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Air Pollution Linked to Risk of 'Silent' Miscarriage
A typical adult takes around 20,000 breaths per day. If you live in a megacity like Beijing, with many of those lungfuls you're likely to inhale a noxious mixture of chemicals and pollutants.
According to BreatheLife, the air in the Chinese capital is 7.2 times above safe pollution levels, based on guidelines set out by the World Health Organization.
For expectant mothers, that means an increase in the risk of "silent" miscarriages, suggests a new large-scale study published in Nature Sustainability.
Air pollution is already known to raise the risk of premature birth, low birth weight and life-threatening health complications for pregnant women, like preeclampsia, which is marked by high blood pressure, or gestational hypertension.
But its impact on "silent" or missed miscarriages — where the fetus died or did not develop, but has not been physically miscarried — has been more difficult to establish.
A Toxic Link
A collaborative effort from 16 different authors at several universities in China, the study retrospectively examined the records of more than a quarter million pregnant women in Beijing from 2009 to 2017 in light of the womens' exposure to air pollution.
Among the women whose clinical records were studied, 17,497 — which is 6.8% — were found to have experienced these types of miscarriages.
The researchers found the probability of missed miscarriages increased with higher concentrations of air pollutants, taking into consideration different ages, occupations and air temperature.
Women who were older than 39 when they became pregnant, as well as farmers and blue-collar workers, had a higher risk of a missed miscarriage associated with air pollution, the authors said.
The authors defined "air pollution" as consisting of four pollutants: fine particulate matter (referred to as particulate matter 2.5 or PM 2.5), sulfur dioxide, ozone and carbon monoxide, and calculated the levels based on historic data from Beijing's network of air monitoring systems.
As the authors point out, previous research had found that when pregnant women are exposed to air pollution over the long-term, pollutants are able to cross the maternal-fetal blood barrier and affect the fetus.
Ultrafine and Ultratoxic
Most human-made air pollutants are extremely small: Particulate matter is about the diameter of a hair, and ultrafine particulate matter is even smaller. It's so tiny, in fact, it can travel from the lungs into our blood and circulate in the brain.
The myriad harmful health effects of air pollution are well known and range from respiratory illnesses and children's cognitive decline to infertility, polycystic ovary syndrome and dementia. Nearly one million children die every year from pneumonia and half of those deaths are linked to air pollution.
The Chinese study is not the first to have found a link between air pollution and miscarriages — in February 2019, a study conducted in Salt Lake City in the U.S., published in the journal Fertility and Sterility, found a increase of 20 micrograms of nitrogen dioxide per cubic meter was associated with a 16% rise in the risk of miscarriage.
That study analyzed the records of around 1,300 women between 2007 and 2015 who presented to the emergency department after having miscarriages. It found the strongest link between air pollution and lost pregnancy was the level of nitrogen dioxide in the seven days preceding a miscarriage.
Five years ago, the Chinese government declared a somewhat controversial "war on pollution," but air pollution levels in many cities around the country are still extremely toxic.
With global greenhouse gas emissions showing no sign of slowing down, China is not the only country with an air pollution problem. The World Health Organization says 91% of the world's population now lives in cities where the air is toxic.
The authors of the study noted that they will need to do more research to understand how air pollution affects the fetus, including modeling a wide range of environmental conditions using more data sources, particularly to include land use and land cover.
Reposted with permission from our media associate DW.
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By Ana Maldonado-Contreras
- Your gut is home to trillions of bacteria that are vital for keeping you healthy.
- Some of these microbes help to regulate the immune system.
- New research, which has not yet been peer-reviewed, shows the presence of certain bacteria in the gut may reveal which people are more vulnerable to a more severe case of COVID-19.
You may not know it, but you have an army of microbes living inside of you that are essential for fighting off threats, including the virus that causes COVID-19.
