Prepared by Gabriel L. Schwartz, PhD, for Tobener Ravenscroft LLP
Housing and cognitive development are intimately linked, particularly during childhood and adolescence. This includes poor housing conditions, such as crowding, pest or mold infestations, physical dilapidation, inadequate heat or water, and toxic exposures such as lead or gas leaks. Broadly, children build cognitive skills best in safe, stable, engaging environments.1,2 Poor housing conditions can threaten children’s access to those environments by exacerbating household chaos, disrupting children’s routines, stressing and depressing parents, and directly impacting children’s physiological functioning.3,4 Researchers have thus investigated links between poor housing and cognitive impairment for decades.
Research on poor housing conditions and cognition falls into two categories. The first focuses on holistic assessments of poor housing quality. The second focuses on specific housing conditions or their sequelae. This document summarizes both groups of research as relevant to plaintiffs’ case.
Household chaos, disrupted routines, and physical dilapidation have high psychological and cognitive costs, inducing psychological stress. Chronic exposure to such severe stress has powerful effects on the body, altering parasympathetic nervous system function and dysregulating stress hormones such as cortisol.5 This phenomenon, known as “toxic stress,” can impair cognitive development, increase risk of depression and anxiety, and degrade physical health.6 Poor housing conditions are particularly pernicious because they affect everyone in the household. Ideally, parents would be able to provide emotional and material support to their children; this helps buffer chronic stress’ repercussions.7 But parents who are living in poor housing conditions are themselves psychologically burdened, impeding their ability to help their children overcome trying times. Indeed, studies show that poor housing conditions engender maternal depression and less responsive parenting.3,8-10
Research using holistic measures of poor housing quality has accordingly found—remarkably consistently—that living in poorer housing conditions is associated with poorer cognitive and socioemotional health. This is true even when statistically adjusting for an array of other social and economic factors and accounting for past cognitive skill performance (examining how housing conditions affect future cognition after accounting for past cognition). Cognitive deficits have been observed for executive functioning,11 rich measures of general intelligence (combining many areas of cognition into a single metric),12,13 reading and (among adolescents) math performance,3 task persistence,14 and socioemotional functioning.3,14,15 Additional studies show that living in crowded housing has a similar relationship to impaired cognitive development.22-24 While some of the studies in this literature are smaller studies of a few hundred youth, others leverage nationally representative datasets of tens of thousands of children and adolescents followed longitudinally. Further studies specifically demonstrate that the household chaos poor housing conditions engender 4 has cognitive consequences of its own.10,16-19
While these studies were not randomized control trials (RCTs)—the gold standard for determining causation—results are consistent across the existing literature. This is true despite the studies being conducted by different teams analyzing different longitudinal datasets, collected in different places, taking different approaches to accounting for confounders (variables that could cause both poor housing conditions and cognitive impairment, such as household poverty). This strengthens our confidence that the connection between cognition and poor housing conditions is not a random quirk of one team’s data but rather a robust, reproducible scientific consensus.
These applied studies are strengthened by findings from limited neurological research on brain architecture. In a study of Japanese adults that used MRI scans, inadequate heating and cooling was associated with worse brain connectivity and white matter organization (“factional anisotropy”),20 a marker of cognitive impairment.21 Though this clinical study had little confounding control, it offers compelling supporting evidence: it isn’t just that people living in poorer housing conditions have poorer cognition on cognitive tests. Their brains also exhibit physical signatures of cognitive impairment.
Indoor air pollution—including volatile organic compounds (VOCs) emitted by gas leaks, including those often experienced by tenants living in poorly maintained housing—has its own specific impacts on cognition. Exposure to VOCs drives oxidative stress in the body, leading to neuroinflammation, neuroendocrine system disruption, and cell death in the nervous system.25
Epidemiologic evidence for VOC exposure on cognition comes from a series of high-quality, though small, randomized control trials. This research has found VOCs impair participants’ ability to solve complex problems that require focus and attention;26 memory and concentration—both assessed via formal cognitive assessments and as self-reported by study participants;27 ability to learn—in particular, to improve on tests of short-term memory and concentration;28 and ability to maintain cognitive effort, hindering the speed with which people accomplish even rote cognitive tasks, such as typing.29 Exposure to low levels of tuolene, a gas found in trace amounts in natural gas, was also found in experiments to change the neurological function of parts of the brain responsible for memory.30 Even merely living in houses with gas appliances that can leak gas into indoor environments, as well as indoor nitrogen dioxide concentrations, is associated with worse inattention symptoms and poorer cognition in children.31
There are a small number of studies that have found no effect on cognitive performance from VOC exposure. However, these studies generally exposed participants to these compounds for short lengths of time 32 (much shorter than tenants experience when living in their house every day, and much shorter than the studies above) or did not have sufficient variation in cognitive scores to formally test for the effects of VOCs.33 One additional study showed VOC exposure did greatly increase reports of mental confusion but did not decrease cognitive testing scores, but the latter was likely the result of “practice effects.”34 (If you take a test multiple times, you tend to improve your score; participants took the test once without VOC exposure and then a second time shortly thereafter after being exposed to VOCs, meaning the effects of VOCs [harmful] and the effects of practicing [beneficial] may have canceled each other out.)
Dilapidated housing conditions—including insufficient heat, loud or stress-inducing mice or cockroach infestations, or crowded and loud housing with thin walls between apartments—can inhibit tenants’ ability to sleep. An overwhelming body of evidence accumulated over decades demonstrates that such poor, disrupted, and insufficient sleep has powerful effects on cognition and school performance.
Sleep is essential for cognitive function and development. Sleep is a critical time for memory consolidation, connection-building, and brain recovery.35,36 Without it, the brain struggles to retain new information or skills,37 with lower activation of the brain regions involved in attention, memory, executive function, and other higher-order cognitive tasks.38 Poor sleep is especially harmful during childhood and adolescence,39-43 when circadian rhythms and our homeostatic sleep-wake system (which regulates how much sleep we feel we need) shift to accommodate the needs of physical and neurocognitive maturation.40,44-46 Clinical studies demonstrate that poor sleep additionally disrupts activity in the portions of adolescent brains related to self-control and reward processing, leading to riskier decision-making.47 A lack of quality sleep is also linked to delayed white matter maturation during adolescence, a sign that poor sleep impairs neurocognitive development.39
Meta-analyses, which combine evidence from dozens of studies, show that poor sleep even for a short time impairs attention, working and short-term memory, processing speed of new information, problem-solving intelligence, and executive function, among other injuries.48,49 This includes randomized experiments among adolescents, which have found sleep deprivation to lower verbal skills, increase difficulty learning new abstract concepts, and impair short-term memory, problem-solving ability, and concentration.40,50-52 Chronically poor sleep, as experienced by plaintiffs, is especially deleterious. In a week-long experiment, chronic poor sleep yielded worse working memory, speed at solving math problems, and ability to stay alert, as well as corresponding changes in neurological function.53 Children who had more sleep problems in another longitudinal study showed substantially lower ability to learn verbal skills over three years, resulting in large cognitive deficits.54
Note: Though earlier studies in the first half of the 2000s were more mixed about the effects of sleep on cognition, subsequent meta-analytic, experimental, clinical, and longitudinal evidence is decisive.
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