On a cold winter's day, a ray of sunshine can bring warmth and healing. But did you know that the various colors of light contained in the sun's white light can not only illuminate the surface of our skin and treat skin diseases, but some can even penetrate deep tissues, such as the skull, to treat brain diseases?

Recently, scientists from the Zhejiang Oujiang Laboratory published a review article in an international journal, exploring the application methods and principles of phototherapy in various age-related diseases. Let's unveil the mysterious veil of this colorful world of phototherapy.

First, to understand phototherapy, we need to know the relationship between the penetration depth of light and its wavelength. In the electromagnetic spectrum, from ultraviolet light (UV) to visible light (including blue, green, red, etc.) and then to infrared light, the wavelength gradually increases, and the penetration depth also increases accordingly.

• Ultraviolet light has a wavelength range of 100-400nm and is mainly used to treat skin diseases such as psoriasis, atopic dermatitis, and vitiligo. Due to its short wavelength, it can only reach the surface of the skin.

• Blue light has a wavelength of 400-500nm and is used to treat superficial skin diseases such as acne and jaundice.

• Green light has a wavelength of 500-595nm and can treat pain and emotional disorders in addition to skin diseases.

• Red light (wavelength 625-740nm) and near-infrared light (wavelength 750-1100nm) have superior tissue penetration ability and can stimulate deep tissues, such as the brain, to treat brain diseases.

In phototherapy, not only the wavelength but also the irradiation frequency is very important. In transcranial phototherapy, pulsed light is significantly superior to continuous light because pulsed waves with frequencies closer to brainwave frequencies have advantages in improving brain injury and produce less heat, avoiding potential damage to the brain.

The thickness and anatomical location of the skull also affect the penetration effect of light. For example, the occipital region of the skull has higher transparency, allowing more light to penetrate. Scientists have also explored diverse phototherapy pathways, such as trans-ocular blue light phototherapy for seasonal affective disorder, and trans-nasal near-infrared light stimulation to regulate nervous system activity.

Why can phototherapy resist aging and treat diseases? This is mainly due to its activating effect on mitochondria. Mitochondria are the "energy factories" within cells. Phototherapy increases ATP synthesis by affecting the complexes of the mitochondrial electron transport chain, improving cellular energy production. At the same time, phototherapy can also reduce the production of peroxides after mitochondrial damage, reducing the occurrence of oxidative stress, a major culprit of aging.

Inflammation is also an important cause of aging and brain diseases. Studies have shown that phototherapy can significantly inhibit the expression of pro-inflammatory cytokines, regulate related signaling pathways, and reduce neuroinflammation and tissue apoptosis.

Phototherapy has shown unique charm in anti-aging. It can not only improve brain oxygen saturation and improve brain hypoxia but also increase the brain's utilization of nitric oxide and promote vasodilation. In addition, phototherapy can also multidimensionally enhance brain function by influencing the release of neurotransmitters and stimulating nerve growth factors. Phototherapy has shown its strong comprehensive ability, and with the development of more clinical research, we expect to see the application of phototherapy on a larger scale.

In general, phototherapy, as an emerging and promising therapeutic method, is gradually changing our understanding of anti-aging and disease treatment. Let us look forward to more research results on phototherapy in the future and jointly welcome a healthier and longer future.

References:

[1]Ding L , Gu Z , Chen H ,et al.Phototherapy for age-related brain diseases: Challenges, successes and future[J].Ageing Research Reviews, 2024:94.DOI:10.1016/j.arr.2024.102183.

[2]Lunova M ,Barbora Smolková, Uzhytchak M ,et al.Light-induced modulation of the mitochondrial respiratory chain activity: possibilities and limitations[J].Cellular and Molecular Life ences CMLS, 2019(2).DOI:10.1007/s00018-019-03321-z.

[3]Huang Z , Zhang Y , Ma X ,et al.Photobiomodulation attenuates oligodendrocyte dysfunction and prevents adverse neurological consequences in a rat model of early life adversity[J].Theranostics, 2023, 13(3).DOI:10.7150/thno.78777.

[4]Wang X , Li X , Zuo X ,et al.Photobiomodulation inhibits the activation of neurotoxic microglia and astrocytes by inhibiting Lcn2/JAK2-STAT3 crosstalk after spinal cord injury in male rats.[J].Journal of neuroinflammation, 2021, 18(1):256.DOI:10.1186/s12974-021-02312-x.