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Breathing very dirty air may boost obesity risk

Beijing smog

Serious air pollution, like this smog over China’s capital city, may increase the risk of obesity.

Air pollution is bad for our lungs. It may not be great for our waistlines either, a new study in rats finds.

China’s capital city of Beijing has some of the worst air pollution in the world. On really bad days, its air can host more than 10 times as many tiny pollutant particles as the World Health Organization says is safe for human health. In a new study, rats breathed in this air. And those rodents gained more weight, and were unhealthier overall, than were rats breathing much cleaner air. The results suggest that exposure to air pollution can raise the risk of becoming extremely overweight.

And, adds Loren Wold, “It is highly likely that this is happening in humans.”

Wold works at Ohio State University in Columbus. There, he studies how air pollution affects the heart. He was not involved in the new study. But he says it agrees with many other studies that have suggested air pollution can affect metabolism, which is how the body breaks down food and uses it for fuel.

Polluted air contains particles of ash, dust and other chemicals. Sometimes these particles are so numerous that they create a thick, dense smog can cuts visibility.

Earlier experiments among 18-year olds in Southern California had linked heavier traffic with higher body mass index (a measure of overweight and obesity). Areas with heavy traffic also tend to have more of those pollutant particles. Another study found that when pregnant mice were exposed to exhaust from diesel engines, their pups grew up to be heavier. The pups also developed more inflammation in their brains.

In the new study, researchers tested how Beijing’s polluted air affects the health of pregnant rats.

Jim Zhang is an environmental scientist at Duke University in Durham, N.C. He and his co-workers put rats in two indoor chambers in Beijing. They piped polluted air from the city directly into one chamber. Air piped into the other chamber went through a filter. That filter removed almost all of the big pollution particles from the air and about two-thirds of the smaller ones. This made the air more like what people breathe in typical U.S. cities and suburbs, Zhang says.

All rats ate the same type and amount of food. But after 19 days, the pregnant rats breathing the heavily polluted air weighed more than the rats breathing the filtered air. They also had higher amounts of cholesterol — a waxy, fatlike substance — in their blood than did the rats breathing filtered air.

Those breathing the dirtier air had higher levels of inflammation. This is a sign of the body responding to tissue damage. These rats also had higher insulin resistance. This means their bodies weren’t responding as well to insulin, a hormone that helps with using sugar for energy. Insulin resistance can lead to diabetes, a dangerous health condition.

Taken together, the scientists say, these symptoms indicate the rats were developing metabolic syndrome. It’s a condition that puts the animals at risk of heart disease and diabetes.

During the experiment, the pregnant rats gave birth. Their pups stayed in the chambers with their mothers. And young rats that breathed in the polluted air were heavier than pups born to moms living in the cleaner air. Like their moms, the pups breathing very polluted air had more inflammation and insulin resistance.

The longer these pups breathed the dirty air, Zhang says, the more unhealthy they became. This suggests that breathing polluted air for a long time can lead to sickness, Zhang says.

It’s not yet clear exactly how air pollution affects rat metabolism. But it seems, Zhang says, to impair how the animals process fat and sugar. Pollution also increases signs of inflammation in the lungs, blood and fat. Zhang says this is probably what led to weight gain in the animals.

Wold says it might be possible to create medicines that reverse the negative health effects of air pollution. But these medicines will take time to develop.

Until then, Zhang and Wold say that paying attention to air pollution levels can help people manage their health risks. On days when pollution levels are high, they recommend that people stay indoors, if possible — or at least avoid tough outdoor exercise .


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Cosmic doom

We’re safe for now. The way the universe is expanding, it won’t be tearing itself apart for at least a few billion years.

For those of you only now discovering that such an end was a possibility, here’s a little background. Observations of stars and galaxies indicate that the universe is expanding, and at an increasing rate. Assuming that acceleration stays constant, eventually the stars will die out, everything will drift apart, and the universe will cool into an eternal “heat death”.

But that’s not the only possibility. The acceleration is thought to be due to dark energy, mysterious stuff that permeates the entire universe. If the total amount of dark energy is increasing, the acceleration will also increase, eventually to the point where the very fabric of space-time tears itself apart and the cosmos pops out of existence.

One prediction puts this hypothetical “big rip” scenario 22 billion years in the future. But could it happen sooner? To find out, Diego Sáez-Gómez at the University of Lisbon, Portugal, and his colleagues modelled a variety of scenarios and used the latest expansion data to calculate a likely timeline. The data involved nearby galaxies, supernovae andripples in the density of matter known as baryon acoustic oscillations, all of which are used to measure dark energy.

The team found that the earliest a big rip can occur is at 1.2 times the current age of the universe, which works out to be around 2.8 billion years from now. “We’re safe,” says Sáez-Gómez.

Time equals infinity

And when is the latest it could happen? “The upper bound goes to infinity,” he says. That would mean the rip never comes and we end up with the heat death scenario instead.

Given that the sun isn’t expected to burn out for at least another 5 billion years, it would be surprising if the universe ended so early. But pondering our doom could be a worthwhile exercise anyway, Sáez-Gómez says. Scenarios like the big rip result from a lack of understanding of physics in particular our inability to marry quantum mechanics and general relativity, the theory of gravity. Exploring the possibilities could show us a way forward.

“You learn more about a physical theory by looking at the exotic and extreme cases,” says Robert Caldwell of Dartmouth College in New Hampshire, who helped come up with the big rip idea. He thinks Sáez-Gómez’s lower bound is very conservative, however – the universe is likely to last much longer. Even if it doesn’t, at least we’ve got a good run ahead of us. he says.

Reference: arxiv.org/abs/1602.06211v1


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Missing Y chromosome kept us apart from Neanderthals

The Y chromosome is a hindrance

Modern humans diverged from Neanderthals some 600,000 years ago – and a new study shows the Y chromosome might be what kept the two species separate.

It seems we were genetically incompatible with our ancient relatives – and male fetuses conceived through sex with Neanderthal males would have miscarried. We knew that some cross-breeding between us and Neanderthals happened more recently – around 100,000 to 60,000 years ago.

Neanderthal genes have been found in our genomes, on X chromosomes, and have been linked to traits such as skin colour, fertility and even depression and addiction. Now, an analysis of a Y chromosome from a 49,000-year-old male Neanderthal found in El Sidrón, Spain, suggests the chromosome has gone extinct seemingly without leaving any trace in modern humans.

This could simply be because it drifted out of the human gene pool or, as the new study suggests, it could be because genetic differences meant that hybrid offspring who had this chromosome were infertile – a genetic dead end.

Four gene mutations

Fernando Mendez of Stanford University, and his colleagues compared the Neanderthal Y chromosome with that of chimps, and ancient and modern humans.

They found mutations in four genes that could have prevented the passage of Y chromosome down the paternal line to the hybrid children.

“Some of these mutations could have played a role in the loss of Neanderthal Y chromosomes in human populations,” says Mendez.

For example, a mutation in one of the genes, KDM5D that plays a role in cancer suppression, has previously been linked to increased risk of miscarriages as it can elicit an immune response in pregnant mothers.

“That could be one reason why we don’t see Neanderthal Y chromosomes in modern human populations,” says Mark Pagel an evolutionary biologist at the University of Reading.

It could also be one factor keeping the two species as separate species.

The researchers also used the new DNA sequences to estimate the time when the most recent common ancestor of Neanderthal and modern human Y chromosomes existed. They came up with a figure of around 590,000 years ago, which agrees with other estimates for the split of the two groups.

 

Journal reference: The American Journal of Human Genetics, DOI: 10.1016/j.ajhg.2016.02.023