Alzheimer disease and related dementias (ADRD) are a major public health challenge. The number of Americans aged ≥65 years with Alzheimer disease was estimated to be 6.7 million in 2023 [1]. In 2023, total payments for health care, long-term care, and hospice services for people aged ≥65 years with dementia were estimated to be US $345 billion in the United States. The number of people with Alzheimer disease in the United States is projected to grow to 13.8 million by 2060 [1].

A major component of the high psychological and financial costs of ADRD is related to addressing the needs of people living with dementia who have behavioral and psychological symptoms of dementia (BPSD), also called neuropsychiatric symptoms. BPSD encompass the challenging behaviors exhibited by people living with dementia that comprise a variety of symptoms that commonly include, but are not limited to, apathy, anxiety, depression, agitation, delusions, hallucinations, motor disturbances, and sleep changes. These symptoms are associated with faster disease progression [2], increased caregiving burden [3], and earlier placement into long-term care settings [4]. Pharmacological intervention is often not effective and is associated with undesirable side effects [5], with nonpharmacological therapy being a first-line approach to management [6].

The causes of BPSD are multiple, ranging from intrinsic neuropathologic factors to human factors such as caregiver interactions and the social-environmental milieu [7]. There is considerable evidence suggesting that environmental factors can affect the progression of different diseases as well as human behaviors [8,9]. The environment as a risk factor for ADRD has been reviewed, suggesting links between increased risks of ADRD and factors such as poor air quality, environmental toxins, and occupation-related exposures [10,11]. However, what has been less clearly examined is the potential direct relationship between person- or residence-level experienced environmental factors and contemporaneous behavioral changes associated with ADRD. This is important because most older people and people living with dementia spend the majority of their time indoors [12].

There has long been debate regarding the definition of the environment [13]. For the purpose of this review, we are focusing on the ambient environment as defined by Harris et al [14]. Factors pertaining to the ambient environment, such as light, noise, temperature, and humidity, contribute to the visual, acoustic, and thermal comforts of the occupants and may be associated with their BPSD [15]; for example, inadequate light has been suggested to be a risk factor for sundowning syndrome (people with late-stage dementia exhibiting more agitated behaviors in the late afternoon and evening) because of the role of light in vision and its role in circadian rhythm modulation [16,17]. Therefore, designing an indoor environment that would address the needs of people living with dementia is paramount and may reduce their BPSD. A first step to creating an optimal indoor environment for people living with dementia with BPSD is to understand which environmental factors are related to BPSD and how they impact the symptoms.

Previous papers have reviewed the effect of the long-term care environment on physical activity levels [18], the achievement of therapeutic goals such as safety and socialization [19], and neuropsychiatric symptoms [20,21]. However, these reviews have primarily focused on the parameters of the built environment (eg, size and layout of spaces), interior design, and occupancy and staffing ratios, rather than aspects of the environmental quality that impact comfort, such as temperature and humidity, noise levels, and lighting. Comfort is especially important to consider for people living with dementia because BPSD represent an expression of discomfort, stress, and unmet needs when insight and communication become more difficult [22]. Nevertheless, anosognosia and aphasia also prevent the subjective measurement of comfort. Thus, it is necessary to understand the impact of various objective aspects of environmental quality that may improve comfort and, in turn, BPSD.

Accordingly, we conducted this scoping review to (1) examine how indoor environmental quality parameters pertaining to light, noise, temperature, and humidity are associated with BPSD and how controlling these parameters can help manage these symptoms and (2) identify the current state of knowledge on the relationship between indoor environmental quality parameters and BPSD, current gaps in the research, and potential future directions.

We followed the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) reporting guidelines for this scoping review. We conducted a scoping review because we aimed to (1) provide an overview of the broad literature examining the relationship between indoor environmental quality parameters and BPSD and (2) identify gaps and future directions.

