The prevalence of mental health disorders has been rising over the years. According to the latest nationwide study, 1 in 7 people in Singapore has experienced a mental health disorder, which includes depressive and anxiety disorders[1]. In 2019, mental health disorders were one of the top four leading causes of disease burden in Singapore[2].

The research team thus set out to investigate the role microbes play in anxious behaviour. In pre-clinical studies, the scientists observed that in a germ-free environment, those which were not exposed to live microbes, showed significantly more anxiety-related behaviour than those with typical resident live microbes.

Further investigation revealed that the increased anxiety was associated with heightened activity in a brain region involved in processing emotions such as fear and anxiety, the basolateral amygdala (BLA). This was further identified to be related to specialised proteins within brain cells known as the calcium dependent SK2 channels, associated with anxiety behaviour. In conditions when the body and brain are exposed to live microbe metabolites, the SK2 channels act like a clutch, thus preventing neurons from becoming overly excited and firing too frequently.

Associate Professor Shawn Je from Duke-NUS’ Neuroscience and Behavioural Disorders Programme and one of the lead authors, explained:

“Our findings reveal the specific and intricate neural process that link microbes to mental health. Those without any live microbes showed higher levels of anxious behavior than those with live bacteria. Essentially, the lack of these microbes disrupted the way their brains functioned, particularly in areas that control fear and anxiety, leading to anxious behavior.”

To better understand the role of microbes in this process, the researchers introduced live microbes into germ-free mice[3]. This reduced the elevated neuronal activity in the basolateral amygdala and thus SK2 channel activity. As a result, the mice showed significantly less anxiety-related behavior — their emotional responses became like those exposed to microbes.

The researchers also tried treatment with indoles, microbial metabolites produced by certain microbes. When the germ-free mice were given indoles, they showed reduced activity in the basolateral amygdala and displayed less anxiety-related behaviour. This demonstrated that our indigenous microbes produce metabolites, which suggest a direct link between our microbiota and maintaining mental balance.

Professor Sven Pettersson from the Department of Research, National Neuroscience Institute of Singapore, who is also a lead author of the study, said:

“Establishing hunger signals and controlling hunger is an evolutionarily conserved defence mechanism. The physiological switch at birth, can therefore, be viewed as a first major wave of anxiety exposure for the newborn, which simply says, “If you don’t eat, you will die.” Additionally, birth is associated with exposure to breast milk, known to contain microbes that can produce molecules known as indoles. Indoles are known to be secreted in plants when they are exposed to stress or malnutrition (draught) and in this paper we report a similar mechanism in which indoles can regulate anxiety levels in mammals. That is, different levels of circulating microbial plasma indoles in the blood may reflect different sensitivity and vulnerability to stressful situations and therefore variable risk of experiencing anxiety-related situations.”

The implications of these observations are multiple: for example, it opens for the therapeutic potential of targeting the gut-brain axis to treat anxiety-related disorders by restoring the microbe composition through dietary supplementation with indoles or by introducing indole-producing gut microbes as probiotics. “In other words, it opens for tailor-made therapies in line with 21st-century precision medicine. Studies such as this illustrate the close hereditary relationship that exists between our indigenous microbes and the higher complexity of life,” concludes Pettersson.

Professor Patrick Tan, Senior Vice-Dean for Research at Duke-NUS, said:

“Our findings underscore the deep evolutionary links between microbes, nutrition and brain function. This has huge potential for people suffering from stress-related conditions, such as sleep disorders or those unable to tolerate standard psychiatric medications. It’s a reminder that mental health is not just in the brain-it’s in the gut too.”

The team now hopes to explore clinical trials to determine whether indole-based probiotics or supplements can be effectively used in humans as a natural anxiety treatment. If successful, this could mark the beginning of a new era in mental health care — one where gut microbes help keep our minds at ease.

[1] Institute of Mental Health, Singapore Mental Health study

[2] Ministry of Health 28 October 2020 Global Burden of Disease 2019 Study Findings https://www.moh.gov.sg/news-highlights/details/global-burden- of-disease-2019-study-findings

[3] The study was conducted according to the National Advisory Committee for Laboratory Animal Research (NACLAR) guidelines.

Biological age — a measure of how well one’s body is functioning — differs from chronological age — the amount of time since someone was born. While chronological age can be correlated to disease risk, researchers and medical doctors can use biological age, which can be slowed or accelerated by environmental or behavioral factors, to more precisely understand a person’s risk for certain diseases, including cancers and dementia.

The correct type of tissue is needed to estimate biological age accurately, according to the study led by Abner Apsley, doctoral candidate in the Penn State Molecular, Cellular, and Integrative Biosciences Graduate Program, and his adviser, Idan Shalev, associate professor of biobehavioral health at Penn State. Their results were published in Aging Cell.

