Body mass index, waist circumference and pre-frailty/frailty: the Tromsø study 1994-2016

Objective: This study investigated the association between obesity, assessed using body mass index (BMI) and waist circumference (WC), and pre-frailty/frailty among older adults over 21 years of follow-up.

Design: Prospective cohort study.

Setting: Population-based study among community-dwelling adults in Tromsø municipality, Norway.

Participants: 2340 women and 2169 men aged ≥45 years attending the Tromsø study in 1994-1995 (Tromsø4) and 2015-2016 (Tromsø7), with additional BMI and WC measurements in 2001 (Tromsø5) and 2007-2008 (Tromsø6).

Primary outcome measure: Physical frailty was defined as the presence of three or more and pre-frailty as the presence of one to two of the five frailty components suggested by Fried et al: low grip strength, slow walking speed, exhaustion, unintentional weight loss and low physical activity.

Results: Participants with baseline obesity (adjusted OR 2.41, 95% CI 1.93 to 3.02), assessed by BMI, were more likely to be pre-frail/frail than those with normal BMI. Participants with high (OR 2.14, 95% CI 1.59 to 2.87) or moderately high (OR 1.57, 95% CI 1.21 to 2.03) baseline WC were more likely to be pre-frail/frail than those with normal WC. Those at baseline with normal BMI but moderately high/high WC or overweight with normal WC had no significantly increased odds for pre-frailty/frailty. However, those with both obesity and moderately high/high WC had increased odds of pre-frailty/frailty. Higher odds of pre-frailty/frailty were observed among those in 'overweight to obesity' or 'increasing obesity' trajectories than those with stable normal BMI. Compared with participants in a stable normal WC trajectory, those with high WC throughout follow-up were more likely to be pre-frail/frail.

Conclusion: Both general and abdominal obesity, especially over time during adulthood, is associated with an increased risk of pre-frailty/frailty in later years. Thus maintaining normal BMI and WC throughout adult life is important.