Blood Glucose Levels Appear to Affect Motor Skills and Their Decline

Abnormal blood sugar (glucose) levels, either lower or higher than the norm, appears to be linked with a faster progression of motor difficulties in people with Parkinson’s disease, research suggests.

The brief report on this finding, “Euglycemia Indicates Favorable Motor Outcome in Parkinson’s Disease,” was published in the journal Movement Disorders.

Previous research support type 2 diabetes being detrimental to people with Parkinson’s disease. Severe diabetes has been linked with a greater risk of postural instability and poorer gait, as well as more cognitive issues.

However, few studies follow over longer periods of time how motor and cognitive impairment evolve in relation to a person’s blood sugar levels. Researchers at the Karolinska Institute in Sweden, and colleagues, conducted a retrospective analysis to assess how these sugar levels correlate with motor symptom progression and cognitive decline in Parkinson’s patients.

They analyzed the levels of glycated hemoglobin (HbA1c) in the blood of 244 patients (159 men and 85 women, mean age at diagnosis, 64.5) enrolled in an observational study at the Karolinska University Hospital.

HbA1c is formed when hemoglobin, the protein within red blood cells that carries oxygen, is bound to a sugar (glucose) to become glycated. HbA1c is a standard measure of a person’s mean blood glucose level over the preceding 60 days.

According to their levels of blood HbA1c, patients were categorized into one of three groups: those with low-HbA1c (below 30 nanomole per mole, mmol/mol), the with normal HbA1c levels (31–41 mmol/mol), and those with high-HbA1c (at least 42 mmol/mol). HbA1c levels were measured during a median of 3.1 years after a person was diagnosed with Parkinson’s disease.

Patients were followed for a minimum of two years to a maximum of 26 years.

Out of these 244 people, 184 (75.4%) had normal glucose levels (euglycemia), 17 (7%) had low HbA1c levels and 18 (7.4%) had high levels. Twenty-five patients (10.2%) were diagnosed with diabetes.

No differences were found for additional lab parameters, including plasma albumin, an indicator of malnutrition, and body-mass index, a measure of body fat.

Compared to patients with normal HbA1c levels, analyses found that those with low HbA1c were 2.5 more likely to have poorer motor performance. A greater risk of balance problems was seen across follow-up in patients with high HbA1c . These results were maintained even after adjusting for age, sex, and vascular risk factors.

Older age (65 or older) and hypertension were independent predictors of impairments in motor outcomes.

Mild cognitive impairment (MCI), one of the most common non-motor complications of Parkinson’s, was seen in 41% of patients with low and 39% with high HbA1c levels, in 56% of those with diabetes, and in 45% of euglycemic patients.

Patients with HbA1c levels outside the window of euglycemia — meaning those with low and high HbA1c levels — took a median of eight (low) and 6.8 years (high) to reach MCI, and 7.1 years for those with diabetes. In patients with normal HbA1c levels (euglycemia), MCI appeared after a median of 12 years.

Cognitive decline and HbA1c levels, however, did not significant associate after adjustments for confounders like age and vascular risk factors.

“[B]oth high and low HbA1c levels may be associated with motor symptom progression in PD [Parkinson’s disease],” the researchers wrote.

“Further prospective, long-term, follow-up studies and trials on the effect of glucose control modification are needed to better understand this link, and whether glucose homeostasis [equilibrium] could serve as a therapeutic target,” they concluded.