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Global Warming May Dwindle the Supply of a Key Brain Nutrient

Health + Wellness
Global Warming May Dwindle the Supply of a Key Brain Nutrient
Char and sockeye salmon moving upstream. Salmon are high in the omega-3 fatty acid DHA. Jonny Armstrong / USGS

By Bret Stetka

Glaciers continue to melt. Sea levels are on the rise. And now scientists believe the changing climate may put our brains at risk. A new analysis predicts that by 2100, increasing water temperatures brought on by a warming planet could result in 96 percent of the world's population not having access to an omega-3 fatty acid crucial to brain health and function.


That molecule is called docosahexaenoic acid, or DHA. It is the most common fatty acid in the mammalian brain and plays a key role in the survival and function of our neural cells, especially during the organ's development. Data suggest that not having enough of the compound may increase the risk of conditions such as depression and attention deficit hyperactivity disorder and impair cognition in people with early dementia.

Our bodies do not make much DHA, so, for the most part, we obtain it through diet. Plants and meats have modest amounts of the fatty acid, but the most abundant source by far is fish (or fish-derived supplements). Fish obtain DHA by consuming algae. The authors of the new study predict that rising temperatures could disrupt algal DHA production and lead to a 10 to 58 percent reduction in availability of the compound, depending on the geographic region.

To predict the future of DHA availability, they used data from the Food and Agriculture Organization of the United Nations and the fishery research institute Sea around Us to get numbers on how much edible fish are caught and farmed worldwide each year and on how much of that maritime tonnage is composed of DHA-containing fat. Then, using data showing how temperature influences algal DHA production, the researchers determined roughly how much of the fatty acid is presently available by consuming fish per capita versus how much will be available 80 years from now.

Their predictions show that larger countries with rapid population growth in East and Southeast Asia — including China, Japan and Indonesia — will face the most severe DHA shortages. Most African countries — especially landlocked ones — will also end up falling below recommended DHA intake, whereas nations with small populations and active fishing industries, such as Norway, Chile and New Zealand, will likely maintain access to adequate omega-3s.

"I already had an idea that DHA would decrease, based on previous data," recalls Stefanie Colombo, an assistant professor in aquaculture nutrition at Dalhousie University and co-lead author on the new paper. "But I was surprised and concerned when we saw the decline in DHA per capita—that people in some areas of the world would be more affected."

Tom Brenna, a professor with joint appointments in pediatrics, chemistry and human nutrition at the University of Texas at Austin, points out that the new results are open to a range of interpretation: "The [predicted] interval of 10 to 58 percent is so large as to be the difference between a mild inconvenience and a calamity." Yet he welcomes any investigation into the global DHA supply.

Brenna, who was not involved in the new study, also points out that whether or not dietary DHA is necessary in adults has been an area of conflict for decades. Yet he and most experts in the field agree that it is a critical nutrient during brain development and even into the late teen years — and that its influence on brain function may vary, based on an individual's genetic profile.

Omega-3 fatty acids can be derived from terrestrial sources, including nuts, seeds and land animals. Yet as Michael Crawford, now at Imperial College London, discovered in the 1970s, "ready-made" DHA — such as found in fish — is incorporated into the developing brain with 10-fold greater efficiency than plant-sourced DHA.

Crawford is a pioneer in understanding the relationship between omega-3 fatty acids and brain health and believes that the evolution of our big and complex primate brain would have been impossible without access to DHA. He also thinks that a decline in consumption of omega-3s because of our increasingly processed diet explains increasing rates of mental illness and declining IQ. Marine agriculture such as projects now underway in Japan might be essential to saving ourselves and the planet. "If mental illness continues to escalate, then Homo sapiens are finished," Crawford predicts. "Seventy-one percent of the planet's surface is water, and marine cultivation will help reverse this trend. Without farming the seabed and oceans, food security goes out of the window."

Aquaculture initiatives abound throughout the world, including those intent on farming algae as a source of DHA. Other researchers are using genetic engineering to grow plants with a more available form of the fatty acid. And Richard P. Bazinet, a professor in the department of nutritional sciences at the University of Toronto and a co-author of the new paper, is working to understand how DHA enters the brain and how much of it a healthy adult brain actually needs.

Colombo is hopeful that in the face of a changing climate, scientists will devise new sources of DHA. And she plans to study how warming waters will affect fish metabolism and DHA availability. Yet she admits the outcome does not look good: "I don't think this is something we can ignore. In terms of the climate warming, we can't continue on this same trajectory."

This story originally appeared in Scientific American. It is republished here as part of EcoWatch's partnership with Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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