Methane could be the first detectable indication of life beyond Earth

If life is abundant in the universe, atmospheric methane may be the first sign of life beyond Earth detectable by astronomers. Although nonbiological processes can generate methane, a new study by scientists at UC Santa Cruz establishes a set of circumstances in which a persuasive case could be made for biological activity as the source of methane in a rocky planet's atmosphere.

This is especially noteworthy because methane is one of the few potential signs of life, or "biosignatures," that could be readily detectable with the James Webb Space Telescope, which will begin observations later this year.

"Oxygen is often talked about as one of the best biosignatures, but it's probably going to be hard to detect with JWST," said Maggie Thompson, a graduate student in astronomy and astrophysics at UC Santa Cruz and lead author of the new study.

Despite some prior studies on methane biosignatures, there had not been an up-to-date, dedicated assessment of the planetary conditions needed for methane to be a good biosignature. "We wanted to provide a framework for interpreting observations, so if we see a rocky planet with methane, we know what other observations are needed for it to be a persuasive biosignature," Thompson said.

Published March 28 in Proceedings of the National Academy of Sciences, the study examines a variety of non-biological sources of methane and assesses their potential to maintain a methane-rich atmosphere. These include volcanoes; reactions in settings such as mid-ocean ridges, hydrothermal vents, and tectonic subduction zones; and comet or asteroid impacts.

The case for methane as a biosignature stems from its instability in the atmosphere. Because photochemical reactions destroy atmospheric methane, it must be steadily replenished to maintain high levels.

"If you detect a lot of methane on a rocky planet, you typically need a massive source to explain that," said coauthor Joshua Krissansen-Totton, a Sagan Fellow at UCSC. "We know biological activity creates large amounts of methane on Earth, and probably did on the early Earth as well because making methane is a fairly easy thing to do metabolically."

Nonbiological sources, however, would not be able to produce that much methane without also generating observable clues to its origins. Outgassing from volcanoes, for example, would add both methane and carbon monoxide to the atmosphere, while biological activity tends to readily consume carbon monoxide. The researchers found that nonbiological processes cannot easily produce habitable planet atmospheres rich in both methane and carbon dioxide and with little to no carbon monoxide.

The study emphasizes the need to consider the full planetary context in evaluating potential biosignatures. The researchers concluded that, for a rocky planet orbiting a sun-like star, atmospheric methane is more likely to be considered a strong indication of life if the atmosphere also has carbon dioxide, methane is more abundant than carbon monoxide, and extremely water-rich planetary compositions can be ruled out.

"One molecule is not going to give you the answer -- you have to take into account the planet's full context," Thompson said. "Methane is one piece of the puzzle, but to determine if there is life on a planet you have to consider its geochemistry, how it's interacting with its star, and the many processes that can affect a planet's atmosphere on geologic timescales."

The study considers a variety of possibilities for "false positives" and provides guidelines for assessing methane biosignatures.

"There are two things that could go wrong -- you could misinterpret something as a biosignature and get a false positive, or you could overlook something that's a real biosignature," Krissansen-Totton said. "With this paper, we wanted to develop a framework to help avoid both of those potential errors with methane."

He added that there is still a lot of work to be done to fully understand any future methane detections. "This study is focused on the most obvious false positives for methane as a biosignature," he said. "The atmospheres of rocky exoplanets are probably going to surprise us, and we will need to be cautious in our interpretations. Future work should try to anticipate and quantify more unusual mechanisms for nonbiological methane production."

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European earthworms reduce insect populations in North American forests

Earthworms introduced into northern North America have a negative impact on the insect fauna above ground. Soil ecologists found this impact for abundance as well as for biomass and species richness of insects. Their results indicate that changes in insect communities can have causes that have previously received little attention.

At least since the last ice age, about 10,000 years ago, there have been almost no earthworms in the northern part of North America. However, over the last few centuries, they have been introduced, probably through soil and plant transport from Europe. Since then, they have been dispersed and changed the soil significantly, with far-reaching consequences for the soil ecosystem. What impact these invaders have on the world above ground has, up to now, rarely been investigated.

