-carotene, sweet potato, or Indian spinach, or with 0 µg RE/d, in addition to a low–vitamin A diet (200 µg RE/d). Mean changes in the vitamin A pool size in the groups that received a ß-carotene source were compared with the mean change in the pool size of the retinyl palmitate group to estimate the relative equivalency of these vitamin A sources. van Lieshout and de Pee reported estimates of vitamin A equivalency for ß-carotene in oil (5) and dark-green leafy vegetables (DGLV) (6) that differ from our estimates. We address the issues they raised regarding these discrepancies below.

We estimated a vitamin A equivalency factor of 6:1 for ß-carotene in oil, whereas van Lieshout et al (5, 7) estimated factors of 2.4:1 to 3.2:1 by using the plateau isotope enrichment (PIE) technique. van Lieshout and de Pee suggest that the amount of oil in the ß-carotene capsule in our study was insufficient to solubilize the ß-carotene. The capsules were prepared by using food grade microcrystalline ß-carotene suspended in corn oil (30% FS; Roche Vitamins, Parsippany, NJ), which was further diluted in corn oil to 11.3 mg/mL (confirmed spectroscopically at 450 nm). Thus, we do not believe this explains the discrepant results.

We estimated a vitamin A equivalency factor of 10:1 for ß-carotene in Indian spinach, whereas de Pee et al (6) estimated a factor of 26:1 for DGLV on the basis of changes in serum retinol concentrations. van Lieshout and de Pee suggest that possible reasons for this discrepancy are that the Bangladeshi men in our study had adequate vitamin A status and were dewormed, whereas the Indonesian children and Vietnamese women in their studies had low vitamin A status and were not dewormed. In our study, Bangladeshi men with the lowest serum retinol (0.52–1.25 µmol/L) and normal C-reactive protein (<5 mg/L) concentrations were selected. Their mean serum retinol at baseline was 0.94 ± 0.21 µmol/L, and their mean initial vitamin A pool size was 0.108 ± 0.067 mmol (0.091 µmol/g liver), which indicates marginal vitamin A status. The vitamin A status of the Indonesian children (6) was based on serum retinol concentration only, which can be affected by the acute phase response and iron status (8, 9). Markers of subclinical infection were not assessed, and children were selected on the basis of low hemoglobin or hematocrit and had low initial serum ferritin concentrations. Thus, it is difficult to interpret the serum retinol concentrations or to draw any conclusions about the children's vitamin A status. Moreover, van Lieshout and de Pee state that the vitamin A equivalency factors determined by use of PIE for both healthy Dutch adults (7) and Indonesian children with marginal vitamin A status (5) were similar, which suggests that vitamin A status has no effect on bioefficacy. It is possible that intestinal parasites reduce the absorption of ß-carotene. However, van Lieshout et al (5) suggested that the low prevalence and intensity of intestinal parasites in the Indonesian children had a negligible effect on the bioefficacy of ß-carotene in oil.

van Lieshout and de Pee suggest that the food preparation methods used in our study enhanced the bioavailability of ß-carotene from the foods. The studies by de Pee et al (6, 10) suggested that consumption of plant sources of vitamin A has little or no effect on vitamin A status when vegetables are stir-fried and subjects are not dewormed. In our study, we chose to use optimal food preparation techniques and to deworm our subjects to determine whether plants sources of vitamin A are efficacious for improving vitamin A status under these conditions. Having observed a positive effect under optimal conditions, we are planning to quantify the effect of various food preparation methods on bioefficacy. It is likely that estimates of vitamin A equivalency for any given food will vary greatly depending on food preparation methods. It is conceivable that daily consumption of mashed or puréed fruit or vegetables could have a positive effect on the vitamin A status of children, and these are not uncommon food preparation techniques for this age group.

van Lieshout and de Pee suggest that the PIE technique is more precise than is the paired DRD technique and requires less time to estimate vitamin A equivalency factors (21–42 d versus 113 d, respectively). Using the paired DRD technique, we were able to detect significant differences by treatment group with 14 subjects per group. Although the PIE technique requires less time, it provides an estimate of relative vitamin A equivalency only, whereas the paired DRD technique provides both an estimate of quantitative changes in the vitamin A pool size in response to an intervention (efficacy) and estimates of relative vitamin A equivalency.

The choice of method for estimating vitamin A equivalency factors will differ depending on the research question, the population studied, available instrumentation, and cost. We think it is desirable to study the same question with different methods to cross-validate results. Moreover, it is important to quantify the effect of food preparation methods and other factors on the bioavailability of ß-carotene to develop interventions to improve the bioefficacy of ß-carotene from foods that are available to populations at risk of deficiency.

ACKNOWLEDGMENTS

The authors had no conflict of interest to report.

REFERENCES

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