People with high blood sugar stand to experience worse long-term cognitive decline than their healthy peers, even if they're not technically type 2 diabetic, new research suggests.
The findings are not the first linking diabetes with impaired cognitive functions, but they're some of the clearest yet showing blood sugar isn't just a marker of our dietary health – it's also a telling predictor of how our brains may cope as we get older.
"Our findings suggest that interventions that delay diabetes onset, as well as management strategies for blood sugar control, might help alleviate the progression of subsequent cognitive decline over the long-term," explain the researchers, led by epidemiologist Wuxiang Xie from Imperial College London.
The researchers sourced their data from the English Longitudinal Study of Ageing, an ongoing assessment of the health of a representative sample of the English population aged 50 and older, which began in in 2002.
For its analysis, the team tracked 5,189 participants – 55 percent women, with an average age of 66 years – assessing their level of cognitive function between 2004-2005 to 2014-2015, spanning several waves of the ELSA study.
While all of the participants showed some level of cognitive decline over the course of the assessment due to simply getting older, the researchers found those with greater levels of HbA1c experienced a steepened rate of decline, tracked by tests measuring their cognitive, memory, and executive function abilities.
Interestingly, though, the new findings go beyond just re-establishing the link between diabetes and cognitive decline – because the HbA1c trend was observed in participants regardless of whether or not they were technically diabetic.
Healthy people's HbA1c levels are lower than 42 millimoles per mole (mmol/mol, or below 6 percent), while diabetic people show readings of 48 mmol/mol or above (6.5 percent or above).
In the middle, people with the precursor condition prediabetes (high blood sugar, but not considered diabetic) have readings between 42 to 47 mmol/mol (6 to 6.4 percent).
What the researchers found is that the associated rate of cognitive decline isn't limited to just those who are diabetic, but to higher HbA1c counts generally.
"Our findings show a linear correlation between circulating HbA1c levels and cognitive decline, regardless of diabetic status," the researchers explain.
It's a bit too early to know what the dietary implications are for people concerned about their blood sugar levels – suffice to say it's another compelling reason why we should all be watching what we eat so as to prevent developing type 2 diabetes – although even if you do, some clever choices could help you reverse that diagnosis.
"One strength of this large study is that it followed people over time to show a faster decline in memory and thinking in those with poorer blood sugar control," says Alzheimer's Research UK's Chief Scientific Officer, David Reynolds.
"But it does not shed any light on the potential mechanisms underlying this decline."
While researchers continue to explore what those mechanisms could be, it's becoming clearer that none of us, diabetic or otherwise, should assume diets high in sugar are necessarily harmless to both body and mind.
"Just because you don't have type 2 diabetes doesn't mean you can eat whatever carbs you want," epidemiologist Rosebud Roberts from the Mayo Clinic, who wasn't involved in the study, told The Atlantic.
"Especially if you're not active. [What we eat is] a big factor in maintaining control of our destiny."
The findings are reported in Diabetologia.