COULD RISING CARBON DIOXIDE LEVELS STRIP FOODS OF SOME NUTRIENTS?

Study suggests significant decline in amounts of zinc, iron as CO2 becomes more abundant in the atmosphere.

As carbon dioxide levels continue to rise around the globe, a new food investigation contends that many of the world's crops will lose vital nutrients.

The new analysis looks at how nutrients found in staple foods, such as wheat, rice, maize, sorghum, soybeans and field peas, hold up when exposed to the amount of carbon dioxide (CO2) that's expected to be in the atmosphere by the year 2050.

"The bottom-line is that our work shows that by 2050 a big chunk of the world's caloric intake will have lost a significant amount of nutrients like zinc and iron that are very important for human nutrition," said lead author Dr. Samuel Myers, a research scientist and instructor in medicine at the Harvard School of Public Health.

"Why this matters is because large vitamin and mineral deficiencies already exist today in about 2 billion people," Myers added. "And the burden of disease associated with these deficiencies is already enormous, particularly in developing countries.

"It's also the case that about 1.9 billion people now receive at least 70 percent of their dietary iron or zinc or both from staple crops like legumes and grains. So we have a major global health problem that's set to get much worse," he said.

Myers and colleagues reported their findings in a research letter published online May 7 in Nature.

Carbon dioxide is a gas that's naturally present in the atmosphere. But, it's also produced as a result of human activities, such as creating electricity and driving cars, according to the U.S. Environmental Protection Agency (EPA). The majority of CO2 now in the atmosphere comes from human activities, according to the EPA. CO2 is one of the heat-trapping gases that's contributing to climate change.

Currently, global carbon dioxide levels hover at around 400 parts per million. This compares with the roughly 280 parts per million level seen during the pre-industrial age, according to Myers.

"But most experts believe that the world will see 550 parts per million by 2050," he said.

Based on that assumption, the study team established seven agricultural sites across Australia, Japan and the United States. In turn, 41 versions of grains and legumes were planted in open-air conditions, with CO2 levels set between 546 and 586 parts per million.

Nutritional testing revealed that some crops -- such as sorghum and maize -- fared better than others, probably due to pre-existing CO2 exposure, the study authors suggested. Some forms of rice also seemed to hang on to their nutritional content despite elevated CO2 levels.

But, many varieties of rice, wheat, peas and soybeans lost significant amounts of iron and zinc. Zinc levels in wheat, for example, dropped by more than 9 percent, with iron dropping by 5 percent. Wheat also saw protein levels fall off by more than 6 percent, the investigators found.

In the end, Myers' team concluded that the nutritional threat posed by carbon dioxide is all too real.

"And I think it's very important not to conflate the CO2 issue with climate change," he said. "Because while climate change is, for some, a matter of vigorous debate in terms of how it will unfold, there is no debate about the simple fact that CO2 in the atmosphere is rising. It's rising. And the nutritional impact we have identified here is entirely dependent on that rise, and nothing else."

So is a nutritional calamity inevitable?

"There are two possible avenues to address the issue," Myers said. "One is to try to contain CO2 levels. But the problem is that the CO2 levels that most people believe we'll see by 2050 are expected regardless of any efforts to mitigate against climate change that might theoretically be taken now, because most of the efforts being discussed are about trying to reduce even higher levels of CO2 in the future."

Myers acknowledged the importance of trying to reduce CO2 levels, but "unless we develop some completely unanticipated technology to remove CO2 from the atmosphere in huge amounts, the nutritional impact we saw will come into play," he said.

"The other avenue is to try and reduce vulnerability by developing crop breeds that are less sensitive to this effect," he suggested. "And there is some grounds for believing that's possible, by, for example, bio-fortifying grains with additional amounts of iron and zinc. Or, on the other hand, launching aggressive global mineral supplementation programs. All of this might help."

Lona Sandon, a registered dietician and assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center at Dallas, said the situation sounded like "big trouble," given how critical iron and zinc are to health.

"Both are essential nutrients," she said. "Without adequate iron we don't effectively produce red blood cells, which are essential for oxygen delivery to the body's tissues. This can turn into anemia, which causes fatigue and greatly impedes quality of life."

And, "zinc is critical for a functioning immune system. Without it you can't fight off a cold or infection, or heal wounds," Sandon added. "So clearly what this study is saying is that we have a big, big problem," she said.

SOURCES: Samuel Myers, M.D., M.P.H., research scientist and instructor in medicine, Harvard School of Public Health, Boston; Lona Sandon, R.D., assistant professor of clinical nutrition, University of Texas Southwestern Medical Center at Dallas; May 7, 2014, Nature, online