A new study in the Journal of Cosmology and Astroparticle Physics (JCAP) examined what would happen if dark matter experienced an additional attractive force. The results were surprisingly counterintuitive. Although the force causes dark matter to gather more efficiently, it usually does not accelerate the growth of cosmic structure. Instead, it tends to slow that growth.

Why Scientists Are Considering a Dark Force

Interest in a possible “dark force” has increased as highly precise observations of the Universe have produced results that do not always align perfectly.

Measurements of cosmic expansion and the development of galaxies and other large structures sometimes appear to tell slightly different stories. Some observations of the distant Universe suggest that expansion may have proceeded somewhat more slowly in the past than the standard cosmological model predicts.

At the same time, studies of the cosmic microwave background have long suggested that matter could be more tightly clustered across the largest scales of the Universe than expected.

These differences are relatively small, but they have encouraged scientists to ask whether the standard model of cosmology may be missing an important ingredient.

One possibility is that dark matter particles feel an extra force that ordinary matter cannot detect. Because the interaction would operate only within the dark matter sector, researchers refer to it as a “dark force.” Such an interaction could potentially affect both the Universe’s expansion and the formation of galaxies and larger cosmic structures.

“What we really know about dark matter has so far been learned only through its gravitational effects,” says Zachary Weiner, a researcher at the Perimeter Institute for Theoretical Physics, corresponding author for the study. “That leaves open the possibility that dark matter might have additional interactions that are hidden from ordinary matter.”

Testing a Force Beyond Gravity

The research team investigated a group of theoretical models in which dark matter particles interact through a long-range force in addition to gravity.

Using theoretical calculations together with cosmological data, the scientists studied how this hidden interaction would influence the history of cosmic expansion and the growth of large-scale structure.

At first, the expected result seems straightforward. If dark matter particles attract each other through another force, they should assemble into clumps more quickly. That stronger clustering might also appear to explain observations suggesting that the Universe contains denser structures than predicted.

“The first thing you would expect is that giving dark matter an additional attractive force should make structures grow faster,” says Weiner. “But another effect comes into play at the same time.”

A Surprising Effect on Cosmic Growth

In the models examined by the researchers, the extra force does make dark matter cluster more effectively. However, it also changes how dark matter behaves as the Universe expands.

The same process causes dark matter particles to effectively lose mass over time. This reduction weakens their gravitational influence, offsetting the stronger attraction produced by the hidden force.

As a result, the enhanced clustering does not create a stronger gravitational imprint on the cosmic microwave background. In most cases, the combined effect actually suppresses the growth of cosmic structure.

Implications for DESI and Dark Energy Models

The findings could matter for theories that extend beyond dark matter alone. Some explanations proposed for recent measurements from the Dark Energy Spectroscopic Instrument (DESI) involve similar interactions among dark matter particles.

According to the researchers, the newly identified mechanism is likely to influence many of those more complicated models as well. Any theory involving a hidden attractive force may need to account for the possibility that dark matter becomes effectively lighter as the Universe evolves.

More precise measurements from upcoming observatories and cosmic surveys could help scientists determine which hidden interactions dark matter might possess and which possibilities observations can rule out.

“The Universe is often more subtle than our intuition,” says Weiner. “That’s exactly why we have to keep testing these ideas.”

The findings support once weekly brisk interval walking as a practical therapeutic option for adults with central obesity, especially those who have difficulty fitting several workouts into their schedules. The study was published in Nature Communications.

A More Practical Approach to Reducing Body Fat

Obesity is a chronic health condition involving an unhealthy buildup of body fat. Fat that accumulates around the abdomen is especially concerning because it is associated with cardiovascular disease, metabolic disorders, and a higher risk of premature death.

Exercise plays an important role in managing obesity and offers a wide range of health benefits. Even so, many people, particularly those living with obesity, struggle to maintain regular physical activity over time.

Interval training alternates between more vigorous periods of exercise and lower-intensity periods of active recovery. Research has shown that it can be a time-efficient way to reduce overall body fat and visceral fat compared with continuous exercise performed at a moderate intensity.

Most exercise recommendations call for interval training three days each week. That schedule may be difficult for people with demanding jobs, family responsibilities, limited time, or restricted access to exercise facilities.

Previous research has suggested that a “weekend warrior” pattern, in which most weekly exercise is completed over one or two days, can still produce health benefits. However, there has been relatively little evidence showing whether interval training remains effective when concentrated into a single weekly session.