The study was performed in a forest near Calgary in Canada, which has areas that are either inhabited or uninhabited by earthworms. Here, the researchers used insect vacuum samplers to capture aboveground insects and compared the catches. They discovered that the abundance, biomass, and species richness of insects in areas with invasive earthworms, and those areas without them differed significantly. Where earthworm biomass was highest, the number of insect individuals was reduced by 61 per cent, insect biomass by 27 per cent and species richness by 18 per cent.

Insect above ground affected by invasive earthworms underground

"We had expected that earthworms would have an impact on aboveground insects," says lead author Dr Malte Jochum from iDiv and Leipzig University. "Even so, I was surprised at how pronounced the effects were, and that not only the abundance but also biomass and species richness were affected."

The mechanisms by which the earthworms affect the insects are, however, still not clear. "It's possible that the earthworms eat the food and reduce the habitat of those aboveground insects, such as beetles and fly larvae, which break down dead plant material," says Jochum. Since the majority of insects are herbivores, it could also be hypothesised that the observed decline in insects is due to changes in the vegetation caused by altered soil conditions. In this case, however, the researchers were unable to detect any significant alteration in the number of plant species or plant coverage. "Still, this doesn't rule out the influence of the plants," says Jochum. However, the data on species composition and other functional characteristics of the plant communities have yet to be evaluated.

The increase in predatory insect species and spiders was also striking. These seem to be benefiting from the changes.

Underestimated causes for biodiversity loss to be considered in conservation

"Up to now, only a few causes have been used to explain global changes in insect populations; mostly alterations in habitats above the ground," says senior author Prof Nico Eisenhauer from iDiv and Leipzig University. "These new results show that biodiversity loss can also have other causes which have, so far, received little attention and that these should be taken into consideration when developing management and conservation strategies for biodiversity."

Introduced earthworm species are not only found in North America but on almost every continent. However, since there had been very few earthworms in northern North America for a very long time, the effect of these invaders is particularly pronounced. "For regions like Europe, where natural communities have always co-developed with earthworms, comparable negative effects due to new earthworm species are very unlikely," says Jochum. "Quite the opposite. Here they are important ecosystem engineers, which many important ecosystem functions depend on."

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Perseverance records the first ever sounds from Mars

NASA's Perseverance rover, which has been surveying the surface of Mars since February 2021, has for the first time recorded the acoustic environment of the Red Planet. An international team led by an academic at the University of Toulouse III -- Paul Sabatier and including scientists from the CNRS and ISAE-SUPAERO, carried out an analysis of these sounds, which were obtained using the SuperCam instrument built in France under the authority of the French space agency CNES. Their findings are published on 1st April 2022 in Nature.

For 50 years, interplanetary probes have returned thousands of striking images of the surface of Mars, but never a single sound. Now, NASA's Perseverance mission has put an end to this deafening silence by recording the first ever Martian sounds. The scientific team for the French-US SuperCam instrument installed on Perseverance was convinced that the study of the soundscape of Mars could advance our understanding of the planet. This scientific challenge led them to design a microphone dedicated to the exploration of Mars, at ISAE-SUPAERO in Toulouse, France.

Perseverance first recorded sounds from the Red Planet on February 19, 2021, the day after its arrival. These sounds fall within the human audible spectrum, between 20 Hz and 20 kHz. First of all, they reveal that Mars is quiet, in fact so quiet that on several occasions the scientists thought the microphone was no longer working. It is obvious that, apart from the wind, natural sound sources are rare.

In addition to this investigation, the scientists focused on the sounds generated by the rover itself, including the shock waves produced by the impact of the SuperCam laser on rocks, and flights by the Ingenuity helicopter. By studying the propagation on Mars of these sounds, whose behaviour is very well well understood on Earth, they were able to accurately characterise the acoustic properties of the Martian atmosphere.

The researchers show that the speed of sound is lower on Mars than on Earth: 240 m/s, as compared to 340 m/s on our planet. However, the most surprising thing is that it turns out that there are actually two speeds of sound on Mars, one for high-pitched sounds and one for low frequencies. Sound attenuation is greater on Mars than on Earth, especially for high frequencies, which, unlike low frequencies, are attenuated very quickly, even at short distances. All these various factors would make it difficult for two people standing only five metres apart to have a conversation. They are due to the composition of the Martian atmosphere (96% CO2, compared to 0.04% on Earth) and the very low atmospheric surface pressure (170 times lower than on Earth).

