Recently, Blankenhaus et al. reported that loss of the iron storage protein ferritin (Fth) impairs thermogenesis in iBAT, possibly due to a dysregulation of systemic iron homeostasis.[25] In our study, genetic iron deficiency mice (Tmprss6 null mice) had a detrimental effect on both cold‐induced beige adipocyte differentiation or CL‐316,243‐activated brown adipocytes. The gene discussed is TMPRSS6; the disease is Iron deficiency anemia.