	Irisin (fibronectin type III domain-containing protein 5 or FNDC5), a recently described myokine hormone produced and secreted by acutely exercising skeletal muscles, is thought to bind white adipose tissue cells via undetermined receptors. Irisin has been reported to promote a brown adipose tissue-like phenotype upon white adipose tissue by increasing cellular mitochondrial density and expression of uncoupling protein-1, thereby increasing adipose tissue energy expenditure via thermogenesis. This is considered important, because excess visceral adipose tissue in particular distorts the whole body energy homeostasis, increases the risk of cardiovascular disease and raises exposure to a milieu of adipose tissue-secreted hormones (adipokines) that promote inflammation and cellular aging. The authors enquired whether the favorable impact of irisin on white adipose tissue might be associated with maintenance of telomere length, a well-established genetic marker in the aging process. They conclude that these data support the view that irisin may have a role in the modulation not only of energy balance but also the aging process.