Saliva and Tears As Non-Invasive Tests for Metabolic Health
- Sep 2
- 2 min read
Updated: Sep 6
Medical science is constantly seeking less invasive methods to monitor health and detect chronic diseases. Recent studies have highlighted the potential of bodily fluids such as saliva and tears to replace, under certain conditions, traditional blood tests. This innovation could transform the way we diagnose and monitor conditions like diabetes and obesity.
A pilot study, published in the journal Physiologia, investigated the feasibility of saliva and tears as alternatives for measuring vitamin D and glucose levels in patients with type 2 diabetes and healthy adults. The findings suggest a strong positive correlation between blood and tear glucose levels, indicating that tear sampling could be a potentially reliable and non-invasive alternative approach for monitoring glucose levels in diabetic patients.
Regarding vitamin D, the study found a significant negative correlation between blood and salivary vitamin D levels in diabetic patients diagnosed for at least five years. Although saliva might reflect blood vitamin D levels under certain conditions, this capacity has not yet been established as a reliable matrix for vitamin D detection. The research also observed a tendency towards a non-significant negative correlation between vitamin D levels in blood and tears, with tears samples containing higher levels. It is important to note that previous findings in healthy volunteers showed a positive correlation, suggesting that health conditions may influence vitamin D levels in different biological samples.
On the other hand, research from the University of British Columbia Okanagan, published in Applied Physiology, Nutrition, and Metabolism, reveals that saliva insulin tests offer a non-invasive method to effectively predict the risks of type 2 diabetes and obesity. Researchers observed that people with obesity had significantly higher insulin levels in their saliva at all evaluated time points, compared to individuals with normal weight or overweight, even when their blood glucose levels were similar.
This study suggests that measuring saliva insulin could help identify hyperinsulinemia (elevated insulin levels) much earlier than when blood glucose levels begin to rise, allowing for early interventions such as lifestyle changes. Hyperinsulinemia is a known predictor of various chronic conditions, including type 2 diabetes, hypertension, cardiovascular disease, stroke, and certain cancers. Furthermore, a strong relationship was found between obesity markers, such as waist circumference and body mass index (BMI), and higher levels of insulin in saliva, suggesting that waist circumference could be a more reliable indicator of hyperinsulinemia than age or overall body weight. Specific cut-off values for saliva insulin have been proposed to identify hyperinsulinemia.
Both studies highlight the great potential of non-invasive tests for metabolic health monitoring, although they emphasize that these findings are preliminary and require large-scale studies to confirm the observed correlations and establish specific reference ranges for each biological fluid before clinical application. Factors such as protein content, pH, enzymatic activity, and viscosity of these matrices can affect analyte distribution and assay performance.
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