The purpose of this study was to evaluate whether a low intake of energy and nutrients is associated with frailty in older persons. We found that having an intake of energy ≤21 kcal/kg/day was associated with frailty, and a low intake of more than three nutrients (poor nutritional score) was significantly associated with frailty, independent of energy intake and other potential confounders. Poor nutritional score was associated with feeling of exhaustion and poor muscle strength, which are frailty criteria. After adjusting for energy intake, however, the association with feeling of exhaustion was no longer statistically significant, indicating that low energy intake may lead to exhaustion. Instead, the association with poor muscle strength remained significant, suggesting that the quality of diet plays an important role in muscle efficiency.
The link between nutrition and frailty likely involves multiple pathophysiologic pathways. For example, energy and nutrient deficiency may affect mitochondrial function leading to muscle-related symptoms, including fatigue and weakness (7
); protein intake is the major factor responsible for muscle protein anabolism in older persons (17
); unopposed oxidative stress may be detrimental for skeletal muscle (18
); and antioxidant vitamins may play a preventive role in reducing oxidative injury (20
). Our previous study (22
) suggested that a deficiency of antioxidants is associated with reduced muscle strength. Accordingly, we found here that low intakes of vitamins E and C were associated with frailty, independent of protein and energy intake. Our finding of an association between low intake of vitamin D and frailty is also interesting given that a considerable number of vitamin D receptors are located on the surface of muscle cells (23
Overall, our findings suggest that poor nutritional intake is an important factor associated with the frailty syndrome. A low intake of nutrients is associated with frailty even independent of energy intake. There are important implications with this finding. First, the quality of diet expressed by the intake of specific nutrients is an important factor affecting the health of older persons, and a low intake of specific nutrients may contribute to the development of the frailty syndrome. Second, this study suggests that weight loss may not be a sensitive proxy measure of inadequate diet, and the assessment of nutritional intake may be useful as part of the screening, diagnosis, and treatment of the syndrome.
An important strength of this study is the low number of persons in our sample (4%) who used nutritional supplements; this validates our findings. When we repeated the analysis excluding those participants who used supplements, the results were not substantially changed.
To our knowledge, this is the first study to evaluate the relationship between dietary intake deficiency and frailty, considering as the reference an operational definition of frailty (2
), and using a population-based sample including a large number of older persons. Previous studies considered nutrition as an important domain in the pathogenesis of frailty, but most of them used weight loss as proxy measure of undernutrition, included disabled persons, and included hospitalized or institutionalized participants (24
). Consequently, those findings cannot be extended to the general older population.
The most important limitation of this study is its cross-sectional nature; this makes impossible to establish a causal role of low intake of nutrients in frailty. In a previous study, we found that having physical and cognitive limitations were associated with increased risk of having inadequate dietary intake (26
). We tried to minimize the effect of reverse causality in this study by excluding disabled participants and those participants with severe cognitive impairment (MMSE <18).
This study provides evidence that low intakes of energy and specific nutrients are associated with frailty. By using nutritional intake, it may be possible to target older persons at an early stage of frailty, before changes in body composition, biochemical markers, and their consequences become clinically evident and likely irreversible. Moreover, weight loss and altered biochemical markers may be caused by different factors (diseases, reduced absorption, metabolism, or inadequate diet); therefore, the best strategy for their treatment remains uncertain. Our results bridge this gap and open a potential avenue for the prevention of frailty: Nutritional intake is certainly an important factor.