In recent years, researchers created several epigenetic clocks — tools that compare a person’s biological age to their chronological age. As these clocks have become widely available, multiple companies have begun to offer services that estimate people’s biological age by comparing customer tissue samples to established epigenetic clocks.

Researchers construct epigenetic clocks by collecting tissue samples from a large number of people and examining differences in epigenetic markers — which indicate points of DNA methylation — across the lifespan. Using machine learning to identify which epigenetic markers predict chronological age, the researchers can then determine if a person’s epigenome, or the set of markers, matches their chronological age.

In theory, knowing a person’s biological age could indicate what behaviors that person needs to modify in order to extend their life. In clinical settings, however, scientifically validated uses of epigenetic clocks are not common yet, the researchers said.

“Aging is the main driver for a host of common diseases including dementia, heart disease and cancer,” Shalev said. “Measurement of biological age is not a diagnosis of a health problem, but it can be used to identify a person’s risk for age-related conditions.”

Some commercial companies offer to measure biological age by requiring customers to spit into a test tube and mail the sample to the company. The company analyzes epigenetic information in the saliva and uses established epigenetic clocks to predict the customer’s biological age. Epigenetic clocks, however, are most commonly created using blood, not saliva, which is why the researchers in this study said they wanted to compare the performance of different tissue-sample types.

The researchers evaluated five types of tissue samples and compared them with seven epigenetic clocks. The study included 284 distinct tissue samples from 83 individuals between the ages of nine and 70 years old. In six of the seven clocks tested, the team found that oral tissue resulted in substantially less accurate estimates of biological age than blood-based samples.

“We tested three types of blood samples and two types of oral tissues — saliva and cheek swabs,” said Apsley, the lead author of the study. “For almost every epigenetic clock, the oral tissue led to significantly higher estimates of the subject’s biological age. In some cases, the estimates were 30 years higher; that is extremely inaccurate. It is very clear that the tissue used to measure someone’s biological age must match the tissue used when the clock was created. Otherwise, estimates of biological age will not be valid.”

Results from this study demonstrated that blood-tissue types led to similar biological age estimates across the different epigenetic clocks. Oral tissue performed very differently than blood tissue and was generally not as accurate, estimating older biological ages across the clocks. The one exception to this trend was the only epigenetic clock in the study created using both blood and cheek swabs. For that clock, the age estimates across different tissues were much more accurate than they were on the other clocks.

“Most of the popular clocks were created using blood samples,” Apsley said. “So, these results represent an important lesson for this burgeoning field. If companies or physicians want to use saliva or cheek swabs to measure biological age, then researchers need to develop epigenetic clocks using those tissues. Currently, blood is needed to accurately estimate biological age in most circumstances.”

While tests of biological age are not commonly measured in medical settings yet, the researchers said that biological age could be used someday to identify patients who may need medication to delay the onset of an age-related disease due to their advanced biological age. Alternatively, patients with delayed biological age might be better candidates for surgery than other people of the same chronological age. There are other uses for biological age estimates, as well.

“Researchers are still discovering how to apply biological age,” said Shalev, a Social Science Research Institute co-funded faculty member. “Our research focuses on medical applications, but epigenetic clocks have also been used with blood samples from crime scenes to help forensic scientists identify the approximate age of criminal suspects. Who knows where this field will lead us next?”

Other researchers who contributed to this study include Qiaofeng Ye, Christopher Chiaro, John Kozlosky and Hannah Schreier of the Penn State Department of Biobehavioral Health; Avshalom Caspi, Laura Etzel-House and Karen Sugden of Duke University; Waylon Hastings of Texas A&M University; Christine Heim of the Berlin Institute of Health at Charite; and Jennie Noll and Chad Shenk of the University of Rochester.

The National Institute on Aging, National Institute of Environmental Health Sciences, National Institute of Child Health and Human Development, National Center for Advancing Translational Sciences and the Penn State College of Medicine funded this research.

The findings published today in the journal Science Advances suggests that the decline of global sulphur emissions as the result of clean air policies, coupled with the warming and fertilization effects of carbon dioxide emissions lifts a lid on wetland methane production resulting in increased emissions.

The resulting additional future release of 20-34 million tonnes of methane each year from natural wetlands would mean targets to reduce human-caused emissions need to be more stringent than currently set out in the Global Methane Pledge.

Methane, which is one of the most potent greenhouse gases in trapping heat in the atmosphere, is produced in wetlands around the world. Sulphur (in the form of sulphate) has a very specific effect in natural wetlands that reduces methane emissions, while CO₂ increases methane production by increasing growth in plants that make the food for methane-producing microbes.

