This invention provides methods for treating cellular blood components and other cells containing mitochondria to improve vital qualities of the cells by contacting the cells with a mitochondrial enhancer to the cells. Mitochondrial enhancers prevent damage to and rejuvenate mitochondria and cells containing mitochondria. Mitochondrial enhancers include alloxazines and related compounds, such as riboflavin. Cells are optionally treated with photoradiation to reduce pathogens with may be present, before, after, and/or during treatment with mitochondrial enhancer. Treating with mitochondrial enhancer enables utilization of higher photoradiation energies, which achieves better pathogen reduction. When platelets are treated with mitochondrial enhancer, treated platelets may be stored for longer times than untreated platelets before they are administered to patients.