How Do Resident Bacteria Keep You Healthy?<p>Our immune defense is part of a complex biological response against harmful pathogens, such as viruses or bacteria. However, because our bodies are inhabited by trillions of mostly beneficial bacteria, virus and fungi, activation of our immune response is tightly regulated to distinguish between harmful and helpful microbes.</p><p>Our bacteria are spectacular companions diligently helping prime our immune system defenses to combat infections. A seminal study found that mice treated with antibiotics that eliminate bacteria in the gut exhibited an impaired immune response. These animals had low counts of virus-fighting white blood cells, weak antibody responses and poor production of a protein that is vital for <a href="https://doi.org/10.1073/pnas.1019378108" target="_blank">combating viral infection and modulating the immune response</a>.</p><p><a href="https://doi.org/10.1371/journal.pone.0184976" target="_blank" rel="noopener noreferrer">In another study</a>, mice were fed <em>Lactobacillus</em> bacteria, commonly used as probiotic in fermented food. These microbes reduced the severity of influenza infection. The <em>Lactobacillus</em>-treated mice did not lose weight and had only mild lung damage compared with untreated mice. Similarly, others have found that treatment of mice with <em>Lactobacillus</em> protects against different <a href="https://doi.org/10.1038/srep04638" target="_blank" rel="noopener noreferrer">subtypes of</a> <a href="https://doi.org/10.1038/s41598-017-17487-8" target="_blank" rel="noopener noreferrer">influenza</a> <a href="https://doi.org/10.1371/journal.ppat.1008072" target="_blank" rel="noopener noreferrer">virus</a> and human respiratory syncytial virus – the <a href="https://doi.org/10.1038/s41598-019-39602-7" target="_blank" rel="noopener noreferrer">major cause of viral bronchiolitis and pneumonia in children</a>.</p>
Chronic Disease and Microbes<p>Patients with chronic illnesses including Type 2 diabetes, obesity and cardiovascular disease exhibit a hyperactive immune system that fails to recognize a harmless stimulus and is linked to an altered gut microbiome.</p><p>In these chronic diseases, the gut microbiome lacks bacteria that activate <a href="https://doi.org/10.1126/science.1198469" target="_blank" rel="noopener noreferrer">immune cells</a> that block the response against harmless bacteria in our guts. Such alteration of the gut microbiome is also observed in <a href="https://doi.org/10.1073/pnas.1002601107" target="_blank" rel="noopener noreferrer">babies delivered by cesarean section</a>, individuals consuming a poor <a href="https://doi.org/10.1038/nature12820" target="_blank" rel="noopener noreferrer">diet</a> and the <a href="https://doi.org/10.1038/nature11053" target="_blank" rel="noopener noreferrer">elderly</a>.</p><p>In the U.S., 117 million individuals – about half the adult population – <a href="https://health.gov/our-work/food-nutrition/2015-2020-dietary-guidelines/guidelines/" target="_blank" rel="noopener noreferrer">suffer from Type 2 diabetes, obesity, cardiovascular disease or a combination of them</a>. That suggests that half of American adults carry a faulty microbiome army.</p><p>Research in my laboratory focuses on identifying gut bacteria that are critical for creating a balanced immune system, which fights life-threatening bacterial and viral infections, while tolerating the beneficial bacteria in and on us.</p><p>Given that diet affects the diversity of bacteria in the gut, <a href="https://www.umassmed.edu/nutrition/melody-trial-info/" target="_blank" rel="noopener noreferrer">my lab studies show how diet can be used</a> as a therapy for chronic diseases. Using different foods, people can shift their gut microbiome to one that boosts a healthy immune response.</p><p>A fraction of patients infected with SARS-CoV-2, the virus that causes COVID-19 disease, develop severe complications that require hospitalization in intensive care units. What do many of those patients have in common? <a href="https://www.cdc.gov/mmwr/volumes/69/wr/mm6912e2.htm" target="_blank" rel="noopener noreferrer">Old age</a> and chronic diet-related diseases like obesity, Type 2 diabetes and cardiovascular disease.</p><p><a href="http://doi.org/10.1016/j.jada.2008.12.019" target="_blank" rel="noopener noreferrer">Black and Latinx people are disproportionately affected by obesity, Type 2 diabetes and cardiovascular disease</a>, all of which are linked to poor nutrition. Thus, it is not a coincidence that <a href="https://www.cdc.gov/mmwr/volumes/69/wr/mm6933e1.htm" target="_blank" rel="noopener noreferrer">these groups have suffered more deaths from COVID-19</a> compared with whites. This is the case not only in the U.S. but also <a href="https://www.washingtonpost.com/world/europe/blacks-in-britain-are-four-times-as-likely-to-die-of-coronavirus-as-whites-data-show/2020/05/07/2dc76710-9067-11ea-9322-a29e75effc93_story.html" target="_blank" rel="noopener noreferrer">in Britain</a>.</p>
