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  • In a new paper, researchers found some evidence that light therapy may reduce certain dementia symptoms.
  • Behavioral and psychological symptoms of dementia include agitation, aggression, apathy, psychosis, repetitive questioning, wandering and other inappropriate behaviors.
  • The 12 studies in the meta-analysis included a total of 766 patients, with 426 who underwent light therapy. The rest served as controls for comparison.

Light therapy is often used by people with seasonal affective disorder (SAD) to improve their symptoms, but researchers are also exploring phototherapy as a non-invasive treatment for dementia.

In a new paper, published April 5 in the journal Brain and Behavior, researchers found evidence that light therapy may reduce certain dementia symptoms.

For the paper, researchers reviewed 12 previous randomized controlled trials (RCTs). They also combined the results of these studies, using a statistical method known as a meta-analysis.

“Our meta-analysis indicates that phototherapy improved cognitive function in patients with dementia but had no significant effect on [behavioral and psychological symptoms of dementia] and sleep,” the authors wrote.

Behavioral and psychological symptoms of dementia include agitation, aggression, apathy, psychosis, repetitive questioning, wandering, and other inappropriate behaviors.

“This suggests that phototherapy may be one of the most promising non-pharmacological interventions for improving core symptoms of dementia,” the authors continued.

The 12 studies in the meta-analysis included a total of 766 patients, with 426 who underwent light therapy. The rest served as controls for comparison.

Researchers found that light therapy was associated with improvement in cognitive function (thinking ability), as measured by the Mini-Mental State Examination.

However, no significant differences were seen between people who received light therapy and those who didn’t for depression, agitation or other dementia-related behavioral symptoms.

There was some indication that people who underwent light therapy had less severe agitation than controls, the study showed, but the difference between these groups was not statistically significant.

Researchers also found no difference between the groups for total sleep time, sleep efficiency — the percentage of time spent asleep while in bed — or symptoms of a sleep disorder.

Participants who underwent light therapy reported either no side effects or mild ones such as eye irritation and slight redness on the forehead. However, not all studies reported adverse effects.

One of the limitations of the meta-analysis is that it included a small number of studies and a small number of participants. The reason for this is that researchers focused on only the highest-quality studies that had been published at the time of their analysis.

In addition, the light therapy interventions varied across the 12 studies, which may explain some of the variability in the results of the individual studies.

For example, eight of the studies used bright light therapy, while two used LED light and two used blue or blue-green light.

The length of light therapy sessions ranged from 6 to 120 minutes, and from twice a day to five times per week.

In addition, about half of the studies exposed patients to light at specific times during the day — morning, afternoon or the dawn-dusk period. The rest did not specify a timing for the light, or they used a 24-hour lighting sequence.

Mariana Figueiro, PhD, said the variability in how these kinds of studies are carried out is one of the reasons we haven’t seen stronger results from light therapy for dementia.

“To me, this is probably one of the biggest issues with light therapy research,” said Figueiro, director of the Light and Health Research Center (LHRC) and professor of population health science and policy at the Icahn School of Medicine at Mount Sinai in New York City.

“But I think the effect is real,” she added. “I’ve seen studies where this is carefully done and you see the impact. Plus, there’s science behind it, a mechanism behind it.”

While the recent meta-analysis found benefits of light therapy for cognition in people with dementia, Figueiro said there is stronger evidence that it improves other areas.

“When the studies are done so that the light is actually delivered and received by the person, you see an improvement in sleep, and you see a reduction in depression,” she said.

In a study published in 2020 in the Journal of Alzheimer’s Disease Reports, Figueiro and her colleagues found that light therapy improved sleep at night and reduced depression and agitation in patients with dementia.

The new meta-analysis included an earlier study by Figueiro and her colleagues, which found similar improvements in sleep and mood.

As for the mechanism, Figueiro said the sleep-related effects seen with light therapy are due to the entrainment of the circadian rhythm — the alignment of the internal biological clock to external time cues such as the light-dark cycle.

These effects may spill over into other areas, including cognitive abilities.

“If you’re improving sleep, you’re likely to improve cognition,” said Figueiro, “because cognition is very much associated with sleep.”

While more research needs to be done to determine which type of light therapy intervention produces the strongest results, Figueiro said there are some general guidelines for how to deliver light effectively.

In general, the light reaching the eye should be brighter than what is found in the home, she said. In addition, the light should be delivered in a way that ensures the person receives the light, no matter which way they look.

People with seasonal affective disorder sometimes use a light box, which requires them to sit in front of the light and look in a certain direction. However, people with dementia may not be able to sit still long enough for the light to reach their eyes consistently.

“For Alzheimer’s patients, what you really want to have is more of a passive intervention, where you are illuminating the entire space where they spend their time,” said Figueiro.

This could be as simple as having people sit outside in the sunlight, or bringing more natural light into a room. If that isn’t possible, lamps can be placed close to where the person usually spends their time.

“This way, you guarantee that light is reaching the back of the eye, which is really the most important thing to be done for the circadian system,” said Figueiro.