Diabetes & Cognitive Decline: Any Link?

People who have diabetes diagnosed in midlife have a higher risk of cognitive decline over the following 20 years than people with normal glucose levels, a prospective US study has shown.

Type 2 diabetes has previously been associated with dementia risk, but until now evidence of a link to cognitive decline has been limited.

Researchers followed up 13 351 adults who were aged 48 to 67 at the start of the study in 1990-92 (Rawlings et al., 2014). The participants lived in four US communities (Maryland, North Carolina, Minnesota, and Mississippi) and were taking part in the community-based Atherosclerosis Risk in Communities study.

All participants had their diabetes status assessed at baseline which the researchers defined as self reported diagnosis by a doctor, use of diabetes medication, or having an HbA1c level of 6.5% or greater. Cognitive function was assessed at baseline and then every few years until 2011-13; the 20-year follow-up period making this the longest study yet to investigate its possible links with diabetes.

The results demonstrated that having diabetes in midlife was associated with a 19% greater decline in cognitive function over 20 years (adjusted global z score difference –0.15 (95% confidence interval –0.22 to –0.08)) than not having diabetes. This meant that having diabetes aged cognitive function by about 5-years more than the normal effects of ageing.

People with poorly controlled diabetes (HbA1c>7.0%) showed greater decline in cognitive function than those whose diabetes was well controlled. Further, longer duration of diabetes was associated with a greater cognitive decline in later life.

One of the authors of the study, Elizabeth Selvin (associate professor at the John Hopkins Bloomberg School of Public Health) stated: “The lesson is that to have a healthy brain when you’re 70 you need to eat right and exercise when you’re 50,” and continued “There is a substantial cognitive decline associated with diabetes, prediabetes, and poor glucose control in people with diabetes. And we know how to prevent or delay the diabetes associated with this decline.”

The research group argued that “maintaining cognitive function is a critical aspect of successful ageing,” adding that preventing diabetes and improving glucose control in people with diabetes offered important opportunities for preventing cognitive decline and delaying progression to dementia. “At the population level, delaying the onset of dementia by even a couple of years could reduce its prevalence by more than 20% over the next 30 years,” they concluded.

Reference

Rawlings, A.M., Sharrett, A.R., Schneider, A.L.C., Coresh, J., Albert, M., Couper, D., Griswold, M., Gottesman, R.F., Wagenknecht, L.E., Windham, B.G. & Selvin, E. (2014) Diabetes in Midlife and Cognitive Change Over 20 Years:A Cohort Study. Annals of Internal Medicine. 161(11), pp.785-793.

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