The databases used were CINAHL, Embase, MEDLINE, and PsycINFO. A literature search strategy was crafted for each database that would retrieve records containing a combination of appropriate index terms and text words pertaining to the following concepts: dementia (dementia, Alzheimer disease, etc), environmental conditions (heat, temperature, light, humidity, etc), and BPSD (anxiety, depression, apathy, agitation, pacing, etc). The complete search strategies can be found in Multimedia Appendices 1-3. The original search was performed on October 7, 2020, and updated on April 21, 2022, and February 22, 2024. The inclusion and exclusion criteria are presented in Textbox 1.

Six reviewers (WMA-Y, CW, MN, LM, RH, and KW) completed the screening process, which consisted of two stages: (1) title and abstract screening and (2) full-text screening. First, the title and abstract of each paper were reviewed by 2 reviewers independently to examine whether the studies met the inclusion criteria. The reviewers then met iteratively to reconcile any differences in their decisions regarding whether a particular paper should be included. If the 2 reviewers could not come to an agreement, a third reviewer would help reach a decision. After title and abstract screening was completed, the included papers at this stage were retrieved for full-text screening, and the process was repeated after reading the papers in their entirety.

Six reviewers (WMA-Y, MN, ZB, LM, RH, and SG) extracted data from the included papers after the screening process was completed. A survey built in Qualtrics (Qualtrics International Inc) was created to assist this process. The survey listed questions covering study design, year of publication, the region and residential settings in which the research was conducted, sample size, demographics of the sample, which environmental conditions were assessed and how they were examined, and which BPSD were evaluated and how they were measured. Next, the papers were categorized by the examined environmental factor or factors: (1) light level, (2) noise level, (3) temperature or humidity, and (4) multiple indoor environmental quality parameters. If there were unified themes of BPSD examined in the articles (eg, agitation and mood-related symptoms), the study results of each theme would be synthesized by summarizing the counts of different study designs and providing a narrative summary [23]. All study data were also summarized into tables. In doing so, the current state of knowledge, gaps in research, and future directions were identified.

Institutional review board approval was not required for this scoping review because the research did not involve human participants.

A total of 3123 articles were identified in the search initiated on October 7, 2020. After excluding papers published before 2006 as well as duplicates, the titles and abstracts of 1887 articles were screened, after which 1707 (90.46%) articles were excluded, and 180 (9.54%) were retrieved for full-text screening. Ultimately, of these 180 articles, 26 (14.4%) were included. The search was updated on April 21, 2022, and on February 22, 2024, and 12 articles were added to the final pool; hence, 38 papers were included in this scoping review (Figure 1). Of the 38 papers, 8 (21%) were randomized controlled trials (RCTs), 14 (37%) were quasi-experiments, 5 (13%) were pretest-posttest studies, 6 (16%) were cross-sectional studies, 4 (11%) were case series, and 1 (3%) was a cohort study (refer to Table 1 for more information).

The following sections synthesize the findings of the included studies, categorized by the indoor environmental quality factor or factors examined (Table 2).

Of the 5 studies that examined the relationship between temperature or humidity and BPSD [24,25,34,40,59], 3 (60%) were cross-sectional studies [24,34,40], and 2 (40%) were case series [25,59]; furthermore, 3 (60%) were conducted in North America [24,25,34], 1 (20%) in Europe [40], and 1 (20%) in Oceania [59]. Of the 5 studies, 4 (80%) were conducted in nursing homes or assisted living units [24,34,40,59], while 1 (20%) was conducted in participants’ private home environments [25]. The median sample size in these studies was 69 (IQR 21-122; range 10-160) participants. The participants’ mean age ranged from 79.7 to 86.6 years.

The case series study by Tartarini et al [59] found that the level of agitation of participants with dementia in a nursing home facility increased significantly when the indoor average temperatures diverged from 22.6 °C. At the same time, the duration of exposure to high temperature (>22.6 °C) and low temperature (<22.6 °C) was linearly correlated with Cohen-Mansfield Agitation Inventory scores. In the cross-sectional studies by Algase et al [24] and Cohen-Mansfield [34], the authors suggested that there was not enough variation in the indoor temperature level or humidity level to identify a relationship with participants’ behaviors.

