In this prospective women’s cohort adherence to Mediterranean diet was found to be associated with lower risk of frailty in those admitted to hospital, with a dose-response showing greater adherence associated with lower risk. Although different measurement tools were used, our results are consistent with the main evidence of a meta-analysis and systematic review which showed a 38% reduction in frailty risk by medium adherence to Mediterranean diet, and a 56% reduction by high adherence using FRAIL scale or Modified Cardiovascular Health Study frailty criteria (mCHS) [6]. Similar associations can also be observed in other areas and male populations. Among 15,249 men and women in US, Mediterranean diet score was inversely correlated with the frailty index [19]. A Greek longitudinal study recently reported that each unit of Mediterranean diet score was associated with a 5% or 10% decrease in the risk of incident frailty when the Frailty Index and the Tilburg Frailty Indicator used respectively [20]. Those findings together imply a protective association between adherence to Mediterranean diet and risk of frailty, irrespective of measurement tools used, or populations investigated.
Stratified analyses showed there was some evidence of effect modification by age and BMI, where differences in associations were observed between separate age groups and BMI groups. A similar effect modification by age was also reported in the Framingham Offspring Study, where lower risk of frailty in relation to per unit higher Mediterranean diet was stronger in participants aged < 60 years compared to those aged ≥ 60 years [21]. In our study, there was no evidence that moderate adherence to the Mediterranean diet was associated with risk of frailty in the ≥ 60-year, which was similarly observed in the prospective Seniors-ENRICA-1 cohort (≥ 60 years) [22], the Italian InCHIANTI cohort (≥ 65 years) [23], and the French Three-City cohort (≥ 75 years) [24], whereas high adherence was associated with up to 74% lower risk of frailty in those studies. The inverse association between adherence to Mediterranean diet and risk of frailty potentially changes during aging, which may be more obvious in relatively younger groups such as those less than 60 years of age. Suggesting that elderly people should adopt the Mediterranean-type diet closely if considering risk of frailty. In addition, our results showed higher magnitude of associations among individuals with being normal-weight compared to being overweight, implying that weight management is potentially an important consideration in controlling risk of frailty related to Mediterranean diet. However, since evidence on effect modification of BMI in associations between Mediterranean diet and frailty risk is limited, further related research is needed.
The rationale for the association between Mediterranean diet and frailty risk remain unclear. One potential mechanism may be the benefits of Mediterranean diet in affecting various chronic health outcomes. Previous evidence has shown that higher adherence to Mediterranean diet was associated with lower risk of several non-communicable chronic diseases (NCDs) including cardiovascular diseases, cancer, cognitive decline, fragility fractures, etc. [25]. Some frailty assessment tools such as frailty index [10] and hFRS [11] measure the cumulative state of chronic diseases which are the basis of frailty. A lower incidence of numerous age-associated NCDs may help to explain the benefit of a Mediterranean diet regarding frailty. The Mediterranean diet is considered to be a healthy, plant-based diet. Plant-based diets are found to be protective against frailty risk [26]. Besides, high consumption of fruits and vegetables, the main sources of antioxidants [27], has been associated with lower risk of frailty [28, 29]. In addition, some previous epidemiological studies reported a protective association of a Mediterranean-type diet rather than one food group alone with risk of frailty [30], indicating the potential interactive or additive action between “healthy foods” that may prevent the pathogenesis of frailty.
This study has some limitations. First, the prevalent cases of frailty could not be excluded at baseline since hospital records at recruitment were not available for analysis. However, in our sensitivity analyses results were robust to exclusion of participants with a survival time < 3 years, with two or more chronic diseases, or with long-term treatment for illness. Second, in the primary analysis cases of frailty in this study were not differentiated on the basis of severity. Cases of mild frailty (possible pre-frailty) were therefore included, potentially attenuating associations. Nevertheless, additional analyses using a stringent standard as the cut-point (≥ 2 score) were conducted as supplementary results and yielded broadly similar results. This study is also weakened by participants being only women, and those admitted to hospitals in England rather than other parts of the UK, which limits generalizability of our findings; therefore, further research is required in other populations.
Strengths of this study comprise the high quality of diet assessment via a validated comprehensive FFQ, a long follow-up prospective cohort study design with a large sample size, and efficient frailty measurement based on linkage data with national hospital diagnostic records. Currently, there are few measurement tools for assessment of frailty in hospital settings, our study provided some evidence for the possibility of using hFRS to assess in-hospital frailty. In contrast to other studies, our study additionally explored effect modifications of age and BMI on associations between Mediterranean diet and frailty risk, which makes the findings more precise and targeted.
Overall, our study suggested a protective association between adherence to Mediterranean diet and risk of frailty, particularly in those of younger age and normal weight. These findings will provide useful insights for developing future intervention programs to encourage healthy population aging.