Professor Vincent Gauci from the University of Birmingham and a senior author of the study said:

“Well-meaning policies aimed at reducing atmospheric sulphur appear to be having the unintended consequence of lifting this sulphur ‘lid’ on wetland methane production. This coupled with increased CO₂ means we have a double whammy effect that pushes emissions much higher.

“How has this happened? Put simply, sulphur provides the conditions for one set of bacteria to outmuscle another set of microbes that produce methane when they compete over the limited food available in wetlands. Under the conditions of acid rain sulphur pollution during the past century, this was enough to reduce wetland methane emissions by up to 8%.

“Now that clean air policies have been introduced, the unfortunate consequence of reducing sulphur deposition, which does have important and welcome effects for the world’s ecosystems, is that we will need to work much harder than we thought to stay within the safe climate limits set out in the Paris agreement.”

More than 150 nations signed up to the Global Methane Pledge at COP26 in Glasgow, which seeks to reduce human-caused emissions of methane by 30% on a 2020 baseline, by 2030.

The study is the latest to implicate reductions in atmospheric sulphur in driving warming at a faster rate than anticipated. In 2020 shipping pollution controls were introduced to reduce emissions of sulphur dioxide and fine particles that are harmful to human health. This reduction in atmospheric sulphur over the oceans has been implicated in larger warming that expected in what has come to be known as ‘termination shock’.

Lead author of the paper Lu Shen of Peking University said:

“Our study points to the complexity of the climate system. Representation of these complex biogeochemical interactions has not previously been well integrated into estimates of future methane emissions. We show that it is essential to consider these feedbacks to get a true understanding of the likely future of this important greenhouse gas.”

The two grains are critical for food security in India, the second most populous country in the world and home to a quarter of all undernourished people globally.

“We wanted to understand the impact of India’s coal electricity emissions on its agriculture because there might be real trade-offs between meeting growing electricity demand with coal generation and maintaining food security,” said Kirat Singh, a PhD student in environment and resources in the Doerr School of Sustainability and lead author of the Feb. 3 study in Proceedings of the National Academy of Sciences.

Clean air and food security

Past studies have sought to quantify overlooked costs of burning coal for electricity by estimating the number of deaths linked to resulting pollution. Government agencies and other organizations use these figures — and estimates of the economic value of statistical life — to understand the costs and benefits of various economic development strategies and environmental regulations.

Until now, however, estimates of crop damages specifically tied to coal-fired power stations — which supply more than 70% of electricity in India — have been lacking despite more than a decade of research showing that air pollutants such as ozone, sulfur dioxide, and nitrogen dioxide hurt crop yields.

“Crop productivity is incredibly important to India’s food security and economic prospects,” said senior study author David Lobell, the Benjamin M. Page Professor in the Doerr School of Sustainability’s Earth System Science Department. “We’ve known that improved air quality could help agriculture, but this study is the first to drill down to a specific sector and measure the potential benefits of reducing emissions.”

Crop damage concentrated in key regions and seasons

For the new study, the authors estimated rice and wheat crop losses linked to emissions of nitrogen dioxide, or NO₂, from coal power stations. They used a statistical model that combines daily records of wind direction and electricity generation at 144 power stations in India and satellite-measured nitrogen dioxide levels over cropland.

The authors found coal power plants affected NO₂ concentrations above cropland up to 100 kilometers, or roughly 62 miles, away. Eliminating coal emissions from all farmland within this range during key growing seasons (January-February and September-October) could boost the value of rice output across India by approximately $420 million per year and of wheat output by $400 million per year, according to the study.

“This study underscores the importance of looking at environmental issues under a systems lens,” said study co-author Inês Azevedo, a professor of energy science and engineering in the Doerr School of Sustainability. “Any policy focused on reducing emissions from coal power plants in India will be ignoring a crucial part of the problem if it does not consider the damages from air pollution to agriculture.”

In some states with high levels of coal-fired electricity generation, such as Chhattisgarh, coal emissions account for as much as 13-19% of the region’s nitrogen dioxide pollution, depending on the season. Elsewhere, like Uttar Pradesh, coal emissions contribute only about 3-5% of NO₂ pollution. Other common sources of the gas, which results from burning fossil fuels, include vehicle exhaust and industry.

Broad benefits from emission cuts

The analysis reveals that the value of lost crop output is almost always lower than the mortality damage caused by any given coal power station. But the intensity of crop damage per gigawatt-hour of electricity generated can often be higher. At 58 of the 144 power stations studied, rice damage per gigawatt-hour exceeded mortality damage. Wheat damage per gigawatt-hour exceeded mortality damage at 35 power stations.

