The same development in VO2 max was reported in a parallel SCORE study in Kenya, where the authors suggest that this could be due to an increase in the prevalence of malaria and anemia in the first 2 years of the study.19 However, in the present study, there was an improvement in Hb and reduction in anemia, and, therefore, we suggest that the decrease could be caused by an increase in the body weight of the children. This evidence concerns the gene GSTM1 and anemia.