A total of 8 studies [24,25,31-34,40,43] examined multiple indoor environmental quality parameters (refer to Table 2 for the combination of parameters examined in each study). Of these 8 studies, 7 (88%) were conducted in North America [24,25,31-34,43], and 1 (12%) was conducted in Europe [40]; furthermore, 3 (38%) were quasi-experimental studies [31-33], 3 (38%) were cross-sectional studies [24,34,40], and 2 (25%) were case series [25,43]. While the indoor environmental quality parameters—light level and noise level—were measured in the quasi-experimental studies, they were not manipulated. The intervention used in the quasi-experimental studies involved 9 categories of stimuli not related to the indoor environmental quality parameters.

Of the 8 studies, 5 (62%) reported some associations between indoor environmental quality parameters and BPSD. One of the themes that these studies suggested was that both overstimulation and understimulation from indoor environmental quality parameters can worsen BPSD. Algase et al [24] reported that brighter light and more variations in sound levels were associated with wandering. The studies by Cohen-Mansfield et al [31,33] that examined the effect of the physical environment on pleasure, engagement, and mood had similar findings. It was found that in nursing homes, pleasure was most likely to be experienced by participants with dementia in environments with moderate noise levels [33]. In addition, attention and engagement duration in participants with dementia were higher when light was normal in comparison to a dark room, and their attention and attitude were significantly less positive when the lighting in the room was bright than when the lighting was normal [31]. In the same study, all indicators of engagement significantly favored a moderate level of noise over no noise or low noise levels, and engagement duration was significantly longer for a moderate level of noise compared to high and very high levels of noise.

The cross-sectional study by Garre-Olmo et al [40] measured the physical environment in multiple spaces within the nursing home and found that indoor environmental quality parameters (light, temperature, and noise) in individual living spaces in the nursing home were uniquely associated with participants’ quality of life, behaviors, and mood as measured with the Quality of Life in Late-Stage Dementia Scale; for example, the authors found that low lighting levels in the bedroom were associated with signs of negative affect, high temperature in the bedroom was associated with lower quality of life experienced by the participants, and high noise levels in the living room were associated with low levels of social interaction.

To examine the relationship between multiple environmental factors and agitation in persons with cognitive decline in their home environments, Bankole et al [25] installed environmental sensors in people’s homes that provided continuous data over a 30-day period; in addition, the participants with cognitive decline wore actigraphy devices that provided objective measures of their activity level continuously. Furthermore, 10 caregivers used smartwatches or tablets to report episodes of agitation experienced by the people with cognitive decline in real time, which enabled more direct analysis of the relationship between the behaviors and contemporaneous environmental conditions. Personalized neural networks were built for 6 dyads, which predicted episodes of agitation with light level as a predictor. These networks achieved F₁-score values, which are measures of predictive performance in binary classifications, ranging from 86.12% to 97.07%. F₁-score values can range from 0% to 100%, with a higher F₁-score indicating a better predictive performance. Regarding temperature, the study [25] found that temperature showed strong positive correlation with Teager energy scores from actigraphy device data, which are measures of the aggregate energy of movement [68] and were associated with the agitation exhibited by the people living with dementia.

Of the 8 studies, 3 (38%) failed to identify a link between multiple domains of environmental conditions and BPSD. Jao et al [43] studied the association between apathy in residents with dementia in long-term care facilities and the characteristics of care environments, which included light level, noise level, environmental ambience, crowding, staff familiarity, and environmental stimulation. The authors found that light and sound levels did not show statistically significant effects on apathy [43]. Cohen-Mansfield et al [32] found that lighting and background noise were not associated with levels of agitation in nursing home residents with dementia but that may be due to small variations in these factors. Similarly, Cohen-Mansfield [34] reported no association between noise and mood in people with dementia attending recreational groups.

As seen in Table 2, of the 38 included studies, 6 (16%) relied solely on self-report data for measuring the environment, 13 (34%) used only sensors, and 2 (5%) use both sensors and self-report data, while the environment was not measured but manipulated in 17 (45%) studies. For measurements of BPSD in people living with dementia, of the 38 studies, 36 (95%) used informant-report scales, such as the Neuropsychiatric Inventory Questionnaire; less than half of these studies (n=16, 44%) also used behavioral sensors such as actigraphy to provide objective data.

