Environmental factor – May 2022: Extramural documents of the month

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Tropical cyclones linked to rising US deaths

Over the past three decades, tropical cyclones in the United States have been associated with higher death rates in the following months, according to a study funded by the NIEHS. This is the first study to assess cause-specific mortality risks from tropical cyclones in the entire US population.

The study included death data from US counties that experienced at least one tropical cyclone between 1988 and 2018, as well as data from the Social Vulnerability Index, which combines 15 factors that weaken a community’s ability to respond to a disaster, such as poverty and lack of access to transport. The researchers used a statistical model to calculate how death rates after tropical cyclones and hurricanes – a subset of the strongest tropical cyclones – changed compared to similar periods without those storms.

Residents of 1,206 counties experienced at least one tropical cyclone during the study. In the month following a cyclone, each additional cyclone day was associated with higher county-level mortality rates for multiple causes of death, including injury; infectious and parasitic diseases; respiratory diseases; cardiovascular illnesses; and neuropsychiatric disorders. For hurricanes, injury-related deaths increased 33.4% in the month the storm hit.

Among the study population, the authors observed higher overall mortality rates among those aged 65 or older, injury-related deaths among women compared to men, and in the most socially vulnerable counties.

According to the authors, the results of the study contribute to a better understanding of how cyclones can affect deaths, providing a basis for improving resilience to climate-related disasters and climate change.

Quote: Parks RM, Benavides J, Anderson GB, Nethery RC, Navas-Acien A, Dominici F, Ezzati M, Kioumourtzoglou MA. 2022. Association of tropical cyclones with county-level mortality in the United States. JAMA 327(10):946–955.

Solar lighting intervention reduces indoor air pollution in Uganda

A solar lighting intervention reduced exposure to fine particulate matter (PM2.5) and black carbon in rural Uganda, according to a NIEHS-funded study. The use of kerosene and other fuel-based lighting contributes to household air pollution in many resource-limited settings. This is the first randomized study to examine whether solar lighting replaces fuel-based options and reduces exposure to harmful substances.

The study included 80 adult women living in rural Uganda. Half of the randomly selected participants received a solar home lighting system at the start of the study. The other half received the system a year later, at the end of the study. The researchers used light and temperature sensors to record the use of fuel-based lighting sources and light bulbs powered by solar intervention. They also deployed stationary and personal samplers for 48-hour periods to measure air pollutants.

Among the intervention group, kerosene lamps were completely removed in 92% of households. The intervention also resulted in a 37% decrease in PM2.5 and a 91% decrease in black carbon exposures.

The researchers followed up the participants after 12 months, reporting that the kerosene lamp displacement and reductions in personal exposure were maintained. According to the authors, solar lighting presents an immediate opportunity to reduce personal exposure to indoor air pollutants and should be considered in future interventions.

Quote: Wallach ES, Lam NL, Nuwagira E, Muyanja D, Tayebwa M, Valeri L, Tsai AC, Vallarino J, Allen JG, Lai PS. 2022. Effect of a solar lighting intervention on fuel-based lighting use and household air pollution exposure in rural Uganda: a randomized controlled trial. Indoor air 32(2):e12986.

Midlife metal exposure linked to metabolic syndrome in women

Metal exposure in midlife may contribute to the development of metabolic syndrome (MetS) in women, according to a study funded by the NIEHS. Research shows that middle-aged women are at greater risk for MetS than younger women. Prevention of MetS later in life requires a better understanding of the risk factors involved.

The study included 947 women aged 45 to 56 who did not have MetS. The researchers assessed the associations of urinary metal concentrations with the incidence of MetS each year for 17 years. The incidence of MetS was defined by subjects having at least three of the five components: arterial hypertension; higher than normal fasting blood sugar; abdominal obesity; high triglyceride levels; and low levels of high-density lipoprotein cholesterol, or “good” cholesterol.

Fifteen metals were detected in almost all of the participants’ urine samples. Higher concentrations of arsenic, cobalt and zinc were significantly associated with an elevated incidence of MetS over the study period. These associations persisted after controlling for demographic, socioeconomic, and lifestyle factors; menopausal status; and body mass index. Exposure to mixtures of multiple metals was also associated with a higher incidence of MetS.

According to the authors, metals could contribute to the development of MetS. They note that further studies are needed to confirm these findings and to investigate the underlying biological mechanisms.

Quote: Wang X, Karvonen-Gutierrez CA, Herman WH, Mukherjee B, Park SK. 2022. Metals and risk of incident metabolic syndrome in a prospective cohort of middle-aged women in the United States. Approximately Res 210:112976.

Link between placenta and fetal brain may predict neurodevelopmental disorders

A new NIEHS-funded study in mice showed that prenatal exposure to polychlorinated biphenyls (PCBs) altered DNA methylation in the placenta and fetal brain in ways consistent with neurodevelopmental disorders. DNA methylation is a molecular mechanism that regulates gene function and expression.

The placenta is responsible for eliminating toxic substances to protect the developing fetus, but PCBs can cross the placental barrier. The team aimed to determine whether changes in the placenta could serve as a predictor of DNA methylation in the brain.

Researchers exposed mice to PCBs through the diet before conception and during pregnancy and assessed effects on DNA methylation. They observed altered DNA methylation in thousands of regions – called differentially methylated regions (DMRs) – in the placenta and fetal brain of mice exposed to PCBs compared to controls.

The PCB-associated DMRs in placenta and brain overlapped significantly and harbored a shared subset of genes that control pathways important in cell differentiation and neuron growth. The researchers observed that these regions had an overrepresentation of genes previously associated with neurodevelopmental and autism spectrum disorders in humans.

According to the authors, placental DNA methylation profiles with measured exposures to PCBs could serve as predictive biomarkers to enable early intervention of PCB-associated neurodevelopmental disorders.

Quote: Laufer BI, Neier K, Valenzuela AE, Yasui DH, Schmidt RJ, Lein PJ, LaSalle JM. 2022. Placenta and fetal brain share a DNA methylation profile of neurodevelopmental disorder in a mouse model of prenatal PCB exposure. Cell Rep 38(9):110442.

(Mali Velasco is a research and communications specialist for MDB Inc., a contractor to the NIEHS Division of Extramural Research and Training.)

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