Diabetes decreased cognitive decline in people with Alzheimer’s disease

People with diabetes and Alzheimer’s disease had a slower rate of cognitive decline when compared with people without diabetes who had Alzheimer’s disease, according to recent data.

“This result was surprising,” Caroline Sanz, MD, of the French National Institute for Health and Medical Research in Toulouse, France, said in a press release. “Our initial hypothesis was that diabetes would increase the rate of cognitive decline in people with Alzheimer’s disease.”

Sanz and colleaues conducted the REAL.FR study — a prospective, multicenter cohort study of patients with Alzheimer’s disease and their caregivers. The researchers followed 608 people with mild/moderate Alzheimer’s disease for four years and tested patients’ memory and thinking skills twice-yearly.

During four years of follow-up, 94 patients died, 76 withdrew consent, 67 were institutionalized, 65 were lost to follow-up, 44 ceased to follow up due to a medical problem of the caregiver and 49 were prevented from follow-up for other reasons.

Diabetes, rate of cognitive decline

Sixty patients reported a diagnosis of diabetes, 44 of whom reported use of antidiabetic medication; three patients were taking antidiabetic medication but did not report a diagnosis of diabetes; 10.4% had diabetes.

Patients with diabetes were more likely to be male (46% vs. 26%; P=.001) and younger (76 vs. 78 years; P=.061) when compared with those without diabetes.

In addition, patients with diabetes were more likely to have hypertension (81% vs. 66%; P=.007), atrial fibrillation (19% vs. 9%; P=.032), coronary heart disease (28% vs. 13%; P=.001), hypercholesterolemia (46% vs. 27%; P=.001), have a higher BMI (26.9 vs. 24.3 kg/m²) and be obese (24% vs. 9%; P<.001).

Although patients with and without diabetes had similar Mini-Mental State Examination (MMSE) baseline scores (–0.75; P=.20), cognitive decline was slower in patients with diabetes (0.38; P=.01).

Further, the mean difference in the rate for six-month cognitive decline between patients with and without diabetes in the unadjusted model was 0.32 MMSE (P=.078) and 0.38 MMSE (P=.01) in the adjusted model. The rate for cognitive decline did not differ between those with diabetes who used insulin vs. those who did not use insulin (0.11; P=.68) or in those with diet-controlled diabetes vs. those taking antidiabetic medications (0.12; P=.65).

The researchers concluded that it is not yet clear why the rate of memory loss was slower for people with diabetes and further studies are needed “to address the potential impact of diabetes and optimized glycemic control in the cerebral aging process.”

“One possible explanation is that diabetes in the elderly differs from that in younger people and older people with diabetes may be more likely to receive cardiovascular medications such as drugs for high blood pressure compared with people who don’t have diabetes,” Sanz said. “These medications have been reported to decrease the risk of developing Alzheimer’s disease and also the rate of cognitive decline in people with Alzheimer’s disease. Other possible explanations for these findings may relate to differences in brain lesions in those people with diabetes compared to those without diabetes.” – by Jennifer Southall

Sanz C. Neurology. 2009;73:1359-1366.

This study is really just a preliminary observation in a very small number of patients that the rate of decline in Alzheimer’s disease in patients with diabetes may be slower than matched controls. There are many variables that need to be controlled for such as glycemic control, different diabetes medications and number and severity of hypoglycemic reactions, and these variables would have to be taken into account with a more rigorous study. Nonetheless, it is nice that having diabetes may be good instead of all the bad news.

– Steve Edelman, MD

Endocrine Today Editorial Board member