“Our study suggests that there may be cognitive consequences to earlier onset type 2 diabetes, and it points to the need for strategies to prevent dementia that consider both diabetes and obesity,” said Xiang Qi, assistant professor at NYU Meyers and the study’s first author.

Type 2 diabetes is a known risk factor for dementia. Although the underlying mechanisms are not fully understood, scientists think that some of the hallmarks of diabetes — such as high blood sugar, insulin resistance, and inflammation — may encourage the development of dementia in the brain.

While type 2 diabetes was once a disease of older adults, it is increasingly prevalent among younger individuals: one in five people with type 2 diabetes worldwide is under 40 years old.

To understand how the timing of a type 2 diabetes diagnosis relates to dementia risk, the research team analyzed data from 2002 to 2016 in the Health and Retirement Study, a longitudinal study conducted by the University of Michigan Institute for Social Research. The PLOS ONE study included 1,213 U.S. adults aged 50 and over with type 2 diabetes confirmed by blood tests — and no dementia upon joining the study. Following participants for up to 14 years, 216 (17.8%) developed dementia based on follow-up telephone interviews.

The researchers found that adults diagnosed with type 2 diabetes at younger ages were at increased risk for developing dementia, compared to those diagnosed at 70 years or older. Adults diagnosed with diabetes before age 50 were 1.9 times as likely to develop dementia as those diagnosed at 70 and older, while those diagnosed between 50-59 years were 1.72 times as likely and those diagnosed between 60-69 years were 1.7 times as likely.

Using linear trend tests, the researchers found a graded association between age at diagnosis and dementia risk: for each year younger a person is at the time of their type 2 diabetes diagnosis, their risk for developing dementia increases by 1.9%.

“While we do not know for sure why an earlier diabetes diagnosis would increase the risk for dementia, prior studies show that people diagnosed with type 2 diabetes in mid-life may experience more vascular complications, poor blood sugar control, and insulin resistance — all of which are known risk factors for cognitive impairment,” said Bei Wu, the Dean’s Professor in Global Health and vice dean for research at NYU Meyers and the study’s senior author.

In addition, obesity appeared to influence the relationship between type 2 diabetes and dementia. Individuals with obesity who were diagnosed with type 2 diabetes before age 50 had the highest dementia risk in the study.

The researchers note that this greater understanding of the connection between diabetes onset, obesity, and dementia may help inform targeted interventions to prevent dementia.

“Our study highlights the importance of one’s age at diabetes diagnosis and suggests that specifically targeting obesity — whether through diet and exercise or perhaps medication — may play a role in staving off dementia in younger adults with diabetes,” said Wu.

In addition to Qi and Wu, study authors include Zheng Zhu of NYU Meyers, Huabin Luo of East Carolina University, and Mark D. Schwartz of NYU Grossman School of Medicine. The research was supported in part by the National Institute of Aging (P30AG083257, R56AG067619) and National Institute of Minority Health and Health Disparities (P50MD017356).