The definition of environment encompasses several major elements: physical environment (eg, light level, noise level, temperature, and humidity), social environment (eg, number of people in proximity), and built environment (eg, furnishings). The focus of this scoping review is on the effects of the indoor environmental quality parameters pertaining to light, noise, temperature, and humidity on BPSD. Given the fact that most older individuals, including people living with dementia, spend most of their time indoors, better understanding of how these physical indoor environmental quality parameters may affect behavioral health is critical. Overall, this review outlines preliminary evidence on the notable linkages between indoor environmental quality parameters and BPSD. Further research remains to be conducted in the field.

The evidence base suggests that light during the day is helpful in modulating circadian rhythm, as well as alleviating sleep disturbance and mood-related disorders. Overall, overstimulation and understimulation of environmental factors can lead to challenging behaviors in people living with dementia; for example, when the environment exhibits high levels or low levels of noise, people living with dementia may exhibit more challenging or disturbing behaviors [44,49]. Similarly, challenging behaviors may be associated with the ambient temperatures experienced by the people living with dementia because there was more agitation observed when the environment was either relatively too hot or too cold for the person living with dementia [59]. Such findings are consistent with the existing models that explain the causes of BPSD, including the unmet needs model [69] and the progressively lowered stress threshold model [70]. Ultimately, finding the proper balance of environmental factors for providing the most personal comfort and quality of life for people living with dementia and caregivers may help to minimize the occurrences of BPSD.

Light is the most researched indoor environmental quality parameter. Most studies on light therapy have shown that it improves sleep and mood in people living with dementia. However, the findings regarding its effect on agitation are conflicting and warrant further research.

The evidence base generally suggests that when noise levels exceed tolerable ranges, behavioral symptoms become more frequent and severe. Studies indicate that both the time duration of exposure to noise and the type of noise exposure could contribute to behavioral symptoms. Future research should explore these factors further.

Studies examining the effects of temperature or humidity on BPSD are largely observational. There exists a need to better understand how thermal comfort affects BPSD in people living with dementia, especially because there are studies suggesting that older adults may need a higher ambient temperature to attain thermal comfort compared to younger adults [71,72].

Environmental factors were often evaluated using self-reported data, which can be prone to biases. The lack of objective measurement of the environment makes measuring and linking the specific effects of the indoor environmental quality parameters on the behaviors of people living with dementia difficult. Of the 38 included studies, 30 (79%) focused on a single environmental factor, measured over relatively short periods of time, limiting the ability to examine more holistically how the environment affects BPSD. To some degree, this single-domain focus may reflect the complexity as well as the cost of deploying multiple sensor types in multiple indoor spaces. As technology advances, indoor environmental quality parameter sensors are expected to become more affordable and scalable.

Although most environmental exposure occurs indoors, studies need to consider in parallel the outdoor environment in terms of its effects on behavior, which is especially important for studies conducted in personal residences because people also spend time outdoors. Going forward, studies should adopt a more holistic approach by deploying sensors to objectively and longitudinally measure the total environment.

While environmental conditions can be objectively sensed and measured, very often, BPSD of the people living with dementia are either reported by the person affected by dementia or observed and interpreted as occurring by an external observer (usually a caregiver) present when the behavior occurs. In this scoping review, 36 (95%) of the 38 included studies relied on these self-reports or observer reports of BPSD. This type of reporting may contain subjective bias. In addition, a variety of scales have been used for assessing the occurrences of BPSD, which differ in their content, structure, and timing of recall. This likely adds to imprecision in comparing the results across multiple studies. More research is needed to examine how different scales for evaluating BPSD relate to each other and, in turn, to multiple environmental conditions. At the same time, whenever possible, the assessment of BPSD should be corroborated with unobtrusive technology such as actigraphy, which can provide objective data.

