An optical circuit detects PPG signals reflected from skin tissue at one or more different wavelengths. A processing circuit integrated in the biosensor or in communication with the biosensor identifies an insulin release event using the a first PPG signal at a first wavelength and second PPG signal at a second wavelength. A correlation function is performed on the first and second PPG signals during the insulin release. The correlation is used to determine a relative change in diameter of vessels during the insulin release event and determine vascular health in response to the relative change.