Professor Parco Siu Ming-fai, Professor and Head of Division of Kinesiology at the School of Public Health, HKUMed, said it was important to determine whether once weekly interval training could match the results of a traditional three-session schedule and provide a more accessible alternative.

One Session Versus Three

From September 2021 to September 2024, the HKUMed team carried out a randomized trial in Hong Kong involving 315 Chinese adults aged 18 or older. All participants were overweight and had central obesity.

Participants were assigned to one of three groups. One group completed interval training once each week, another completed interval training three times each week, and the third served as a control group.

The control group took part in a 2.5-hour health education session every two weeks for four months. Both exercise groups completed a total of 75 minutes of interval training each week. One group performed the full amount in a single session, while the other divided it across three sessions.

Researchers measured body fat using dual-energy X-ray absorptiometry at three stages: before the program began (baseline), after 16 weeks (post-intervention), and at 32 weeks (four-month post-intervention follow-up).

Similar Fat Loss and Fitness Benefits

At the 16-week assessment, both interval training groups showed similar improvements. Participants who exercised once per week and those who exercised three times per week reduced total body fat mass, body fat percentage, and waist circumference. Both groups also improved their cardiorespiratory fitness compared with the control group.

“While thrice-weekly interval training remains a commonly recommended approach for the therapeutic management of excess adiposity, our findings show that once-weekly interval training offers similar benefits and represents a practical exercise strategy,” said Professor Siu. “For many adults with central obesity who struggle to balance work, study, family and other commitments, time constraints are a primary barrier to exercising multiple days per week.”

“Instead of relying solely on high-frequency exercise prescriptions, once-weekly interval training can be considered a feasible and effective alternative,” added Professor Siu.

The study was led by Professor Parco Siu Ming-fai, Professor and Head of Division of Kinesiology at the School of Public Health, HKUMed. The co-first authors were Dr. Leung Chit-kay and Mr. Joshua Bernal, both from the same School.

The research was supported by the General Research Fund of the Research Grants Council, the University Grants Committee of Hong Kong, China, and the Seed Fund for Basic Research, HKU.

Over the past decade, global temperatures have risen at an estimated pace of about 0.35°C per decade, depending on the dataset used. By comparison, the average warming rate from 1970 to 2015 was just under 0.2°C per decade. The recent pace is higher than that of any previous decade since instrumental temperature records began in 1880.

Scientists Isolate the Long-Term Warming Signal

“We can now demonstrate a strong and statistically significant acceleration of global warming since around 2015,” says Grant Foster, a US statistics expert and co-author of the study, which was published today in the scientific journal Geophysical Research Letters.

“We filter out known natural influences in the observational data, so that the ‘noise’ is reduced, making the underlying long-term warming signal more clearly visible,” Foster added.

In climate data, “noise” refers to short-erm temperature changes that can temporarily hide or exaggerate the underlying trend. El Niño, for example, can push global temperatures higher for a limited period by releasing heat from the tropical Pacific Ocean into the atmosphere. Volcanic eruptions can have the opposite effect by sending particles into the atmosphere that reflect sunlight, while changes in the Sun’s activity can also produce smaller temperature variations.

To separate these temporary influences from the broader warming trend, the researchers analyzed measurements from five widely used global temperature data sets (NASA, NOAA, HadCRUT, Berkeley Earth, ERA5).

“The adjusted data show an acceleration of global warming since 2015 with a statistical certainty of over 98 percent, consistent across all data sets examined and independent of the analysis method chosen,” explains Stefan Rahmstorf, PIK researcher and lead author of the study.

Warming Acceleration Appears Across Five Datasets

A statistical certainty of more than 98 percent means the researchers found strong evidence that the change in the warming rate is real rather than the result of random variation in the data. The same overall pattern appeared in all five temperature records, even though the datasets are produced by different scientific organizations and use somewhat different methods.

After the researchers adjusted for El Niño and the solar maximum, the extreme warmth of 2023 and 2024 was reduced slightly in the analysis. Even so, both years remained the two warmest since instrumental records began.

Across all of the datasets, the acceleration started to become visible in 2013 or 2014. The researchers describe the broader shift as beginning around 2015, when the evidence became clearer.

Two Statistical Methods Point to the Same Shift

To determine whether the warming rate had changed since the 1970s, the team used two statistical approaches. The first was a quadratic trend analysis, which tests whether the temperature curve is bending upward over time rather than rising at a constant rate.