Discovering Microbes That Predict COVID-19 Severity<p>The COVID-19 pandemic has inspired me to shift my research and explore the role of the gut microbiome in the overly aggressive immune response against SARS-CoV-2 infection.</p><p>My colleagues and I have hypothesized that critically ill SARS-CoV-2 patients with conditions like obesity, Type 2 diabetes and cardiovascular disease exhibit an altered gut microbiome that aggravates <a href="https://theconversation.com/exercise-may-help-reduce-risk-of-deadly-covid-19-complication-ards-136922" target="_blank" rel="noopener noreferrer">acute respiratory distress syndrome</a>.</p><p>Acute respiratory distress syndrome, a life-threatening lung injury, in SARS-CoV-2 patients is thought to develop from a <a href="http://doi.org/10.1016/j.cytogfr.2020.05.003" target="_blank" rel="noopener noreferrer">fatal overreaction of the immune response</a> called a <a href="https://theconversation.com/blocking-the-deadly-cytokine-storm-is-a-vital-weapon-for-treating-covid-19-137690" target="_blank" rel="noopener noreferrer">cytokine storm</a> <a href="http://doi.org/10.1016/S2213-2600(20)30216-2" target="_blank" rel="noopener noreferrer">that causes an uncontrolled flood</a> <a href="http://doi.org/10.1016/S2213-2600(20)30216-2" target="_blank" rel="noopener noreferrer">of immune cells into the lungs</a>. In these patients, their own uncontrolled inflammatory immune response, rather than the virus itself, causes the <a href="http://doi.org/10.1007/s00134-020-05991-x" target="_blank" rel="noopener noreferrer">severe lung injury and multiorgan failures</a> that lead to death.</p><p>Several studies <a href="https://doi.org/10.1016/j.trsl.2020.08.004" target="_blank" rel="noopener noreferrer">described in one recent review</a> have identified an altered gut microbiome in patients with COVID-19. However, identification of specific bacteria within the microbiome that could predict COVID-19 severity is lacking.</p><p>To address this question, my colleagues and I recruited COVID-19 hospitalized patients with severe and moderate symptoms. We collected stool and saliva samples to determine whether bacteria within the gut and oral microbiome could predict COVID-19 severity. The identification of microbiome markers that can predict the clinical outcomes of COVID-19 disease is key to help prioritize patients needing urgent treatment.</p><p><a href="https://doi.org/10.1101/2021.01.05.20249061" target="_blank" rel="noopener noreferrer">We demonstrated</a>, in a paper which has not yet been peer reviewed, that the composition of the gut microbiome is the strongest predictor of COVID-19 severity compared to patient's clinical characteristics commonly used to do so. Specifically, we identified that the presence of a bacterium in the stool – called <em>Enterococcus faecalis</em>– was a robust predictor of COVID-19 severity. Not surprisingly, <em>Enterococcus faecalis</em> has been associated with <a href="https://doi.org/10.1053/j.gastro.2011.05.035" target="_blank" rel="noopener noreferrer">chronic</a> <a href="https://doi.org/10.1016/S0002-9440(10)61172-8" target="_blank" rel="noopener noreferrer">inflammation</a>.</p><p><em>Enterococcus faecalis</em> collected from feces can be grown outside of the body in clinical laboratories. Thus, an <em>E. faecalis</em> test might be a cost-effective, rapid and relatively easy way to identify patients who are likely to require more supportive care and therapeutic interventions to improve their chances of survival.</p><p>But it is not yet clear from our research what is the contribution of the altered microbiome in the immune response to SARS-CoV-2 infection. A recent study has shown that <a href="https://doi.org/10.1101/2020.12.11.416180" target="_blank" rel="noopener noreferrer">SARS-CoV-2 infection triggers an imbalance in immune cells</a> called <a href="https://doi.org/10.1111/imr.12170" target="_blank" rel="noopener noreferrer">T regulatory cells that are critical to immune balance</a>.</p><p>Bacteria from the gut microbiome are responsible for the <a href="https://doi.org/10.7554/eLife.30916.001" target="_blank" rel="noopener noreferrer">proper activation</a> <a href="https://doi.org/10.1126/science.1198469" target="_blank" rel="noopener noreferrer">of those T-regulatory</a> <a href="https://doi.org/10.1038/nri.2016.36" target="_blank" rel="noopener noreferrer">cells</a>. Thus, researchers like me need to take repeated patient stool, saliva and blood samples over a longer time frame to learn how the altered microbiome observed in COVID-19 patients can modulate COVID-19 disease severity, perhaps by altering the development of the T-regulatory cells.</p><p>As a Latina scientist investigating interactions between diet, microbiome and immunity, I must stress the importance of better policies to improve access to healthy foods, which lead to a healthier microbiome. It is also important to design culturally sensitive dietary interventions for Black and Latinx communities. While a good-quality diet might not prevent SARS-CoV-2 infection, it can treat the underlying conditions related to its severity.</p><p><em><a href="https://theconversation.com/profiles/ana-maldonado-contreras-1152969" target="_blank">Ana Maldonado-Contreras</a> is an assistant professor of Microbiology and Physiological Systems at the University of Massachusetts Medical School.</em></p><p><em>Disclosure statement: Ana Maldonado-Contreras receives funding from The Helmsley Charitable Trust and her work has been supported by the American Gastroenterological Association. She received The Charles A. King Trust Postdoctoral Research Fellowship. She is also member of the Diversity Committee of the American Gastroenterological Association.</em></p><p><em style="">Reposted with permission from <a href="https://theconversation.com/a-healthy-microbiome-builds-a-strong-immune-system-that-could-help-defeat-covid-19-145668" target="_blank" rel="noopener noreferrer" style="">The Conversation</a>. </em></p>
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