Omega-3 fatty acids could be one reason that human brains evolved to be so powerful, but changing water conditions associated with climate change may reduce the amount of omega-3 available for human consumption. A new global tally of the omega-3 fatty acid docosahexaenoic acid (DHA) found it will drop in availability by 10%–58% depending on how aggressively humans curb greenhouse gas emissions over the next century.
Humans get their dietary dose of DHA from eating fish and shellfish. The Food and Agriculture Organization of the United Nations recommends infants consume 100 milligrams per day, and studies advise that adults consume between 50 and 500 milligrams per day (adult dosage is an active area of research). DHA helps with signal transduction in the brain; past research suggests it aids learning in toddlers, and it may be linked with lower rates of Alzheimer’s.
Fish will have lower amounts of DHA because of climate change, said Stefanie Colombo, an assistant professor in aquaculture nutrition at Dalhousie University in Halifax, Canada, and an author on the new study published in Ambio.
Fish get DHA from algae, tiny aquatic organisms that grow in fresh and salt water. Algae use DHA to moderate the fluidity of their body; when the water around them is cold, they avoid freezing by amping up their DHA. Because climate change is warming waters around the world, algae are producing less DHA. In a 2016 study, Colombo and colleagues found a “significant and powerful correlation” between increasing water temperature and the amount of DHA in algae.
The scientists took the research one step further in the latest study, modeling the total DHA in fish around the world over the next century under four different greenhouse gas emissions scenarios.
Under the scenario with increasing greenhouse gas emissions, which most closely aligns with today’s emissions behaviors, “we found that up to 50% of our DHA could decrease in the next 80 years,” Colombo said. “To me, that was the biggest number.”
“An Underappreciated Risk of Global Warming”
High-latitude countries like Norway, Greenland, and Chile are projected to sustain enough fish yields to remain above the daily recommended dose of DHA in 2100. But the new model predicts that countries such as China, Japan, and Indonesia that currently produce enough DHA for their populations will have insufficient stores by the end of the century.
Countries in Africa that rely on inland fisheries will be hit the hardest. Lake and river waters are warming faster than the ocean, and countries that aren’t affluent may not have access to trade or new technologies. Many African countries will produce less than 25 milligrams per person each day by 2100, far below the recommended intake for both infants and adults.
Technologies to combat a reduced amount of DHA are still in their early stages. Early trials on genetically modifying the oilseed in canola oil to include DHA are awaiting approval by U.S. regulatory bodies. Growing algae in controlled environments is often prohibitively expensive, Colombo said.
Humans can’t create their own omega-3 fatty acids but need it in the cell membranes in our neural tissues to facilitate signal transfer among cells. The projected decline in DHA availability “will thus have detrimental effects for human well-being and perhaps even for human evolution,” said Kainz.
Irina Guschina, a research fellow in the School of Biosciences at Cardiff University in Wales who did not participate in the new study, said that the research raises awareness of an “underappreciated risk of global warming.” She cautioned that the recommended dose of DHA for adults is still being debated, however, and that other fatty acids like omega-6 are also important for human health.
Colombo said that how fish react to lower DHA still needs to be tested in the lab, including their metabolic response to warming temperatures. She plans to feed fish in tanks with different levels of DHA and increase their water temperature. “That’s kind of a follow-up study that I probably wouldn’t have done unless we did this model,” she added.
—Jenessa Duncombe (@jrdscience), News Writing and Production Fellow
This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.