The second was a piecewise linear model. This method divides the temperature record into separate periods and objectively identifies when the rate of warming appears to change. Both approaches supported the conclusion that global warming has accelerated.

Study Does Not Identify the Cause

The research was designed to detect and measure the statistical acceleration, not to determine exactly why it has occurred.

However, the authors noted that climate models can produce periods in which warming speeds up. In other words, an increasing rate of warming is consistent with the range of behavior represented in current climate modeling.

Climate models are computer simulations that use the laws of physics to estimate how the atmosphere, oceans, ice, and land respond to greenhouse gases and other influences. They do not predict every short-term fluctuation perfectly, but they help scientists evaluate long-term climate patterns and possible future changes.

1.5°C Threshold Could Be Exceeded Before 2030

“If the warming rate of the past 10 years continues, it would lead to a long-term exceedance of the 1.5°C limit of the Paris Agreement before 2030,” says Stefan Rahmstorf. “How quickly the Earth continues to warm ultimately depends on how rapidly we reduce global CO2 emissions from fossil fuels to zero.”

The 1.5°C limit refers to the goal of restricting long-term global warming to 1.5°C above preindustrial temperatures. A single year above that level does not by itself mean the Paris Agreement threshold has been permanently crossed. Scientists generally focus on sustained warming over a longer period.

The findings suggest that Earth may now be warming considerably faster than it did during the final decades of the 20th century. Whether that acceleration continues will depend heavily on future carbon dioxide emissions from coal, oil, and natural gas.

The researchers found that daily avocado consumption was linked to a lower concentration of low-density lipoprotein (LDL) particles in the blood. These particles carry cholesterol throughout the body. The size of the reduction was associated with an estimated 4% decrease in heart disease risk.

“If people want to improve the quality of their diet, making one small change might be a more feasible strategy than attempting to change their entire diet,” said Janhavi Damani, postdoctoral scholar at Penn State and first author of the study. “For people with obesity, including avocados in their daily diet might be a good starting place.”

LDL Particle Count Can Reveal Hidden Heart Risk

LDL particles are not the same measurement as LDL cholesterol, often called “bad cholesterol.” Both are associated with cardiovascular disease, but particle concentration can reveal risk that a standard cholesterol test may not show. The researchers noted that this risk is often greater in people with abdominal obesity.

LDL cholesterol cannot travel through the bloodstream on its own. It must be carried by protein particles. A person with more LDL carrying particles may face a greater risk of heart disease, even when their total amount of LDL cholesterol is the same as someone with fewer particles.

“Imagine two people with the same high levels of LDL cholesterol,” Damani said. “Person A carries their cholesterol in fewer, larger LDL particles, and Person B carries their cholesterol in more, smaller LDL particles. Person B’s heart disease risk would be higher because their overall particle count is higher even though a test of their LDL cholesterol would look identical.”

Smaller LDL particles can more easily enter artery walls and contribute to plaque buildup, Damani explained. Plaque narrows blood vessels and makes them less flexible, increasing the strain on the cardiovascular system.

When the heart must work harder because of exercise, heat, stress or another cause, stiffened blood vessels may be less able to accommodate the increased blood flow. Blood pressure can then rise more sharply, potentially contributing to a cardiac event such as a heart attack.

Testing One Avocado a Day

For the new analysis, the team examined data from 786 participants enrolled in the Habitual Diet and Avocado Trial. The six-month study included adults ages 25 and older.

Men qualified for the study if their waist circumference was greater than 40 inches, while women were eligible if their waist circumference exceeded 35 inches.

Half of the participants were asked to continue their usual diets and physical activity. The remaining participants also maintained their normal routines but received one avocado to eat every day.

Earlier results from the Habitual Diet and Avocado Trial showed that adding a daily avocado did not reduce body weight or waist circumference in people with obesity. However, it appeared to lower LDL cholesterol levels.

Daily Avocados Lowered LDL Particle Levels

For the current study, researchers compared blood samples collected at the beginning and end of the six-month trial.

Among participants assigned to eat one avocado per day, LDL particle concentrations fell by 49 nanomoles per liter. According to the researchers, that change corresponds to an estimated 4% reduction in heart disease risk.

“Four percent is a modest reduction compared with the 14-29% lower heart disease risk associated with improving the overall diet,” Damani said. “However, it is a step in the right direction.”

