Steps in the right direction for physical frailty research

In this issue of The Lancet Digital Health, Rongtao Jiang and colleagues present a broad and well powered observational study of the correlates of physical frailty among nearly half a million middle-aged and older adults in the UK Biobank. Using a modification of the Fried frailty phenotype (based on weakness, walking speed, inactivity, exhaustion, and weight loss), the strongest correlates of participants' mainly self-reported frailty status were other aspects of self-reported health and wellbeing, as well as neuroticism, anxiety, and depression. Importantly, many of the associations reported were of relatively small effect size. These results were similar between the sexes and across much of the age range, with the exception of mental health measures, which were more strongly associated with frailty in middle age than in older adults. In longitudinal analyses, stronger associations were found between baseline health (particularly mental health) and frailty measured 9 years later than for the converse specification. The results also show widespread but small brain structural correlates of frailty, which mediated less than 2% of the association between physical frailty and the top ten frailty-related phenotypes.