Transitions between metabolically unhealthy and healthy obesity over 27 years from midlife to late-life

Background Metabolically healthy obesity may be a transient phenotype, but studies with long follow-up, especially covering late-life, are lacking. We therefore describe transitions between body mass index and metabolic health (BMIxMH) categories in a sample with up to 27 years of follow-up, from midlife to late-life. Methods We used cohort data from 786 Swedish twins with objective measures of BMIxMH. Metabolic health was defined as absence of metabolic syndrome (MetS). Measurements were categorized into age 50-64, 65-79, or ≥80. Frequencies of transitions between 50-64 and 65-79, and between 65-79 and ≥80 were calculated. One-hundred individuals had measurements in all three age categories, and their dynamic transitions across time were visualized. We also examined frequencies of attrition due to drop-out or death. Results The proportion of individuals with MetS and with overweight or obesity increased over time. However, 28% of individuals with metabolically healthy normal weight and around one fifth of those with metabolically healthy overweight or obesity remained stable across all three age categories. Transitions from MetS to metabolic health were also common, occurring in 7-49% of individuals with metabolically unhealthy normal weight, overweight, and obesity. Drop-out and death during follow-up was comparable across BMIxMH categories. Conclusions Transitions between metabolically healthy and unhealthy categories were relatively common in both directions across all BMI categories. The similar frequencies of drop-outs and deaths indicate that bias due to differences in attrition between BMIxMH categories is not a major issue in this sample.