University College London researchers cast doubt on a causal link between obesity and cognitive decline, saying existing findings are biased by family factors. More than 1.9 billion adults worldwide were overweight in 2016, of which more than 650 million were obese. The World Health Organization warns that number will grow to 167 million by 2025. Previous studies have linked obesity to diabetes, cardiovascular disease, hypertension, osteoporosis, rheumatoid arthritis and cancer.

Obesity has been linked to a plethora of negative health outcomes, including an increased risk of heart disease, stroke, and diabetes. Additionally, research suggests that obesity can also impact cognitive ability, with numerous studies suggesting that those with higher body mass indexes perform worse on tests of memory, attention, and other cognitive functions. However, a new study focusing on siblings has cast doubt on the widely accepted link between obesity and cognitive ability. This article will delve into the study’s findings, examine the implications for our understanding of the relationship between obesity and cognitive ability, and discuss what further research is needed in this area.


Obesity rates have skyrocketed in recent years, with more than 650 million adults globally affected by the condition. Obesity has traditionally been linked with a number of health concerns, including diabetes, cardiovascular disease, hypertension, and more recently, cognitive decline. However, a recent study published in PLOS Medicine by researchers from University College London casts doubt on the link between obesity and cognitive ability. The team compared data from 12,250 siblings from 5,602 households from four separate youth population cohort studies performed in the United States, following each participant from adolescence to age 62. They noted that the existing research literature linking cognitive ability and body mass index (BMI) is biased by shared family factors. By comparing data from siblings, the scientists found that the move from the 25th to 75th percentile of adolescent cognitive ability was associated with only a 0.06 kg/m decrease in BMI. The researchers believe that the smaller association seen in sibling studies could be influenced by downward bias, though this is purely speculative. One factor that may explain the smaller association between cognitive ability and BMI seen within sibling studies is satiety. Dr. Clifford Segil, a neurologist at Providence Saint John’s Health Center, commented on the study, stating that higher cognitive abilities, and higher socio-economic positions are associated with healthier lifestyle choices, and adults with such lifestyles may be more likely to keep a healthy BMI. The researchers suggest that further studies examining whether maternal and paternal BMI affect adolescent cognitive abilities are needed.


While previous studies have suggested a link between obesity and cognitive ability, the latest research involving siblings has cast doubt on this association. The study found that even when siblings had different body mass indexes (BMI), there was no significant difference in their cognitive abilities. This suggests that genetics and other factors may play a greater role in cognitive ability than weight alone. While maintaining a healthy weight is important for overall health, this study highlights the complexity of the relationship between weight and cognition. Further research is needed to fully understand this connection, and to identify effective interventions for improving both weight and cognitive function.