Onset of type 2 diabetes at younger ages appeared to play a role in the risk for dementia, according to results from a longitudinal cohort study published in JAMA.
Previous research has shown that diabetes is a risk factor for dementia only in later life —at 65 years and older — according to Archana Singh-Manoux, PhD, a principal investigator who heads the epidemiology of aging and neurodegenerative diseases team at the University of Paris.
“We were surprised by this conclusion and wanted to know the true impact of diabetes, given No. 1: the increase in prevalence of diabetes and the increasingly younger age of onset of diabetes, and No. 2: the increase in life expectancy implies that more people reach old age, including those with diabetes,” according to Singh-Manoux .
The researchers analyzed data from 10,095 residents in the United Kingdom who had six clinical exams between 1991 and 2016 and electronic health records data spanning through at least March 2019. The participants were aged 35 to 55 years between 1985 and 1988, and 67.3% of them were men.
Singh-Manoux and colleagues reported that 1,710 cases of diabetes and 639 cases of dementia were recorded over a median follow-up of 31.7 years. The dementia rates per 1,000 person-years was 8.9 among those who did not have diabetes at age 70 years, 10 among those with diabetes onset up to 5 years earlier, 13 among those with diabetes onset 6 to 10 years earlier and 18.3 among those with diabetes onset more than 10 years earlier.
In a multivariable-adjusted analysis, compared with participants who did not have diabetes at age 70 years, the HR of dementia among participants with diabetes onset more than 10 years earlier was 2.12 (95% CI, 1.5-3), 1.49 (95% CI, 0.95-2.32) for those with diabetes onset 6 to 10 years earlier and 1.11 (95% CI, 0.7-1.76) for those with diabetes onset 5 years earlier or less. At age 70 years, every 5-year younger age at onset of type 2 diabetes was significantly associated with an HR of dementia of 1.24 (95% CI, 1.06-1.46), after the researchers adjusted for sociodemographic factors, health behaviors and health-related measures.
In this longitudinal cohort study with a median follow-up of 31.7 years, younger age at onset of diabetes was significantly associated with higher risk of subsequent dementia. “The findings are not surprising as younger age at onset of diabetes is known to be associated with higher risk of cardiovascular disease and premature mortality. There is no reason to expect this not to be the case for neurocognitive outcomes,” Singh-Manoux said. “However, most research on dementia is based on older adults, so the age at onset of diabetes is unknown in these studies.”
The findings also add another dimension to the importance of diabetes prevention, according to Singh-Manoux.