Lighting the way to non-invasive blood sugar levels

Diabetes is a very prevalent disease, but unfortunately there is still no cure. People with diabetes must regularly monitor their blood sugar levels (BGL) and take insulin to keep their blood sugar levels in check. In most cases, BGL measurements involve drawing blood from a fingertip using a finger prick. Because this procedure is painful, less invasive alternatives using modern electronic equipment are being actively researched around the world.

To date, several methods have been proposed to measure BGL. Those using infrared light are notable examples, and mid-infrared light-based devices have shown reasonable performance. However, the required light sources, detectors, and optical components are expensive and difficult to integrate into portable devices. In contrast, near-infrared light (NIR) is easily generated and detected using inexpensive components. Many smartphones and smartwatches already use NIR sensors to measure heart rate and blood oxygen levels. Unfortunately, glucose does not have a characteristic absorption peak in its NIR region, making it difficult to distinguish it from other chemicals in the blood, such as lipids and proteins.

To address this limitation, a research team led by Tomoya Nakazawa of Hamamatsu Photonics (Japan) recently developed a new methodology to estimate BGL from NIR measurements. Their research has the potential to revolutionize non-invasive blood sugar monitoring. Published in Biomedical Optics Journal.

The central contribution of this study is a new glycemic index that the research team derived from the basic NIR formula. Their approach begins with the extraction of oxyhemoglobin (HbO).₂) and deoxyhemoglobin (Hb) signals from NIR measurements. Through analysis of large amounts of data on NIR measurements, researchers realized that the cause was a phase lag (asynchrony) between the low-frequency and vibrational components of HbO.₂ Additionally, Hb signals are closely related to the extent of oxygen consumption during each cardiac cycle and therefore serve as metabolic indicators. “Although this phase delay-based metabolic index has not been reported by other researchers, it is a scientifically important discovery,” said Professor Nakazawa.

The team then sought to prove the relationship between this newly discovered metabolic index and BGL through a series of experiments. First, they used a commercially available smartwatch’s NIR sensor against the finger of a healthy, resting subject. The subjects then consumed a variety of sugar-sweetened and sugar-free beverages to induce changes in blood sugar levels. We conducted a similar experiment using a custom smartphone holder equipped with a high-brightness LED. The results were very encouraging, as the changes in the metabolic index closely matched the changes in blood sugar levels measured with a commercially available continuous blood glucose monitor. This confirms the phase delay between HbO.₂ And Hb is indeed closely correlated with BGL.

Clinical trials on diabetic patients are pending to confirm the applicability of the metabolic index in real-world situations. Still, researchers have high hopes for this innovative technology, as Nakazawa said: “The proposed method can, in principle, be implemented in existing smart devices with pulse oximetry capabilities and is inexpensive, battery-saving, and simple compared to other non-invasive methods.” Blood Glucose Monitoring Technology . Therefore, our approach could be a powerful tool towards portable and accessible BGL monitoring devices in the future. ”

We hope that these efforts will contribute to practical, non-invasive ways for diabetic patients to control BGL and thereby minimize the effects of the disease.

For more information, please see the original Gold Open Access article by Nakazawa et al.Non-invasive blood sugar estimation method based on phase delay between oxyhemoglobin and deoxyhemoglobin using visible/near-infrared spectroscopy,” J. Biomed.select. 29(3), 037001 (2024), doi 10.1117/1.JBO.29.3.037001.