“It’s rare to find a single thing — in this case, reducing coal emissions — that would help agriculture so quickly and so much,” said Lobell, who is also the Gloria and Richard Kushel Director of Stanford’s Center on Food Security and the Environment.

The researchers found little overlap among the stations associated with the largest crop losses and those associated with the highest mortality. This means benefits from possible emission reductions in the future could be more significant and widely distributed than previously understood. According to the authors, the results highlight “the importance of considering crop losses alongside health impacts when regulating coal electricity emissions in India.”

“Well-targeted policies to cut emissions could deliver thousands of dollars of increased crop output for each clean gigawatt-hour, in addition to all the climate and human health benefits,” said Singh.

Lobell is also the William Wrigley Senior Fellow at the Stanford Woods Institute for the Environment and a senior fellow at the Freeman Spogli Institute (FSI) and at the Stanford Institute for Economic Policy Research (SIEPR).

Azevedo is also a professor (by courtesy) of civil and environmental engineering, a joint department of the Doerr School of Sustainability and Stanford School of Engineering. She is also a senior fellow at the Stanford Woods Institute for the Environment and at the Precourt Institute for Energy.

“Some own the land for recreational purposes, some own it because they want to produce timber, and some are a combination of both. If one landowner controls invasive species but their neighbor does not for some reason, that could be problematic because the bioinvasion will spread over space and time,” said study author Shadi Atallah, associate professor in the Department of Agricultural and Consumer Economics, part of the College of Agricultural, Consumer and Environmental Sciences at Illinois.

Currently, conservation cost-share programs reimburse forest landowners for up to 75% of the cost of controlling invasive species. However, this is not necessarily the most efficient use of funds, Atallah noted.

“When you’re incentivizing someone to do something, you would like to know they weren’t going to do it without the incentive, or you have wasted your money. Would it make sense to change who qualifies for these payments in a way that optimizes the effect?”

Atallah employed game theory to explore these questions, using the example of glossy buckthorn in U.S. Eastern white pine forests. Glossy buckthorn is a fast-growing shrub that is exotic and invasive in North America. It can form a dense, persistent layer in forest understories, interfering with the growth of young pine trees and affecting wildlife habitat.

In a previous study, Atallah surveyed Maine and New Hampshire family forest landowners to understand how their willingness to control glossy buckthorn was motivated by the shrub’s effects on timber, trail recreation, and wildlife viewing. For the current study, he developed a theoretical modeling framework that estimated how each type of landowner would act and how their neighbor would respond, given various circumstances over a period of time.

“The model focuses on two cases: one is the recreationist, who likes to hike and enjoy the land, but they don’t like that the invasive shrub will block their path and interfere with wildlife viewing. The other is the timber producer, who gets a reduced amount of timber if the invasive shrub prevents white pine from growing to maturity,” he explained.

Atallah also considered the connectivity between forests and how the bioinvasion spreads to surrounding areas.

“Some invasive species are mostly spread by short distance dispersal, such as squirrels or other small mammals, while other species are spread through long-distance dispersal, such as birds and waterfowl, and the spread can be either fast or slow. Another factor is where the bioinvasion first appears and whether it makes sense to prioritize control at the starting point,” he said.

He found that in most scenarios, the recreationist would not control the invasive shrub without cost-share payment, while the timber owner would choose to control regardless of subsidies.

“Only in the case of fast long-distance dispersal does control get so expensive that nobody can do it without support. This is consistent with what we are currently doing; everybody qualifies for it. However, in all other cases — slow long-distance dispersal, and slow or fast short-distance dispersal — it would make sense to pay only the recreationists, who act as sources of bioinvasion spread when they refrain from control.”

Atallah noted that this may not seem fair; however, the timber landowners would still benefit even if only the recreationists are subsidized, because the spread is contained earlier and to a larger extent.

“We find the cost of control for the timber producers becomes lower once you have cleaned up the neighboring forestlands. Instead of partially reimbursing both types of landowners, the money could be used to cover 75% of control for the recreationist, and as a result, the timber owner would have less invasive species to deal with and control would be less expensive.”

The study provides one example of different landowner motivations, but this doesn’t mean the same dynamic always plays out, Atallah stated.

“My conclusion is that we should provide the subsidy to the weakest link, which is the entity that wouldn’t act otherwise and ends up acting as the source of the externality. In this case it’s the recreationist, but you could imagine a situation where it was the other way around. The model is adaptable to any given scenario,” he said.

“The idea is to consider any two different motivations to own the resource and how that could lead to different decisions in terms of controlling bioinvasion spread, and thinking about prioritizing those who would not control without subsidies.”