The impact of the blade support structures (the struts) on the performance of vertical-axis turbines at a high Reynolds number is investigated here. Numerical simulations of a single-blade turbine with different strut configurations are carried out and the results are compared to a reference hypothetical turbine without strut. The results show that the struts are less detrimental to the turbine efficiency if they are located at the tips of the turbine blade, rather than at other intermediate positions along the blade span. Moreover, for struts located at the blade tips, it is shown that using rounded junctions between the struts and the blade can lead to a significant increase in the turbine efficiency. Indeed, the best turbine configuration presented in this paper has an efficiency that is more than 20% larger than that of the reference turbine without strut. This important increase in the turbine efficiency can partly be attributed to the fact that the tip struts with rounded junctions act as efficient winglets, leading to a significant decrease in the induced drag on the turbine blade. The results presented show that well-designed blade support structures can be very beneficial to the performance of vertical-axis turbines. (C) 2021 Elsevier Ltd. All rights reserved.