An important limitation to the current evidence base that links nutrition to sarcopenia is that much of the observational data are from cross-sectional studies. Aside from methodological considerations of studying older adults who may have a number of comorbidities, this raises particular issues that may limit our understanding of the potential importance of the role of nutrition in the loss of muscle mass and strength with age.
Firstly, the health of older people is influenced by events throughout their lives [10
], and achievement of optimal function may, therefore, depend on lifelong exposure to a healthy diet and lifestyle. Although there is evidence that healthier eating behaviours are reasonably stable in adult life [42
], little is known of changes in dietary habits in older people, at a time when morbidity-related dietary advice is available, and lifestyle may be changing rapidly. The influence of lifelong nutrition on age-related changes in muscle mass and strength has been little studied, but in terms of interventions to delay or prevent sarcopenia in older age, there may be key opportunities earlier in the lifecourse that need to be recognised.
A second consideration is that muscle mass and strength achieved in later life are not only determined by the rate of muscle loss, but also reflect the peak attained in early life (, [43
]). Thus, factors that influence growth, such as variations in early nutrition, may contribute to muscle mass and strength in older age.
Figure 1 A lifecourse model of sarcopenia (from ).
A key finding, that highlights the importance of lifecourse influences, is that low weight at birth predicts lower muscle mass and strength in adult life. This is a consistent finding across a number of studies [44
]. Although little is currently known about the influence of diet in early life on sarcopenia, recent studies of adolescents have provided evidence of nutrient effects on muscle mass and function earlier in the lifecourse. Consistent with studies of older adults, low vitamin D status has been shown to be associated both with lower grip strength and with poorer muscle power and velocity [45
]. However, randomized controlled trials of vitamin D supplementation of adolescents have had mixed results. Among premenarcheal girls who were supplemented with vitamin D over 1 year, there were graded increases in lean mass, although supplementation did not result in measurable differences in grip strength [47
]. In contrast, vitamin D supplementation of adolescent boys and postmenarcheal girls has not been shown to be effective in increasing lean mass or muscle strength or power [47
]. Ward et al. [48
] conclude that earlier interventions, before the period of peak muscle mass accretion, may be needed to improve muscle function and physical performance.
To date, few studies have examined the role of diet in early childhood in the acquisition of muscle mass and effects on later function, although there is some evidence that it could be important. For example, the risk of frailty has been shown to be greater in older adults who grew up in impoverished circumstances, and who experienced hunger in childhood [49
]. However, animal models suggest that nutrition even earlier in life may be key, as muscle growth in the neonatal period is highly sensitive to variations in nutrient intake [50
]. In two recent studies, the role of variations in infant diet has been addressed, but with differing results. Among children in the ALSPAC study, duration of breastfeeding was not associated with physical work capacity assessed at the age 9 years [51
], whilst in adolescents studied in the HELENA cohort, longer duration of breastfeeding was associated with measurable differences in physical performance–particularly in lower body explosive strength [52
]. Consistent with these latter findings, longer duration of breastfeeding and greater compliance with infant feeding guidance has been shown to be associated with greater lean mass in later childhood [53
]. Dietary patterns “track” across childhood [54
], and this may simply reflect continuing benefits of healthier diets. However, it does suggest that variations in early postnatal diet could have implications for muscle function in later life.
We currently know little about the contribution of nutrition across the lifecourse to muscle mass and strength in adult life, and further work is needed to understand how early nutrition influences the acquisition of peak muscle mass, and the role played by nutrition in the trajectory of age-related losses in muscle function. Taking a lifecourse approach to understanding the links between nutrition and muscle mass and function in older age could change dietary strategies to prevent sarcopenia in the future.