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DISCUSSIONIn this supplementation experiment, in which iron was given to primary schoolchildren in southern Thailand for 16 wk, comparableeffects between once weekly and daily supplementation were found in both change in Hb and reduction of the prevalence of IDA.The daily group had a significantly greater SF than the other two groups, but significantly lower height gain than the weeklygroup. Neither supplementation regimen showed an effect on weight gain, change in weight-for-age or change in height-for-age.
During the supplementation period, the mean Hb improvement seen in the placebo group may have been due to various causes suchas deworming, shift in age among children or some unknown effect of the follow-up. After allowing for the placebo effect,the net gain of Hb in the daily and weekly groups was 3.1 and 2.3 g/L, respectively, in 16 wk. The poor response to iron supplementationin these subjects may be attributable to the low prevalence of IDA or to the thalassemia trait, which exists in the southernThai population (19).
Our study was confined to 16 wk of supplementation. However, the real supplementation program will be implemented year round.The findings that the daily dose yielded a higher SF than the weekly dose may simply reflect a slower increase of SF. Prolongedweekly dosing may eventually lead to adequate saturation of iron in blood and in tissue.
To our knowledge, only two previous studies (13,14) have assessed intermittent iron supplementation as a blanket supplementation, that is, including both anemic and nonanemicsubjects as in our study. A study of weekly iron supplementation among Tanzanian adolescents (14) found a significantly greater increase in serum ferritin compared with a vitamin B-12 control group, but there was no significantdifference in change in Hb. However, a study in Peru (13) found that a 17-wk daily supplementation led to significantly higher Hb increases than twice weekly supplementation; however,SF and free erythrocyte protoporphyrin were similar in the two groups. It is possible that the 60 mg iron/d given to adolescentswhose average weight was almost 50 kg may be too small a dose to improve Hb and correct anemia in the intermittent schedule;the actual values of SF were not shown in that paper.
Our study found no significant difference in weight gain, change of weight-for-age, or change of height-for-age among weekly,daily and placebo groups, but a significantly greater height gain among children receiving once weekly iron supplementationthan that in the daily group. The patterns of height gain and change of height-for-age were consistent (i.e., worst in thedaily group and best in the weekly group), but a significant difference was detected only in height gain. The lack of significancein height-for-age may be due to the lower precision of this variable. Almost 50% of our subjects had a height exceeding thelimit for calculation of weight-for-height; thus, we omitted this anthropometric index.
Studies regarding the effects of daily iron deficiency upon growth have shown inconsistent results. Studies in India, Kenyaand Indonesia found an improvement in growth after iron supplementation (22"25). Improved appetite and decreased morbidity were the explanations given in those studies for enhanced growth after iron supplementation.Studies in Mexico, Bangladesh and Thailand, however, reported no benefit of iron supplementation on growth (26"28). One proposed explanation is that deficiency of multiple micronutrients such as zinc and vitamin A could have limited thegrowth response to iron (27). Furthermore, a report of the adverse effect of iron on weight gain in children with adequate iron status has raised concernsamong public health researchers about giving supplemental iron to children (29).
We could find only one previous study comparing weekly iron supplementation with daily dosing on growth. This study on Indonesianprimary schoolchildren (10) reported no significant differences in increases of weight-for-age, weight-for-height or height-for-age after 3 mo of weeklyand daily iron supplementation among anemic schoolchildren.
Using subjects in a different age group, a study among Tanzanian adolescent girls comparing weekly iron supplementation anda vitamin B-12 control group reported a significantly greater weight gain in the weekly iron supplemented group than in thevitamin B-12 control group after 4 mo of supplementation (14).
Iron intake in our study was observed closely, and >90% of children received complete iron supplementation. Thus, the lackof significant difference in some of the outcome measurements among the groups cannot be explained by low compliance.
The immediate goal of the iron supplementation program in Thailand is to reduce the prevalence of anemia and increase tissueiron concentration, on the assumption that this will improve the health and performance of the children. Our data suggestthat the goal of iron saturation is better achieved with daily rather than weekly supplementation but the potential adverseeffect on growth (height gain) should be taken into consideration.