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Mammals put brawn before brains to survive post-dinosaur world

Prehistoric mammals bulked up, rather than develop bigger brains, to boost their survival chances once dinosaurs had become extinct, research suggests.

For the first 10 million years after dinosaurs died out, mammals prioritised boosting their body size to adapt to radical shifts in the make-up of Earth's animal kingdom, researchers say.

Their findings show that the size of mammals' brains, compared with their body weight, decreased following a catastrophic asteroid impact 66 million years ago that ended the reign of dinosaurs. It had been widely thought that mammals' relative brain sizes generally increased over time in the wake of the wipeout.

While much is known about the evolution of the brains of modern-day mammals, it has been -- until now -- unclear how they developed in the first few million years following the mass extinction.

A team from the University of Edinburgh has shed light on the mystery by performing CT scans on newly discovered fossils from the 10-million-year period after the extinction, called the Paleocene.

Their findings reveal that the relative brain sizes of mammals at first decreased because their body size increased at a much faster rate. Results of scans also suggest the animals relied heavily on their sense of smell, and that their vision and other senses were less well developed. This suggests it was initially more important to be big than highly intelligent in order to survive in the post-dinosaur era, the team says.

Around 10 million years later, early members of modern mammal groups such as primates began to develop larger brains and a more complex range of senses and motor skills. This would have improved their survival chances at a time when competition for resources was far greater, the team says.

The study, published in the journal Science, was supported by Marie Skłodowska-Curie Actions, European Research Council, Leverhulme Trust and National Science Foundation. It also involved New Mexico Museum of Natural History and Science in the US and several international institutions.

The idea that big brains are always better to invade new environments or survive extinctions is misleading, according to the research team.

Lead researcher Dr Ornella Bertrand, of the University of Edinburgh's School of GeoSciences, says: "Large brains are expensive to maintain and, if not necessary to acquire resources, would have probably been detrimental for the survival of early placental mammals in the chaos and upheaval after the asteroid impact."

Because today's mammals are so intelligent, it is easy to assume that big brains helped our ancestors outlast the dinosaurs and survive extinction -- but that was not so, the team says.

Senior author Professor Steve Brusatte, also based at the University of Edinburgh, says: "The mammals that usurped the dinosaurs were fairly dim-witted, and only millions of years later did many types of mammals develop bigger brains as they were competing with each other to form new ecosystems."

The badlands of northwestern New Mexico are among the few places where scientists can find complete skulls and skeletons of the mammals that lived immediately after the mass extinction of dinosaurs.

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Deserts 'breathe' water vapor, study shows

Deserts may seem lifeless and inert, but they are very much alive. Sand dunes, in particular, grow and move -- and according to a decades long research project, they also breathe humid air.

The findings show for the first time how water vapor penetrates powders and grains, and could have wide-ranging applications far beyond the desert -- in pharmaceutical research, agriculture and food processing, as well as planetary exploration.

The team's paper published in the Journal of Geophysical Research-Earth Surface.

Wanting to measure matter with greater sensitivity, lead author Michel Louge, professor of mechanical and aerospace engineering at Cornell University, developed a new form of instrumentation called capacitance probes, which use multiple sensors to record everything from solid concentration to velocity to water content, all with unprecedented spatial resolution.

In the early 2000s, Louge began collaborating with Ahmed Ould el-Moctar from University of Nantes, France, to use the probes to study the moisture content in sand dunes to better understand the process by which agricultural lands turn to desert -- an interest that has only become more urgent with the rise of global climate change.

The probe eventually revealed just how porous sand is, with a tiny amount of air seeping through it. Previous research hinted this type of seepage existed in sand dunes, but no one had been able to prove it until now.

"The wind flows over the dune and as a result creates imbalances in the local pressure, which literally forces air to go into the sand and out of the sand. So, the sand is breathing, like an organism breathes," Louge said.

