A recent study has found that frequent, dramatic fluctuations in weight during middle age may increase the risk of early-onset dementia.

Researchers at Seoul National University Bundang Hospital (SNUBH), led by Professor Ryu Ji-won from the Department of Internal Medicine and Professor Yoon Hyung-jin from the Department of Biomedical Engineering at Seoul National University College of Medicine, analyzed data from more than 3.6 million individuals aged 40 to 65 enrolled in Korea’s National Health Insurance Service.

The study explored the link between "weight cycling" —repeated patterns of weight gain and loss—and its potential link to early dementia.

Sudden changes in weight during middle age are often seen as warning signs of potential health issues. Rapid weight gain or loss has been associated with various severe conditions, including cancer, cardiovascular disease, diabetes, weakened immune systems, osteoporosis, and cognitive disorders such as dementia. Larger weight fluctuations have also been linked to increased mortality rates.

While previous studies have mainly focused on one-directional weight changes—either gaining or losing weight—the SNUBH research team analyzed the relationship between weight cycling, including patterns of weight gain followed by loss and vice versa, and the prevalence of dementia, examining both the magnitude and frequency of these cycles.

They tracked patients who had undergone at least five health checkups over a one- to two-year period, analyzing data from a 10-year follow-up. Patients were categorized into four groups based on their weight fluctuations: more than 3 percent, 5 percent, 7 percent, and 10 percent from their previous weight.

The findings revealed that patients who experienced weight fluctuations of more than 3 percent had a 1.2 times higher risk of developing dementia compared to those with less than 3 percent variation. The risk doubled for those with swings of more than 10 percent. The average age of dementia onset was 58, which falls within the early-onset category.

Further analysis showed that individuals who experienced weight fluctuations of more than 10 percent at least twice during the 10-year observation period had a 2.5 times higher risk of dementia. This risk was found to be particularly pronounced in individuals with a body mass index (BMI) of 25 or higher, compared to those with a lower BMI.

The study suggests that frequent and significant weight cycling—whether due to regaining lost weight or rapid weight loss following gain—can negatively impact brain health and increase the likelihood of early-onset dementia.

“This research highlights the importance of raising awareness about weight management,” said Professor Ryu. "Excessive weight fluctuations can place metabolic stress on the body, so maintaining a stable weight within a healthy range should be a focus, particularly for those in middle age and beyond.”

The full study detailing these findings was published in the international journal Alzheimer’s Research & Therapy.