Scontri C.M.C.B. et al. - Photobiomodulation and glycemic control in type 2 diabetes

This randomized, double-blind, crossover trial, conducted in 10 patients with type 2 diabetes, reports a decrease in capillary blood glucose levels following muscular photobiomodulation, with a dose of 100 J per site proving to be the most effective. The sample size is very small, and among the treated patients, there was no difference in blood glucose levels between the 100 J group and the placebo group receiving medication.

What this study measured

In 2023, Clara Scontri and her colleagues published a randomized, crossover, double-blind trial against a sham treatment in the *Journal of Biophotonics*. Ten patients with type 2 diabetes were evaluated six times: three while taking their usual oral hypoglycemic medication, and three without it.

The protocol used 830 nm, 25 arrays of light-emitting diodes at 80 mW per array, and compared three doses per site: 0 J (sham), 100 J, and 240 J, applied bilaterally to the quadriceps, hamstrings, triceps surae, arms, and forearms. Capillary blood glucose was measured at fasting, one hour after a standardized 338-kcal meal, and then 30 minutes, 3 hours, 6 hours, and 12 hours after the session. Heart rate variability was used to assess autonomic control. The abstract does not mention any associated physical exercise: the light was applied to the muscles at rest.

Key Findings

The data in the summary are as follows.

• Without antidiabetic treatment: decrease in blood glucose levels after all doses
• 100 J per site: optimal dose, effect lasting up to 12 hours, lowest area under the curve
• With treatment: similar decline across dose levels
• No difference in blood glucose levels between the 100-day treatment alone and the sham procedure combined with the medication
• Area under the curve significantly lower after 100 J, interpreted as better glycemic control
• The low-frequency component of heart rate variability was increased after sham + medication and after 100 J, suggesting sympathetic activation

No absolute values, confidence intervals, or p-values are shown.

How Photobiomodulation Affects Metabolism

The proposed explanation remains hypothetical. Near-infrared light at 830 nm is thought to be absorbed by cytochrome c oxidase, the final complex in the mitochondrial respiratory chain, which could increase adenosine triphosphate production and mitochondrial function in muscle. Since muscle is the primary site of glucose uptake after a meal, irradiating large muscle groups follows this logic. A reduction in oxidative stress and low-grade inflammation is also suggested, although none of these markers have been measured.

Limits You Should Know

Ten patients: the sample size is very small. This is a single trial, not a meta-analysis, which precludes any generalizations, and the crossover design does not overcome the lack of statistical power. The most nuanced finding: among treated patients, blood glucose levels did not differ between the 100-day group and the sham treatment combined with medication; only the area under the curve distinguished the two conditions. Follow-up did not exceed 12 hours and provides no insight into long-term outcomes. Finally, the increase in the low-frequency component warrants caution rather than enthusiasm.

What This Means in Practice

These exploratory results do not alter any treatment regimen. Photobiomodulation is in no way a substitute for antidiabetic treatment, and treatment should never be reduced or discontinued based on such results: any changes must be made exclusively by a physician. This raises an important point to note: while blood glucose levels may decrease after exposure, combining this with hypoglycemic therapy requires careful self-monitoring of blood glucose in the hours that follow, particularly when taking insulin or sulfonylureas. Any use of this therapy must be reported to the healthcare team.

Frequently Asked Questions

What was the most effective dose in this study?

The dose is 100 J per site, not 240 J. The authors report that this dose produces the longest-lasting effect—up to 12 hours—and the lowest area under the glucose curve. This result illustrates the nonlinear dose-response relationship described in photobiomodulation.

Was photobiomodulation combined with physical exercise?

The abstract does not mention any exercise sessions: the light was applied directly to large muscle groups at rest. The observed effect is therefore not attributable to concomitant physical activity, unlike other studies that combined the two.

Can we infer from this that it has an effect on glycated hemoglobin?

No. Follow-up ended at 12 hours, and the study measured only capillary blood glucose levels. Glycated hemoglobin reflects blood glucose control over approximately three months and was not assessed in this study.

Reference

Scontri CMCB, de Castro Magalhães F, Damiani APM, Hamblin MR, Zamunér AR, Ferraresi C. Dose- and time-response effects of photobiomodulation therapy on glycemic control in patients with type 2 diabetes, with or without hypoglycemic medication: A randomized, crossover, double-blind, sham-controlled trial. Journal of Biophotonics, 2023;16(10):e202300083. PMID 37171054. DOI 10.1002/jbio.202300083. https://pubmed.ncbi.nlm.nih.gov/37171054/

This summary is provided for informational purposes only and does not constitute medical advice. Photobiomodulation is not a substitute for prescribed treatment. Consult a healthcare professional.