As evidenced by multiple studies in this review, the effect of the environment on people living with dementia may be dependent on age, sex, and cognitive state. In addition, manifestations of BPSD may be unique for each person living with dementia as well. Recent work by Iaboni et al [73] showed that the features from wearable multimodal sensors varied in their importance to their predictive models for agitation by both individual and behavior type. Finding the optimal environment for each person living with dementia will help support aging in place, which will improve their quality of life and lower the cost of health care. This may be best achieved by being able to examine the environment and behavior at the individual level with a goal of achieving person-centered assessments of well-being in their environment. The use of continuous multimodal sensing data and frequent self-report facilitates the ability to evaluate and analyze data at the individual or “n-of-1” level [73-75], supporting the principle that each individual is unique. Care providers need to know the unique environments, needs, and preferences of each person with dementia to provide the best care and minimize troubling BPSD. Future research should seek to build effective computational models that will incorporate multiple continuous data streams, both environmental and behavioral, that will predict the occurrences of BPSD so that proactive intervention can be implemented [25].

At a macro level, the findings of this review, although they are rudimentary, can help inform the design of long-term care facilities and residential homes for people living with dementia. Individual assessments of responses to environmental factors can be conducted upon admission; for example, large windows may be used in long-term care facilities to let in sunlight, and this should be supplemented by a dawn-dusk simulation system to address the excessive, or lack of, sunlight in different seasons to modulate residents’ sleep and circadian rhythm. In addition, the temperature in long-term care facilities and older adults’ homes should be kept at an optimal range that would maximize the comfort of residents. Moreover, quiet flooring and sound-absorbing panels may be used in the long-term care facilities to reduce the noise level; as evidenced by the studies in this review, overly stimulating or noisy environments can increase BPSD. These measures may increase the cost of building and sustaining these long-term care facilities because, for example, maintaining a narrow temperature range can place additional strain on heating, ventilation, and air-conditioning systems in these facilities and may not be energy efficient. However, if the long-term care facilities are more attuned to the needs of people living with dementia, it may result in a decrease in BPSD, improving the quality of life of the people living with dementia and the caregivers as well. This would reduce staff burnout and turnover, ultimately lowering health care costs. Implementing such measures on a broad societal level requires further cost-benefit analysis.

This scoping review has limitations. One of the limitations is that we included studies with heterogeneous designs (eg, observational or experimental), which made the synthesis of results difficult. However, 1 of the aims of this scoping review was to provide an overview of the current state of knowledge regarding the relationship between indoor environmental quality parameters and BPSD. As such, heterogeneous studies were included. Another limitation is that only articles published in English were included. Moreover, only a subset of indoor environmental factors (light level, noise level, temperature, and humidity) were included in this review, while there are other factors relating to BPSD as well, such as psychosocial and biological influences [76]. Notably, this review did not include indoor air quality, another environmental factor that increasingly can be assessed objectively in situ. Air quality has been associated with depression and anxiety in older adults based on spatiotemporal models [77]. A recent study suggested that total volatile organic compound level, among other indoor factors, was significantly correlated with specific areas where behavioral changes occurred in people with moderate to severe dementia in a nursing home [78]. This review only provides evidence for the relationship between a subset of the indoor environmental quality parameters and BPSD, but the relationship likely is best interpreted in a much larger context.

This review suggests that indoor environmental quality parameters pertaining to light level, noise level, temperature, and humidity may be associated with BPSD. An environment that maximizes the comfort of people living with dementia may decrease their BPSD. Most of the studies (34/38, 89%) in this scoping review pertained to the environmental factor light level, while relatively few studies (5/38, 13%-11/38, 29%) examined the relationship between the remaining indoor environmental quality parameters and BPSD. Among the included studies, there were conflicting findings in the relationship between bright light and agitation, which will need further research. A variety of subjective scales were used to assess the environment and BPSD, which makes synthesizing and comparing results across studies difficult. Going forward, as computational methods and objective sensing technology advance and become more affordable, the behaviors of people living with dementia and their environments should be measured holistically and objectively so that future nonpharmacological intervention can be evidence based.