Research Spotlights: March 2022

Mental health emergency room visits and extreme heat among US adults

Recently published research supported by the NIEHS and the Wellcome Trust examined the association between extreme heat and emergency room visits for mental health concerns among adults residing in the U.S. Previous research has documented the links between extreme heat adverse physiological responses, such as heat rash and heat stroke, and some studies have identified links between extreme heat and mental health concerns. However, previous studies focused on the relationship between extreme heat and mental health have been limited by their focus on specific geographic regions or populations, and reliance on self-reported measures. In this study, researchers built upon previous work by examining claims data for individuals from across the U.S. with commercial or Medicare Advantage health insurance plans.

Using the OptumLabs Data Warehouse, researchers examined claims data for 3,496,762 emergency department (ED) visits among 2,243,395 unique individuals between the years of 2010 and 2019. These claims came from the most populous 2,775 counties in the U.S., where an estimated 97.6% of the population resides. Mental health diagnoses were identified by applying the Agency for Healthcare Research and Quality’s Clinical Classifications Software scheme to ICD-9 and ICD-10 principal diagnosis codes at discharge, including primary discharge diagnosis and secondary diagnoses. The research team utilized a case-crossover study design to estimate the association between daily maximum temperature and the incidence rate per county-day of ED visits with a diagnosis for any mental health condition as well as ED visits for specific mental health conditions (e.g., substance use disorder, schizophrenia, or mood disorders). They also examined differences in incidence rate ratios by age, sex, and geographic region within the U.S.

Overall, researchers found that higher warm-season temperatures were associated with higher rates of ED visits for any mental health condition. Furthermore, days of extreme heat were also associated with higher rates of ED visits for specific mental health conditions, including substance use disorders; anxiety, stress-related, and somatoform disorders; mood disorders; schizophrenia, schizotypal, and delusional disorders; self-harm; and childhood-onset behavioral disorders. The found greater incidence rate ratios for mental health-related ED visits among men compared with women. They also found increased incidence rate ratios were higher in the Northeast, Midwest, and Northwest, compared to other regions. They did not find any age-related differences.

According to the authors, this study did have a few limitations, including a lack of detailed information about the individuals included in the analysis due to the use of deidentified claim data, and the inclusion of claims for only those with commercial and Medicare Advantage health insurance plans, thus creating a sample skewed toward higher socioeconomic status.

In summary, this study provided a nationwide examination of the relationship between extreme heat on emergency department visits for mental health concerns. Researchers identified a potential increased risk for mental health-related emergency department visits on days with extreme heat, among adults residing in the U.S. The findings from this research have important implications for emergency preparedness during extreme heat, particularly for clinicians and healthcare staff that may be on the front lines for responding to mental health concerns.

Nori-Sarma A, Sun S, Sun Y, Spangler KR, Oblath R, Galea S, Gradus JL, Wellenius GA. Association Between Ambient Heat and Risk of Emergency Department Visits for Mental Health Among US Adults, 2010 to 2019. JAMA Psychiatry. 2022 Feb 23:e214369. doi: 10.1001/jamapsychiatry.2021.4369. Epub ahead of print. PMID: 35195664; PMCID: PMC8867392.

Your spouse’s education can positively affect your overall health

Education is correlated with positive health, however does your spouse's education also influence your health? The idea that the individual characteristics of one’s spouse may affect the partner’s health is considered a crossover effect–meaning that the effect of someone else’s conditions can cross over to impact the primary person of interest (and vice versa). A study supported by the NIA aims to address this question. It is unknown if the positive effect of spouse’s education being connected to better health is simply the result of marriage selection or of education attainment. In other words, if healthier people tended to have more schooling and to partner with those who also are highly educated, it would be more difficult to isolate a unique cross over effect.

To study a potential crossover effect of education within marriage, the researchers use data from The Wisconsin Longitudinal Study which cover over 50 years and follows both individuals, married couples, and siblings. To address the marital health selection issue, the researchers used a within-sibling-pair design that capitalizes on natural variation within pairs in spousal education to generate estimates of spousal crossover effects. This is used find pairs of people who were very similar across a variety of dimensions and then ask whether differences in their partners' education level could explain differences in their health.

