Dietary Antioxidant Intake and Risk of Type 2 Diabetes

Response to Granado-Lorencio and Olmedilla-Alonso

We would like to express our warm thanks to Granado-Lorencio and Olmedilla-Alonso for carefully reading our article (1) and for their comments regarding the inverse association between β-cryptoxanthin intake and diabetes risk (2). Granado-Lorencio and Olmedilla-Alonso pointed out that the β-cryptoxanthin intake in our study population was exceptionally low; therefore, any potential beneficial effect associated with such low amounts of β-cryptoxanthin is difficult to imagine.

In epidemiologic studies, it is difficult to draw conclusions about the absolute amount of a specific nutritional compound necessary for a beneficial health effect. One of the main reasons for this is the fact that nutrient composition tables are under continuing development. A common alternative technique, which we used in the present study, is to rank the study population according to the intakes. In such an approach, the validity of the results depends on the accuracy of the ranking, so absolute intake levels are less important.

In our analyses, the assessment of β-cryptoxanthin intake was based on analyzed values of Finnish foods available in the late 1980s. However, more recent estimates of the β-cryptoxanthin content of oranges have been shown to be much higher than those used in the present study (average orange intake 29 g/day). To ensure the accuracy of our analyses, we recalculated the β-cryptoxanthin intake using more recent published values (3,4). We calculated the κ coefficient between quartiles of the recalculated and the original variables and noted a high level of agreement between these two variables (κ = 0.9), suggesting that the study participants are very similarly ranked using either the original or the recalculated β-cryptoxanthin intake values. Thus, the inverse association between β-cryptoxanthin intake and diabetes risk presented in our article is justified.

In conclusion, we suggest that the significant inverse association between the intake of β-cryptoxanthin and the risk of type 2 diabetes observed in our study is a valid finding. The importance of this finding in the prevention of type 2 diabetes, however, remains to be established.