That "breathing" is what allows microbes to persist deep inside hyper-arid sand dunes, despite the high temperature. For much of the last decade, Louge has been collaborating with Anthony Hay, associate professor of microbiology at Cornell, to study how microbes can help stabilize the dunes and prevent them from encroaching into roads and infrastructure.

Louge and his team also determined that desert surfaces exchange less moisture with the atmosphere than expected, and that water evaporation from individual sand grains behaves like a slow chemical reaction.

The bulk of their data was gathered in 2011, but it still took Louge and his collaborators another decade to make sense of some of the findings, such as identifying disturbances at the surface level that force evanescent, or nonlinear, waves of humidity to propagate downward through the dunes very quickly.

The researchers anticipate their probe will have a number of applications -- from studying the way soils imbibe or drain water in agriculture, to calibrating satellite observations over deserts, to exploring extraterrestrial environments that may hold trace amounts of water. That wouldn't be the first time Louge's research made its way into space.

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Researchers generate the first complete, gapless sequence of a human genome

Scientists have published the first complete, gapless sequence of a human genome, two decades after the Human Genome Project produced the first draft human genome sequence. According to researchers, having a complete, gap-free sequence of the roughly 3 billion bases (or "letters") in our DNA is critical for understanding the full spectrum of human genomic variation and for understanding the genetic contributions to certain diseases. The work was done by the Telomere to Telomere (T2T) consortium, which included leadership from researchers at the National Human Genome Research Institute (NHGRI), part of the National Institutes of Health; University of California, Santa Cruz; and University of Washington, Seattle. NHGRI was the primary funder of the study.

Analyses of the complete genome sequence will significantly add to our knowledge of chromosomes, including more accurate maps for five chromosome arms, which opens new lines of research. This helps answer basic biology questions about how chromosomes properly segregate and divide. The T2T consortium used the now-complete genome sequence as a reference to discover more than 2 million additional variants in the human genome. These studies provide more accurate information about the genomic variants within 622 medically relevant genes.

"Generating a truly complete human genome sequence represents an incredible scientific achievement, providing the first comprehensive view of our DNA blueprint," said Eric Green, M.D., Ph.D., director of NHGRI. "This foundational information will strengthen the many ongoing efforts to understand all the functional nuances of the human genome, which in turn will empower genetic studies of human disease."

The now-complete human genome sequence will be particularly valuable for studies that aim to establish comprehensive views of human genomic variation, or how people's DNA differs. Such insights are vital for understanding the genetic contributions to certain diseases and for using genome sequence as a routine part of clinical care in the future. Many research groups have already started using a pre-release version of the complete human genome sequence for their research.

The full sequencing builds upon the work of the Human Genome Project, which mapped about 92% of the genome, and research undertaken since then. Thousands of researchers have developed better laboratory tools, computational methods and strategic approaches to decipher the complex sequence. Six papers encompassing the completed sequence appear in Science, along with companion papers in several other journals.

That last 8% includes numerous genes and repetitive DNA and is comparable in size to an entire chromosome. Researchers generated the complete genome sequence using a special cell line that has two identical copies of each chromosome, unlike most human cells, which carry two slightly different copies. The researchers noted that most of the newly added DNA sequences were near the repetitive telomeres (long, trailing ends of each chromosome) and centromeres (dense middle sections of each chromosome).

"Ever since we had the first draft human genome sequence, determining the exact sequence of complex genomic regions has been challenging," said Evan Eichler, Ph.D., researcher at the University of Washington School of Medicine and T2T consortium co-chair. "I am thrilled that we got the job done. The complete blueprint is going to revolutionize the way we think about human genomic variation, disease and evolution."

The cost of sequencing a human genome using "short-read" technologies, which provide several hundred bases of DNA sequence at a time, is only a few hundred dollars, having fallen significantly since the end of the Human Genome Project. However, using these short-read methods alone still leaves some gaps in assembled genome sequences. The massive drop in DNA sequencing costs comes hand-in-hand with increased investments in new DNA sequencing technologies to generate longer DNA sequence reads without compromising the accuracy.

