Associations of Birth Size with Physical and Cognitive Function in Men and Women 60 Years and Older—Systematic Review and Meta-Analysis

Background/Objectives: This systematic review aimed to investigate the relationship between birth size, a marker of prenatal undernutrition, and both physical and cognitive function in individuals aged 60 years and older. Methods: We searched the PubMed and Scopus databases up to November 2024 for prospective cohort studies that included data on birth size and physical or cognitive function in individuals aged 60 or older, excluding studies focused on preterm individuals. The Risk Of Bias In Non-randomized Studies—of Exposure (ROBINS-E) tool was used to evaluate the bias of each included study. Fixed-effects meta-analysis was performed using Review Manager. This systematic review was registered with PROSPERO, CRD42023360823. Results: Twenty-four articles met the eligibility criteria, with participant numbers ranging from 52 to 4000 (about 50% women) and an average age range of 60.9 to 78.4 years. Eight articles had a high risk of bias, while the remaining 16 presented some concerns. Three meta-analyses were conducted: two for grip strength and one for word fluency. Grip strength was positively associated with birth weight, both in an unadjusted analysis, which showed an increase of 1.88 kg (95% CI 1.19, 2.56), and in an analysis adjusted for age, sex, and height/body mass index, which showed an increase of 1.15 kg (95% CI 0.71, 1.59). Word fluency also displayed a positive association with birth weight, with an increase of 0.62 words per minute (95% CI 0.15, 1.10). Conclusions: Smaller birth size, indicative of prenatal undernutrition, is associated with diminished physical and cognitive function in later life. These results highlight the importance of identifying individuals born small as a vulnerable group and implementing lifelong strategies to promote healthy aging.