Saliva testing may reveal early signs of metabolic disease

The University of British Columbia (UBC) Okanagan team has found that measuring insulin levels in saliva offers a non-invasive way measure metabolic health and can show the risk of developing future health concerns, including type 2 diabetes, obesity and heart disease - without the need for needles or lab-based blood work.

Dr Jonathan Little, Professor with UBC Okanagan's School of Health and Exercise Sciences, said the simple spit test could also be used to detect early metabolic changes linked to obesity and other health risks. The study included 94 healthy participants with a range of body sizes. After a period of fasting, each participant drank a standardised meal-replacement shake, then provided saliva samples and underwent a finger-prick blood glucose test.

Jonathan Little (Credit: UBC)

"People living with obesity had much higher insulin levels in their saliva than those who were slightly overweight or had lower body weight, even though their blood sugar levels were the same," Little explained. "This suggests that saliva testing could be a simple, non-invasive way to identify people at risk of type 2 diabetes before symptoms appear."

Little notes that prediabetes conditions, such as insulin resistance and hyperinsulinemia, may develop ten to 20 years before a person is diagnosed.

"If hyperinsulinemia can be detected before blood glucose levels start to rise, people at risk for type 2 diabetes could be identified early, allowing for lifestyle changes and other treatments to be introduced long before glucose levels rise."

Taking preventive steps at an early stage is important because hyperinsulinemia is a known predictor of several chronic conditions, including type 2 diabetes, hypertension, cardiovascular disease, stroke, cancer, and most recently, it has been linked to obesity.

Co-author, Dr Hossein Rafiei added that the study aimed to help develop a practical non-invasive test for hyperinsulinemia, but they also found an interesting result following the consumption of the meal-replacement drink. Previous research at UBC Okanagan showed that saliva insulin levels closely follow plasma insulin levels across the day following high and low-carbohydrate mixed meals.

"This suggests that saliva insulin may help distinguish between high and low plasma insulin responses, and could play a role in predicting the severity of hyperinsulinemia and possibly insulin resistance."

During the study, participants provided saliva tests 30, 60 and 90-minutes after drinking the beverage.

Rafiei noted that, interestingly, some participants with lower body weight also experienced large saliva insulin spikes after the meal. This suggests they may be at heightened risk for type 2 diabetes, even without excess weight and having normal blood glucose levels.

"The finding that some people who are lean have high insulin is intriguing," said Rafiei. "This indicates that saliva insulin may be more useful than measuring someone's weight or waist size."

The study also looked at the relationship between waist circumference, BMI, age and sex, and found that waist size had the strongest link to saliva insulin levels.

"These findings suggest that waist circumference could be a more reliable indicator of hyperinsulinemia than age or overall body weight when using saliva insulin," he says. "Our results also suggest that saliva insulin may be better than blood glucose at distinguishing between those who are more metabolically healthy and those who are more likely to live with hyperinsulinemia."

The findings were reported in the paper, ‘Saliva insulin concentration following ingestion of a standardized mixed meal tolerance test: influence of obesity status’, published in the journal Applied Physiology, Nutrition, and Metabolism. To access this paper, please click here (log-in maybe required)