Finding prodromal frailty in a community-dwelling healthy older cohort by survey of BDNF or hand grip strength classified by BMI

Abstract

Introduction: Brain-derived neurotrophic factor (BDNF) which is involved in neurogenesis, phenotypic differentiation, and neuronal survival is gaining traction in the field of gerontology research as a relevant factor in cognition and vitality in the older population. Frailty which is losing body weight or lean body mass, experiencing fatigue and loss of strength or endurance, may easily fall and fracture bones, thus becoming hospitalized and bedridden. We studied a distribution of mean BDNF levels or hand grip strengths in the classified BMI, and found the lowest BMI class of thin category has significantly (p<0.01) lower mean BDNF level or mean hand grip strength than in the normal or obese 1 category of BMI.  Therefore we defined the lowest BMI category “thin” as “prodromal frailty”, but not pre-frailty. We will report the findings of “prodromal frailty” and discuss how to prevent this stage from advancing to frailty.

Methods: We measured serum BDNF concentrations, BMI and various health parameters in 805 elderly (aged 65–84) regional health examination participants from the Tokyo area. Their serum BDNF levels and grip strengths were divided according to BMI classification.

Results: The mean serum BDNF levels increased linearly according to BMI categorization from thin (<18.4 kg/m²) to obese2 (30–34.9 kg/m²) and decreased in the obese3 group (35–39.9 kg/m²). The mean serum BDNF level in the thin category was significantly lower than that in the normal category (p<0.01). The BDNF levels in the obese1 and obese2 categories did not differ significantly from that in the normal category. Mean hand grip strength (kg) was also similarly distributed to the mean BDNF level distribution in the classified BMIs.

Conclusions: Elderly people in the thin BMI category had significantly lower serum BDNF levels and weaker hand grip strength than those in the normal or slightly obese categories and the people in this category is so called “prodromal frailty” but not pre-frailty.

Keywords: Frailty, body mass index, brain-derived neurotrophic factor, health examination, hand grip strength