Over the past decade, two new DNA sequencing technologies emerged that produced much longer sequence reads. The Oxford Nanopore DNA sequencing method can read up to 1 million DNA letters in a single read with modest accuracy, while the PacBio HiFi DNA sequencing method can read about 20,000 letters with nearly perfect accuracy. Researchers in the T2T consortium used both DNA sequencing methods to generate the complete human genome sequence.

"Using long-read methods, we have made breakthroughs in our understanding of the most difficult, repeat-rich parts of the human genome," says Karen Miga, Ph.D., a co-chair of the T2T consortium whose research group at the University of California, Santa Cruz is funded by NHGRI. "This complete human genome sequence has already provided new insight into genome biology, and I look forward to the next decade of discoveries about these newly revealed regions."

According to consortium co-chair Adam Phillippy, Ph.D., whose research group at NHGRI led the finishing effort, sequencing a person's entire genome should get less expensive and more straightforward in the coming years.

"In the future, when someone has their genome sequenced, we will be able to identify all of the variants in their DNA and use that information to better guide their healthcare," Phillippy said. "Truly finishing the human genome sequence was like putting on a new pair of glasses. Now that we can clearly see everything, we are one step closer to understanding what it all means."

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When worlds collide: Studying impact craters to uncover the secrets of the solar system

While for humans the constants might be death and taxes, for planets the constants are gravity and collisions.

Brandon Johnson studies the latter, using information about impacts to understand the history and the composition of planets, moons, asteroids and meteorites throughout the solar system.

"Impact cratering is the most ubiquitous surface process shaping planetary bodies," Johnson said. "Craters are found on almost every solid body we've ever seen. They are a major driver of change in planetary bodies. They drive the evolution of planetary crusts. All the planets and asteroids were built from a series of impacts. Studying impacts can help us determine the composition and structure of planets."

As an associate professor in the Department of Earth, Atmospheric, and Planetary Sciences in Purdue University's College of Science, Johnson has studied almost every major planetary body in the solar system. And the time scale of his research ranges from relatively recent impacts to nearly the beginning of the solar system itself.

Collecting clues about collisions helps Johnson reconstruct the environment in which the collisions took place, offering deep insights into how and when bodies formed. His research is helping humans explore the planetary bodies in the solar system with only physics, math and a computer. Space missions and laboratory analyses provide a constant supply of new data and questions to work on.

"Most meteorites contain chondrules -- small, previously molten, particles," Johnson said. "Essentially, by studying the formation of chondrules by impacts, we can better understand what was going on in the nascent solar system. For example, based on one impact, we were able to determine that Jupiter had already formed right around 5 million years after the first solar system solids, changing the timeline of our understanding of the solar system."

Johnson and his lab staff incorporate known factors about the composition and physics of planetary bodies into complex computer models, running the models through a range of conditions and comparing the results with observed phenomena. Analyzing movements and collisions can offer insights into the composition of asteroids and meteorites, helping scientists understand how elements like water and metal are distributed through a solar system. By studying impact craters and basins on places like Pluto, Venus and icy moons, and the mechanics of other processes occurring on Europa and asteroids like Psyche, his team can understand more about their interiors; whether they have molten cores and plate tectonics, for example, or whether they have liquid oceans.

His work doesn't just span the solar system. He studies impacts closer to home, too, including on Earth's own moon and terrestrial impacts that may have affected the way Earth's crust, atmosphere and biosphere evolved.

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Where we grow up influences our sense of direction

The streets, alleys, paths and parks of our childhood leave a strong mark on us, with heretofore unsuspected benefits. A research team led by scientists from the Laboratoire d'Informatique en Image et Systèmes d'Information (LIRIS, CNRS/INSA Lyon/Université Claude Bernard Lyon 1) and the Institute of Behavioural Neurosciences at University College London has found that where people grow up influences their sense of direction in adulthood. From a diverse set of origins, from rural to cities of varying complexity, they had uneven skills in terms of orienting themselves.

First, the scientists have found that, on average, people who grew up in the countryside have a better sense of direction than people who grew up in cities. This extent of this difference varies from country to country: very strong in Canada, the United States, Argentina and Saudi Arabia, much less so in Austria, France, India and Vietnam.

