Causes and prevention of frailty
There are two broad models of frailty – these are documented for clarity. The first, known as the Phenotype model 6, describes a group of patient characteristics (unintentional weight loss, reduced muscle strength, reduced gait speed, self-reported exhaustion and low energy expenditure) which, if present, can predict poorer outcomes. Generally individuals with three or more of the characteristics are said to have frailty (although this model also allows for the possibility of fewer characteristics being present and thus pre-frailty is possible). The second model of frailty is known as the Cumulative Deficit model 7. Described by Rockwood in Canada, it assumes an accumulation of deficits (ranging from symptoms e.g. loss of hearing or low mood, through signs such as tremor, through to various diseases such as dementia) which can occur with ageing and which combine to increase the ‘frailty index’ which in turn will increase the risk of an adverse outcome. Rockwood also proposed a clinical frailty scale for use after a comprehensive assessment of an older person; this implies an increasing level of frailty which is more in keeping with experience of clinical practice.
A central feature of physical frailty, as defined by the phenotype model is loss of skeletal muscle function (sarcopenia) and there is a growing body of evidence documenting the major causes of this process. The strongest risk factor is age and prevalence clearly rises with age. There is also an effect of gender where the prevalence in community dwelling older people is usually higher in women. For example a UK study from 2010 using the phenotype approach to defining frailty found a prevalence of 8.5% in women and 4.1% in men aged 65 –74 years 8.
In terms of modifiable influences, the most studied is physical activity, particularly resistance exercise, which is beneficial both in terms of preventing and treating the physical performance component of frailty. The evidence for diet is less extensive but a suboptimal protein/total calorie intake and vitamin D insufficiency have both been implicated. There is emerging evidence that frailty increases in the presence of obesity particularly in the context of other unhealthy behaviours such as inactivity, a poor diet and smoking.
Other areas of interest include the role of the immune-endocrine axis in frailty. For example a higher white cell count and an increased cortisol: androgen ratio predicted 10 year frailty and mortality in one recent study 9.
However the inter-relationship between prescribed medication and frailty independent of co-morbidity is a relatively under-exploited area. There is some evidence that aside from myopathy, some drugs may have more subtle adverse effects on muscle function 10.
The cumulative deficit approach to defining frailty is broader than the phenotype approach, encompassing co-morbidity and disability as well as cognitive, psychological and social factors. The potential causes are therefore wider and include the multiple risk factors which are implicated in the various diseases and conditions.