In our study, simulated zinc intake from biofortified rice at two levels of zinc resulted in an increase in total zinc intake and a decrease in the prevalence of insufficient zinc intake in an adult population. Rice was the most important staple food in our study population, with 95% of subjects eating rice daily. Only 0.1% of the participants would have excessive zinc intake with rice biofortified at the highest level (3.8 mg/100 g).
There are some limitations in the present study that should be mentioned. Firstly, day-to-day variation is the main random error of dietary recall, which we have minimized by using 3-day 24 h dietary recalls, including two weekdays and one weekend day, in addition to a validated FFQ conducted by well-trained interviewers. Nevertheless, over- or underreporting may have occurred resulting in misclassification, thereby weakening the associations under study. Secondly, since data on dietary phytate was not available, we could not calculate the exact bioavailability of zinc for each individual. Instead, we have assumed that the mixed diets of people in Jiangsu Province are inhibitory for zinc absorption at the intermediate level based on the suggestions by IZiNCG [9
]. When estimating intake of absorbable zinc, the adequacy of absorbed zinc intake was very similar to insufficiency of total zinc intake. Moreover, we used a cut-off of 2/3 Chinese RNI for assessment of insufficient zinc intake. This cut-off corresponds well with the IZiNCG EAR at the age of 18–49 years [9
]. Thirdly, a common limitation for factor analysis is arbitrary decisions in determining the number of factors to retain and in labeling food patterns [20
]. Also, a causal relationship between dietary pattern and insufficient zinc intake cannot be derived from this cross-sectional study.
The use of simulated zinc intake in the design of programs for micronutrient fortification or biofortificaiton is limited. Consistent with our report, a Mexican study showed that simulated biofortification of maize and beans with additional amounts of zinc resulted in a significantly decreased prevalence of inadequate absorbed zinc intake [18
]. Subjects in our study consumed 12 mg/day of total dietary zinc and 3.6 mg/day of estimated absorbed zinc, and the prevalence of insufficient zinc intake and absorbed zinc inadequacy was around 15%–16%. Mexican women, however, only consumed 1.68 mg/day of absorbable zinc, and the prevalence of absorbed zinc inadequacy was between 40% and 50% [18
]. Like our study, Arsenault et al
] also reported the effect of simulated increases in the zinc content of rice on improvements in total dietary zinc adequacy in rural Bangladeshi children and women In the women, mean intakes of total zinc and absorbed zinc after simulation were 5.5 and 1.3 mg/day, with a prevalence of absorbed zinc inadequacy of 76%–99.8%, compared with 100% at baseline [17
]. The discrepancies between studies show that the effect of biofortification depends on the magnitude of zinc deficiency in a specific population. Moreover, differences in the simulated amount of zinc from biofortification may also result in different effects. In the Bangladeshi population, an additional 0.8 mg of zinc/100 g of rice (raw weight, with unknown baseline zinc concentration) was added [17
], whereas we added 1.0 mg/100 g and 2.1 mg/100 g in our simulations. The modest increment of zinc in rice may have contributed to the remaining high prevalence of absorbed zinc inadequacy in the Bangladeshi study.
Biofortification of rice provides a potential approach to improve zinc intake in populations with rice as a staple food, because it does not require a change in the choice of staple foods. Since the phytate/zinc molar ratio is lower than 15 in rice in China [27
], it can be expected that zinc from rice is well absorbed. For this study, we have used two levels of biofortification: 2.7 mg/100 g and 3.8 mg/100 g. The latter level was derived from biofortified rice that has been grown at Wageningen University on Zn-fortified solution culture medium in a greenhouse (unpublished results). It still needs to be shown whether this high level of biofortification can also be reached under field conditions, although there is some evidence [28
]. Since a biofortified staple food is more difficult to adjust to the specific needs of populations than commercial fortified foods [12
], it is very important to set efficacious target breeding levels. According to our simulations, the largest reduction in prevalence of zinc intake insufficiency was achieved with the intermediate level of zinc. Therefore, a level of 2.7 mg/100 g may be set as preliminary goal for the first phase of development of biofortified rice, which is very close to the target zinc content in rice (2.8 mg/100 g) that has recently been recommended by HarvestPlus [28
With respect to dietary patterns, the positive effect of biofortification on dietary zinc was much more significant in the highest quartile of the “traditional” pattern, which can be attributed to the higher intake of rice in this population segment. In contrast, there was an inverse trend between zinc intake and the “sweet tooth” pattern. High intake of beverages, milk and cake may contribute to poor zinc intake. Zinc concentrations have been reported to be low in distilled drinks and milk [9
]. Moreover, calcium is abundant in milk, which may have an inhibitory effect on zinc absorption [32