The research team then looked at the maps of the major cities in these countries to categorize them according to layout complexity. While cities like Chicago are arranged in grids, with most branch lines at a right angle, cities like Paris form a more heterogeneous network, with nearly every angle present. Thus, according to their results, growing up in a city with a complex topography confers a better sense of direction.

The research also shows that people generally orient themselves better when confronted with topographies close to those travelled during childhood: they are better at navigating great distances if they come from rural areas, and better on a grid plan if they grew up in a city "with right angles."

These results were achieved with Sea Hero Quest, a video game developed to study Alzheimer's disease. After having memorized the game map, players are set objectives at several levels. It can be difficult to recruit participants to an experiment, and even more so to reproduce an experiment under identical conditions, and video gaming is a way to address these problems. For this study, from Sea Hero Quest we compared the sense of direction of nearly 400,000 people in 38 countries around the world.

From Science Daily

Flowers' unseen colors can help ensure pollination, survival

You can't see it, but different substances in the petals of flowers create a "bulls-eye" for pollinating insects, according to a Clemson University scientist whose research sheds light on chemical changes in flowers which helps them respond to environmental changes, including climate change, that might threaten their survival.

Matthew H. Koski, an assistant professor of biological sciences in the Clemson College of Science, led a research team that studied the bright, yellow flowers of Argentina anserina -- a member of the rose family commonly known as silverweed -- to learn how pigments in the petals that are visible only in the ultraviolet spectrum play an integral part in the plant's plasticity; that is, its ability to quickly respond to a changing environment. The team also included Clemson researchers Lindsay M. Finnell, Elizabeth Leonard and Nishanth Tharayil.

The journal Evolution featured the findings on the cover of its March edition.

The researchers studied silverweed growing at different elevations in southwestern Colorado to better understand the roles of the various UV-absorbing chemicals in the plants' petals and how these chemicals work to aid in pollination and, thus, reproduction.

Koski explained that although humans cannot see the UV patterns on the flower's petals, many of its pollinators can.

"I've always been fascinated with how [color variation of flowers] arises and how it evolves and what factors drive the evolution of color variation," Koski said, "so I got interested in thinking about how we perceive color versus how the organisms that interact more frequently with flowers perceive color."

"Insects -- pollinators, for example -- see in the ultraviolet spectrum," he continued. "So, flowers that reflect or absorb ultraviolet wavelengths give (to pollinators) the perception of different colors that we can't see. I've been fascinated with uncovering what these UV signals might be doing functionally with respect to pollination. When I thought about the trait of interest in ultraviolet absorption, it is biochemistry. It's a biochemical trait that leads to different perceptions of UV absorption and reflectance."

Koski said a wide range of plants have concentrations of UV-absorbing chemicals at the base of the flower's petals, while the tips of the petals have more UV-reflecting chemicals. He said this creates an overall "bulls-eye" effect that guides insects in their search for pollen.

The team wanted to uncover more about how the plants adapt to thrive in different environments -- in this case, a difference in altitude of 1,000 meters. They found that flowers at different altitudes adapt to their environments by producing differing amounts of UV-blocking or UV-absorbing chemicals.

"At higher elevations, there are always more UV-absorbing compounds or larger spatial area of UV absorption on the petals, compared to the low-elevation populations," Koski said.

The researchers said this demonstrates the plant's plasticity, which Koski defined as how differing traits arise in the same organisms under different environmental conditions. This is a critical step in understanding how organisms adapt to survive change.

"What's important about plasticity is, when we think about climate change and global change, plasticity is one mechanism by which natural populations can respond really rapidly to changing climates and persist under those climates," he said. "The process of evolution, where you're getting changes in the genetic code over time, is thought to proceed more slowly than just responding plastically to environmental change."

Koski said that one question raised by the research is whether plastic responses to environmental situations are adaptive. Do they offer any advantage to an organism, or are they changes in how a trait develops because of the environment without impacting plant fitness?

"One thing this study found is that the plastic change in UV pigmentation benefited the plant, especially the ones at high elevations because increases in ultraviolet absorption on the petals resulted in increased pollen viability," he explained.

