Saliva insulin test: a non-invasive method for early diagnosis of metabolic disorders

Measuring elevated levels of insulin in the blood, called hyperinsulinemia, is a proven way to assess metabolic health and may indicate the risk of developing future health problems such as type 2 diabetes, obesity and heart disease.

Now, a team of researchers from UBC Okanagan has found that measuring insulin levels in saliva offers a non-invasive way to perform the same test - without the need for injections or lab blood tests.

Dr. Jonathan Little, a professor at UBC Okanagan's School of Health and Exercise Sciences, says the simple saliva test goes further. It could also be used to detect early metabolic changes linked to obesity and other health risks.

The study, recently published in the journal Applied Physiology, Nutrition, and Metabolism, involved 94 healthy participants with varying body sizes. After a period of fasting, each participant drank a standard nutritional shake, then provided saliva samples and underwent a finger-prick blood glucose test.

“People who were obese had significantly higher levels of insulin in their saliva than those who were only slightly overweight or normal weight – even though their blood sugar levels were the same,” he says. “This suggests that a saliva test could be a simple, non-invasive way to identify people at risk of developing type 2 diabetes before symptoms appear.”

Type 2 diabetes affects about 400 million people worldwide and is diagnosed by high blood glucose levels. But Dr. Little notes that prediabetic conditions — such as insulin resistance and hyperinsulinemia — can develop 10 to 20 years before diagnosis.

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

Taking preventive measures early is important because hyperinsulinemia is a known predictor of several chronic diseases, including type 2 diabetes, hypertension, cardiovascular disease, stroke, cancer, and more recently, obesity.

Study co-author Dr Hossein Rafii explains that the aim of the study was to help develop a practical non-invasive test for hyperinsulinemia, but they also found an interesting result after taking the nutritional shake.

Previous research by Dr. Rafii at UBC Okanagan has shown that salivary insulin levels closely match plasma insulin levels throughout the day following consumption of mixed high- and low-carbohydrate meals.

"This suggests that salivary insulin may help distinguish high and low plasma responses to insulin and may 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 drink.

Dr. Rafii notes that, interestingly, some normal-weight participants also experienced sharp spikes in salivary insulin levels after taking the shake, suggesting that they may have an increased risk of type 2 diabetes, even without being overweight or having normal blood glucose levels.

"The finding that some thin people have high insulin is intriguing," says Dr. Rafii. "It suggests that salivary insulin may be more informative than body weight or waist circumference measurements."

The study also looked at the association between waist circumference, body mass index (BMI), age and gender and found that waist circumference had the strongest association with salivary insulin levels.

“These results suggest that waist circumference may be a more reliable indicator of hyperinsulinemia than age or total body weight when using salivary insulin,” he says. “Our results also suggest that salivary insulin may be better than blood glucose at discriminating between those who are more metabolically healthy and those who are more prone to hyperinsulinemia.”