Dual trajectories of insomnia symptoms and BMI and their associations with cognitive functioning

INTRODUCTION: Insomnia symptoms and high body mass index (BMI) are separately associated with poorer cognitive functioning. However, little is known about dual associations of sleep and obesity, and the changes in subjective cognitive functioning. We used a person-oriented approach to identify these dual trajectories and their associations with changes in subjective cognitive functioning. METHODS: Repeated surveys of the Helsinki Health Study (n = 2360, 79% women,40-60 years at baseline) were used to identify developmental patterns of insomnia symptoms and BMI (2000-2017) and changes in subjective cognitive functioning (2017-2022). Subjective cognitive functioning was inspected in three dimensions: memory, concentration, and learning ability problems. Latent group-based dual trajectory modeling and logistic regression analysis were used. RESULTS: Regarding dual trajectories of insomnia and BMI, three latent groups were selected for each. Insomnia symptoms defined as: stable low, decreasing and increasing symptoms; and BMI as: stable healthy weight (BMI < 25), stable overweight (BMI 25-29.9) and stable obesity (BMI ≥ 30). While BMI and insomnia symptoms can develop together, this study suggests that the higher likelihood of reporting poorer memory, concentration, and learning ability problems, is explained by insomnia symptoms at all levels of BMI. Thus, BMI was not associated with cognitive functioning, while increasing insomnia symptoms were associated with poorer perceived cognitive functioning for all measures examined (odds ratios ranged from 1.8 to 2.9, all statistically significant) CONCLUSIONS: Dual development of insomnia and overweight is possible, but only insomnia seems to be associated with changes in subjective cognitive functioning at all BMI levels. A potential intervention point to prevent or postpone cognitive decline in later life starts likely years or even decades before retirement, when the risk factors emerge or start to increase. KEY MESSAGES: • The association between dual trajectories of insomnia symptoms and BMI and subjective cognitive decline is dominated by insomnia symptoms. • Our results showed that developmental patterns of insomnia symptoms are associated with decline in subjective cognitive functioning.