Future studies should attempt not only to determine whether GDF-15 predicts adverse outcomes in a wider range of older people, but to ascertain whether GDF-15 is part of a causal pathway leading to sarcopenia and dysfunction of other organ systems, whether raised GDF-15 levels actively contribute to protective responses to pathology, or whether raised levels are a bystander marker of other pathological processes (e.g. oxidative stress or other inflammatory signals). Here, GDF15 is linked to sarcopenia.