Biphasic Dose Response in Low Level Light Therapy

TLDR

Low‑level light therapy (LLLT) has been used for over four decades to reduce pain, inflammation, and promote tissue healing, yet its mechanisms remain incompletely understood and its efficacy is controversial, partly due to a biphasic dose response described by the Arndt‑Schulz curve. This review aims to elucidate the molecular and cellular mechanisms of LLLT and present recent in vitro and in vivo findings that explain its biphasic dose response. The review analyzes molecular and cellular mechanisms of LLLT using in vitro and in vivo experiments to explain the biphasic dose response. Recent in vitro and in vivo studies reveal that specific light doses modulate mitochondrial activity and signaling pathways, accounting for the observed biphasic dose response.

Abstract

The use of low levels of visible or near infrared light for reducing pain, inflammation and edema, promoting healing of wounds, deeper tissues and nerves, and preventing cell death and tissue damage has been known for over forty years since the invention of lasers. Despite many reports of positive findings from experiments conducted in vitro, in animal models and in randomized controlled clinical trials, LLLT remains controversial in mainstream medicine. The biochemical mechanisms underlying the positive effects are incompletely understood, and the complexity of rationally choosing amongst a large number of illumination parameters such as wavelength, fluence, power density, pulse structure and treatment timing has led to the publication of a number of negative studies as well as many positive ones. A biphasic dose response has been frequently observed where low levels of light have a much better effect on stimulating and repairing tissues than higher levels of light. The so-called Arndt-Schulz curve is frequently used to describe this biphasic dose response. This review will cover the molecular and cellular mechanisms in LLLT, and describe some of our recent results in vitro and in vivo that provide scientific explanations for this biphasic dose response.