Effects of violet light exposure on aging dogs: a pilot study

Aging in dogs is known to induce various physical and brain alterations similar to dementia in humans. Concurrently with the recent extension of canine life expectancy, these age-related changes have imposed growing burdens on both dogs and their owners, emerging as a significant social issue. However, no curative treatment has yet been established, and the current mainstay of management focuses on improving the quality of life through symptomatic therapies, such as environmental modifications and pharmacotherapy. This study focused on violet light, which has suggested efficacy against such age-related changes. We developed a novel violet light irradiation device and evaluated its efficacy and safety in elderly dogs as a pilot study. An intra-individual comparison using an ABA design was employed with geriatric dogs aged 14 to 16 years housed in a senior dog care facility (two of which discontinued midway). The study design consisted of a one-month violet light exposure phase preceded and followed by two-week non-exposure periods. Physical activity levels were measured using accelerometers and cognitive function was assessed using the DISHAA and CCDR. To evaluate the safety, general physical and ophthalmic examinations were conducted by veterinarians. As a result, no significant overall effect was found on activity levels (Daytime: x ² = 4.22, p = 0.12; Nighttime: x ² = 1.58, p = 0.45). Similarly, no significant overall effects were observed for either the DISHAA or the CCDR (DISHAA: x ² = 1.60, p = 0.45; CCDR: x ² = 1.56, p = 0.46). However, a trend toward cognitive improvement was observed in six out of seven dogs and an upward trend in activity levels-indicating physical function improvement-was noted in two out of seven dogs. Regarding safety, no overt clinical abnormalities associated with violet light irradiation were identified. This pilot study demonstrated no clear overall effect, though some individuals showed signs of improvement. Future research should consider large-scale trials controlling for various variables.