The results showed that the effect of spousal education on a person's self-assessed overall health is positive and relatively large, suggesting that people benefit from having more highly educated partners. This positive relationship persisted after adjusting for an individual’s own education and a variety of other premarital characteristics, including cognitive ability and health and health behaviors prior to marriage. This pattern was especially pronounced among women, whose health was more closely tied to spousal education than men's. This may indicate the importance of education-related attainments, such as men being better positioned to convert their education into higher paying jobs and thus economic resources being health-promoting, Future studies are needed to further parse out this and other mediating effects.

Several limitations or future areas of research are suggested by the scientists. This study was limited to heterosexual couples due to the timing of the Wisconsin Longitudinal Study, which began in 1957, and it reflects the U.S. demographics of that era. Future studies will be needed to confirm these results with different population subgroups, birth cohorts, and other time frames in the life course. Additionally, marital selection seems to be getting stronger in recent years, meaning people are tending to increasingly marry across similar educational attainment levels. From a health equities perspective, it is yet to be determined what this means for future cohorts of individuals with of lower education who cannot or do not marry individuals with higher educational levels. In summary, this study highlights the importance of education as a public commodity worth investing in and suggests that its impact on overall public health may be quite large.

Halpern-Manners A, Hernandez EM, Wilbur TG. Crossover Effects of Education on Health within Married Couples. J Health Soc Behav. 2022 Jan 8:221465211063879. doi: 10.1177/00221465211063879. Epub ahead of print. PMID: 35001695.

Anxiety-like behaviors linked to molecules produced by gut bacteria in mice

Previous research has reported a correlation between complex emotional behaviors and changes in the gut bacteria in humans and in animal models, however little is known about this relationship. A recent study, supported by the NIGMS, NIMH, NIA, NSF, and others, sheds some light on this relationship using a mouse model. It has been known that there are communities of bacteria that inhabit the intestines of animals (the microbiome) that can influence physiology and function, including the immune system, and metabolism. More recently studies have linked the microbiome to brain function and mood (or mood-like states) in humans and animal models Additionally, individuals experiencing certain neurological conditions have different gut microbiomes. Manipulation of these bacterial communities has been shown in mouse models to alter neurodevelopmental and neurodegenerative states.

In the current study, researchers focused on a bacterial metabolite called 4-ethylphenyl sulfate (4EPS), which is found in mice and humans, and has been linked to alterations in neurodevelopment and behavior. The study included two groups of mice, one group’s gut was colonized with bacteria that were genetically engineered to produce 4EPS and the control were colonized with identical bacteria that except they lacked the ability to produce 4EPS. Then, the mice were introduced to a new, unfamiliar area (behavioral arena), and researchers measured each mouse's behavior. In mice, anxiety-like behaviors are measured by the mouse’s explorations of a new space as well as the time spent in an open, “risky,” environment.

They found that mice with 4EPS spent less time exploring the area and more time hiding as compared to the controls, indicating the 4EPS mice exhibited increased anxiety-like behaviors. To probe this further, the researchers performed brain scans of the mice and observed that the 4EPS mice had increased activation in certain brain areas that are associated with fear and anxiety, as well as overall differences in brain activity and functional connectivity. At a cellular level, they found that oligodendrocytes, brain cells that produce myelin, were altered. Additionally, 4EPS mice that received treatment with a drug that increases myelin production in oligodendrocytes exhibited normal myelin production and a reduction in anxiety-like behaviors.

In summary, this study found that a bacterial metabolite, produced by bacteria residing in the gut, can alter the function of brain cells, resulting in an increase in anxiety-like behaviors in mice. This adds to the current knowledge base regarding brain function in receiving and integrating sensory and molecular cues from the periphery, the environment, and even of molecules of microbial origin. These findings likely have implications for human neurological conditions, including anxiety and other mood disorders.

Needham BD, Funabashi M, Adame MD, Wang Z, Boktor JC, Haney J, Wu WL, Rabut C, Ladinsky MS, Hwang SJ, Guo Y, Zhu Q, Griffiths JA, Knight R, Bjorkman PJ, Shapiro MG, Geschwind DH, Holschneider DP, Fischbach MA, Mazmanian SK. A gut-derived metabolite alters brain activity and anxiety behaviour in mice. Nature. 2022 Feb;602(7898):647-653. doi: 10.1038/s41586-022-04396-8. Epub 2022 Feb 14. PMID: 35165440.