The improvement in LDL particle levels was consistent across participants. Sex, race, ethnicity, age and body mass index did not significantly affect the likelihood of experiencing the benefit.

The findings suggest that adults with obesity from a wide range of backgrounds could potentially benefit from including avocados in their diets. However, the researchers advised people to speak with a registered dietitian nutritionist or physician for personalized guidance before making dietary changes.

A Benefit Seen in Real World Diets

Previous Penn State research also found that avocado consumption could lower LDL cholesterol and LDL particle levels. In that earlier experiment, however, researchers closely controlled everything the participants ate.

“Penn State researchers demonstrated several years ago that avocado consumption could reduce LDL cholesterol and levels of LDL particles,” said Kristina Petersen, associate professor of nutritional sciences and senior author of this study. “But in that study, the researchers controlled participants’ entire diets throughout the experiment. This study demonstrated benefits in the real world, where people’s diets are much less predictable. In the course of people’s normal lives, avocado consumption still contributes to a healthier diet.”

The latest findings indicate that a single, manageable change may improve one measure of cardiovascular health even when the rest of a person’s diet remains largely unchanged. The benefit was modest and did not lead to weight loss, but the researchers said it could still represent progress toward better heart health.

Penny Kris Etherton, retired Evan Pugh University Professor of Nutritional Sciences at Penn State, also contributed to the research.

Other co-authors include Nirupa Matthan of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University; Zhaoping Li of the David Geffen School of Medicine at University of California, Los Angeles; Joan Sabaté of the School of Public Health at Loma Linda University; and David Reboussin of the Wake Forest University School of Medicine.

The Avocado Nutrition Center supported this research.

Researchers at McMaster University have now identified a biological pathway that could help explain why these muscle symptoms develop. The finding may eventually lead to treatments that make statins easier to tolerate without reducing their important cardiovascular benefits.

Published in Science Advances, the study points to a previously unrecognized interaction between the immune system and muscle cell metabolism. The mechanism appears to contribute to muscle damage caused by statins and challenges earlier ideas about the origins of these side effects.

Why Statin Side Effects Matter

“Statins are among the most effective medications we have for reducing cardiovascular disease risk and preventing early death,” said Jonathan Schertzer, professor in McMaster’s Department of Biochemistry and Biomedical Sciences and senior author of the study.

“Unfortunately, muscle side-effects lead some people to reduce their dose or stop taking the medication altogether. We wanted to understand why this happens and whether it might be possible to separate the side-effects from the benefits.”

An estimated seven to 29 percent of statin users experience muscle-related symptoms. Although the connection between statins and muscle problems has been recognized for years, scientists have not fully understood the biological processes responsible.

Statins Can Disrupt Muscle Cell Energy

The research was led by first authors Nazli Robin and Nicole Barra of the Schertzer Lab at McMaster. Their team found that statins can interfere with the way muscle cells generate energy.

That disruption appears to activate an immune response inside the muscle cells, leading to tissue damage. In experiments involving muscle cells and mouse models, the researchers prevented much of the damage by blocking the immune response.

“One of the most exciting findings of the research is that the mechanism causing muscle side-effects appears to be separate from the mechanism that lowers cholesterol,” said Schertzer. “That suggests it may one day be possible to target the side-effects without interfering with the cardiovascular benefits that make statins so valuable.”

A Surprising Connection Between Immunity and Metabolism

The findings also uncovered an unexpected relationship between metabolism and the immune system. Changes in the way muscle cells processed energy caused the cells to activate their own immune response.

This discovery offers new insight into how inflammation may contribute to medication side effects. It also suggests that scientists could potentially protect muscle tissue by targeting the immune pathway while leaving the cholesterol-lowering effects of statins intact.

More research is needed before the findings can be developed into treatments for patients. Still, the newly identified pathway provides several possible targets for medications designed to prevent statin intolerance.

“These findings give us a clearer understanding of why some patients experience muscle symptoms and provide promising directions for making these important medications safer and more effective in the future,” added Schertzer.

An International Research Collaboration

The project involved researchers from the Centre International de Recherche en Infectiologie (CIRI) in Lyon, France; the Centre for Muscle Research at the University of Melbourne, Australia; the Murdoch Children’s Research Institute and The Royal Children’s Hospital in Australia; York University in Canada; and McMaster’s Department of Pathology and Molecular Medicine.

The research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC).