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Reply to EH Harrison and JC Smith

Helen Keller International Jl. Patra Kuningan XIV, No 12 Jakarta 12950 Indonesia E-mail: sdepee{at}compuserve.com

Dear Sir:

The remark by Harrison and Smith that there was no significant difference in serum retinol response between the vegetable and fruit groups is correct. However, analysis of duplicate portions showed that the vegetable group had received more provitamin A than the fruit group [684 compared with 535 retinol equivalents (RE)/d]. When corrected for this difference of intake, the difference in the change in serum retinol concentration between the fruit group and the vegetable group was 0.064 µmol/L, which is similar to the difference found between the vegetable group and the control group (0.07 µmol/L).

Accounting for the difference in the amount of carotenoids provided, we derived the following retinol conversion factors (µg ß-carotene equivalent to 1 RE) for fruit and for leafy vegetables and carrots: 12 (95% CI: 6, 29) and 26 (95% CI: 13, 76), respectively. The factor for vegetables is more than twice as high as that for fruit, but the ranges overlap. The ranges were based on the 95% CIs of the serum retinol responses and on the average amounts of retinol and provitamin A carotenoids provided. If we had accounted for the precise variation in carotene content of the foods provided, the differences in the amounts eaten by individual children, and other factors that affect carotene bioavailability and bioconversion, the ranges would have been even larger.

However, when factors are used for converting provitamin A intake to vitamin A, an average value is required. We are confident that the conversion factors we derived represent the general difference between fruit and vegetables. However, as also mentioned in our article, the real conversion factor for specific foods under specific circumstances depends on many factors. Our confidence is based not only on the results of our study. Another study, conducted in breast-feeding women in Vietnam, found similar conversion factors: 12 for fruit and 28 for vegetables (1). The fact that the serum ß-carotene response was better for fruit than for vegetables (5.7 times higher when corrected for the amount of ß-carotene provided) means that the bioavailability of the most important provitamin A carotenoid was better from fruit. Thus, for fruit, bioconversion rather than bioavailability did not seem to have been optimal. Perhaps the conversion rates would be more efficient if the vitamin A status is lower, when the same amount of fruit is consumed in smaller portions throughout the day, or if both conditions exist. Thus, although we agree that serum ß-carotene is not an indicator of vitamin A status, it indicates the potential for increasing vitamin A status when bioconversion could be optimized.

With regard to the remark that the serum retinol concentration is a rather weak indicator of vitamin A status, we note that the currently recommended conversion factors for calculating the retinol equivalence of provitamin A are also based on the results of studies that compared changes in serum retinol concentrations after different sources of vitamin A were consumed. However, as discussed in our paper, the magnitude of the difference and the range of estimates of bioavailability and bioconversion still have to be established more accurately and precisely. This will require the use of other techniques, such as those involving stable isotopes, which are currently being applied in our laboratories (2) and in those of others.

REFERENCES

1. Khan NC, West CE, de Pee S, Khoi HH. Comparison of the effectiveness of carotenoids from dark-green leafy vegetables and yellow and orange fruits in improving vitamin A status of breastfeeding women in Vietnam. Report of the XVIII International Vitamin A Consultative Group meeting. Washington, DC: ILSI, 1997.
2. van Lieshout M, West CE, Lugtenburg J, van Breemen RB, Muhilal. Quantification of bioavailability and bioconversion of ß-carotene using [¹³C₁₀]-ß-carotene and [¹³C₁₀]-retinyl palmitate. Report of the XIX International Vitamin A Consultative Group meeting. Washington, DC: ILSI, 1999 (abstr).

This Article Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by de Pee, S. Articles by Hautvast, J. G. Search for Related Content PubMed Articles by de Pee, S. Articles by Hautvast, J. G. Agricola Articles by de Pee, S. Articles by Hautvast, J. G.