A recently published analyses of research on irisin in the context of its association with age-related problems, including sarcopenia, showed that the evidence is not consistent regarding the association between irisin concentration and health or disease in older adults and indicated the need for further research in this area, taking into account the influence of various factors, including not only age, lifestyle, diet, and ethnicity, but also comorbidities and concomitant medications [20]. The gene discussed is FNDC5; the disease is sarcopenia.