Letter to the Editor: Dietary Intake with the Transitions of Frailty among Japanese Community-Dwelling Older Adults.

I read, with great interest, the recent article by Rei Otsuka et al. (1). This article’s main result is the association between dairy products and frailty transition. In fact, little research focuses on this association. Thus, the influence of dairy products on frailty is still unclear (2). Although some studies found that dairy products seem to have a preventive effect on frailty among older adults, they all consider causality mainly in terms of nutrition (3, 4). It’s necessary, but two obstacles exist to exploring the association in this way. First, dairy products include nutrients beneficial for frailty prevention, such as protein and calcium. But they also include negative nutrients for frailty, like saturated fatty acid. Besides, dairy product consumption is related to different dietary patterns, which may be beneficial or adverse for frailty prevention (2). As Berna Rahi and his colleagues mentioned, all these effects may be offset interactively (2). Thus, the true association between dairy products and frailty is hard to be exposed. Second, because of the known benefits of some nutrients for many geriatric diseases, it’s difficult to attribute the improvement in frailty to dairy products. For example, in a recent study, Berna Rahi et al. adjusted for total protein intake and didn’t find any association between dairy products and frailty (2). However, this article by Rei Otsuka et al. provided a new perspective. The article found that although there is no difference in average nutrient intake, higher dairy intake is significantly associated with frailty reversal. Thus, it may be linked to health awareness and behaviors associated with high dairy intake (1). This is important to clarify the mechanism between dairy intake and frailty improvement because it suggests that behaviors could be the actual reason for this association, or it could be an important confounder when thinking about the effects of dairy products from a nutritional perspective. However, the authors didn’t conduct further analysis. The following two suggestions may help further explore this hypothesis: First, to analyze the association between dairy intake and changes in each frailty criterion. As the author mentioned, consumption of dairy products declines with age, possibly because it takes a lot of physical effort for older adults to carry them (1). According to it, whether it’s possible that people who consume more dairy have higher physical activity, so frailty improves? Because low physical activity is one of frailty’s five criteria (5). Such assumptions can be discussed in depth by considering changes in each frailty criterion, as can other nutrition-related assumptions. Second, to include more lifestyle factors as covariates in statistical models. If considering behaviors as a potential mechanism between dairy intake and frailty improvement, lifestyles should be considered as potential confounders when analyzing the association between dairy intake and frailty transition in terms of nutritional perspective. However, few studies have done so (2, 3, 4).