Koski went on to say the research will help scientists better understand how organisms respond to environmental changes and even predict if or how well some organisms would be able to survive rapid environmental change, such as from global climate change. The research could also be important for agriculture, he said, because some of the same UV-sensitive pigments at work in silverweed are also present in commercial crops such as mustard and sunflowers.

"It's interesting to think about if abiotic factors like UV or temperature are shifting the expression of these traits, how is that going to impact how pollinators view the flowers, and how's that going to affect things like yield and seed production in crops, for example," Koski said.

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Good hydration may reduce long-term risks for heart failure

Staying well-hydrated may be associated with a reduced risk for developing heart failure, according to researchers at the National Institutes of Health. Their findings, which appear in the European Heart Journal, suggest that consuming sufficient amounts of fluids throughout life not only supports essential body functioning but may also reduce the risk of severe heart problems in the future.

Heart failure, a chronic condition that develops when the heart does not pump enough blood for the body's needs, affects more than 6.2 million Americans, a little more than 2% of the population. It is also more common among adults ages 65 and older.

"Similar to reducing salt intake, drinking enough water and staying hydrated are ways to support our hearts and may help reduce long-term risks for heart disease," said Natalia Dmitrieva, Ph.D., the lead study author and a researcher in the Laboratory of Cardiovascular Regenerative Medicine at the National Heart, Lung, and Blood Institute (NHLBI), part of NIH.

After conducting preclinical research that suggested connections between dehydration and cardiac fibrosis, a hardening of the heart muscles, Dmitrieva and researchers looked for similar associations in large-scale population studies. To start, they analyzed data from more than 15,000 adults, ages 45-66, who enrolled in the Atherosclerosis Risk in Communities (ARIC) study between 1987-1989 and shared information from medical visits over a 25-year period.

In selecting participants for their retrospective review, the scientists focused on those whose hydration levels were within a normal range and who did not have diabetes, obesity, or heart failure at the start of the study. Approximately 11,814 adults were included in the final analysis, and, of those, the researchers found 1,366 (11.56%) later developed heart failure.

To assess potential links with hydration, the team assessed the hydration status of the participants using several clinical measures. Looking at levels of serum sodium, which increases as the body's fluid levels decrease, was especially useful in helping to identify participants with an increased risk for developing heart failure. It also helped identify older adults with an increased risk for developing both heart failure and left ventricular hypertrophy, an enlargement and thickening of the heart.

For example, adults with serum sodium levels starting at 143 milliequivalents per liter (mEq/L) -- a normal range is 135-146 mEq/L -- in midlife had a 39% associated increased risk for developing heart failure compared to adults with lower levels. And for every 1 mEq/L increase in serum sodium within the normal range of 135-146 mEq/L, the likelihood of a participant developing heart failure increased by 5%.

In a cohort of about 5,000 adults ages 70-90, those with serum sodium levels of 142.5-143 mEq/L at middle age were 62% more likely to develop left ventricular hypertrophy. Serum sodium levels starting at 143 mEq/L correlated with a 102% increased risk for left ventricular hypertrophy and a 54% increased risk for heart failure.

Based on these data, the authors conclude serum sodium levels above 142 mEq/L in middle age are associated with increased risks for developing left ventricular hypertrophy and heart failure later in life.

A randomized, controlled trial will be necessary to confirm these preliminary findings, the researchers said. However, these early associations suggest good hydration may help prevent or slow the progression of changes within the heart that can lead to heart failure.

"Serum sodium and fluid intake can easily be assessed in clinical exams and help doctors identify patients who may benefit from learning about ways to stay hydrated," said Manfred Boehm, M.D., who leads the Laboratory of Cardiovascular Regenerative Medicine.

Fluids are essential for a range of bodily functions, including helping the heart pump blood efficiently, supporting blood vessel function, and orchestrating circulation. Yet many people take in far less than they need, the researchers said. While fluid guidelines vary based on the body's needs, the researchers recommended a daily fluid intake of 6-8 cups (1.5-2.1 liters) for women and 8-12 cups (2-3 liters) for men. The Centers for Disease Control and Prevention also provides tips to support healthy hydration.

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