Depression is one of the most common symptoms affecting people living with Alzheimer's and other forms of dementia, occurring in 20 to 30 percent of patients. Despite depression's serious impact on well-being and quality of life for this population, doctors have few effective medical treatment options. And drug treatments can have serious side effects.

Increased access to daylight indoors, however, could provide caregivers with an effective and safe nonpharmacological option, according to research conducted by a USC professor of Architecture and a USC professor of gerontology, biological sciences and medicine, with assistance from an SC CTSI biostatistician. Their 12-week study, conducted with participants from eight dementia care communities in Los Angeles and Orange Counties, suggested that increasing exposure to daylight indoors could reduce depression in people living with dementia.

Kyle Konis, AIA, PhD

Research has already established the importance of regular exposure to sufficient light for maintaining healthy circadian entrainment, in both people living with dementia and those with normal cognitive function, explained principal investigator Kyle Konis, AIA, Ph.D., assistant professor of architecture at USC. 

Light exposure is a particular concern for those living in dementia care communities. "Light levels in institutionalized settings are often adequate for human visual lighting needs, but may lack the appropriate spectrum and intensity to effectively meet biological lighting needs,” said Konis.

The notion that bright light exposure can reduce depression symptoms is not novel, but existing light therapy studies typically involve attended use of specialized electrical lighting devices (for example, light boxes placed 1m from the eye) rather than on the lighting environment of physical spaces themselves; such studies offer little actionable evidence to support the design of indoor lighting environments that routinely improve the quality of care.

Developing evidence-based guidelines for daylight access.

There are currently no evidence-based guidelines for daylight access in dementia care communities, or senior housing in general, said Konis. “Yet, the utilization of daylight as the primary light source for human non-visual lighting needs is attractive for a number of reasons," he said. "Over millennia, light from the sun and sky served as a reliable indicator of time of day, and the peak Spectral Power Distribution (SPD) of daylight aligns closely with the peak sensitivity of the human circadian response. And, daylight from windows can achieve orders-of-magnitude higher levels of intensity compared with the light output from conventional electrical lighting systems.”

Guidance that can be used to orchestrate the appropriate timing, intensity, duration, and spectrum of light is important not just for physicians and caregivers seeking to use light therapies to help dementia patients, but also for architects and engineers seeking to design healthier built environments for everyone.

"Many designers already understand the importance of daylight access in buildings. However, we need to create a body of evidence to inform the development of metrics and design tools to effectively share and operationalize knowledge across the discipline to impact health," said Konis, who works at the intersection of building design, performance evaluation, and health. "We're dealing with access to biologically meaningful light in buildings, which is an important new performance issue that concerns nearly all indoor environments, not just memory care and senior living communities."

Although the potential of the research is exciting, the researchers acknowledge that they are at an early stage, and results are being used primarily as a basis to develop a larger, more informative trial.

Study collaboration with caregivers.

Among the pilot study's goals was to establish an effective “in-situ” method of measuring the full spectral power distribution of light exposure at eye-level at various locations within a space, as well as to develop an effective collaboration with caregivers at the memory-care communities involved in the research, run by Silverado Senior Living.

Konis conducted the pilot with Edward L. Schneider, M.D., Professor of Gerontology, Leonard Davis School of Gerontology and Professor of Biological Sciences Dornsife College of Letters, Arts and Sciences and Professor of Medicine Keck School of Medicine. SC CTSI biostatistician Wendy Mack, Ph.D., also assisted in study design and analysis and co-authored. Their findings were published in 2018 in the journal Clinical Interventions in Aging.

The study of light exposure and health relates in part to a category of visual receptors in the mammalian eye called intrinsically photosensitive retinal ganglion cells (ipRGC), said Konis. Unlike the retina's better-known and much more numerous rods and cones, ipRGCs aren't involved in image perception. Instead, they measure ambient light, which the brain uses to synchronize its circadian clock. Humans evolved as diurnal creatures, active during the day and sleeping at night; disruption of this routine, and of the associated exposure to daylight, can be unhealthy.

A bright light stimulus in the morning is the most powerful timing cue to maintain entrainment with the astronomical 24-hour day, said Konis. If made a priority during design, daylight from windows can provide a practical and low-cost option for providing this cue.

"While this outcome should be interpreted with caution due to the small number of study suggests that increased light exposure has the potential to be an effective treatment for residents with probable major depression, producing a reduction in symptoms similar to the reduction that would be expected with an effective pharmacological treatment," the study's authors wrote.

Based on the results of the pilot, the investigators' proposal for a new study on the topic is being considered for funding by the Robert Wood Johnson Foundation's Evidence for Action program.

NIH Funding Acknowledgment: Important - All publications resulting from the utilization of SC CTSI resources are required to credit the SC CTSI grant by including the NIH funding acknowledgment and must comply with the NIH Public Access Policy.