January 17, 2011

Fight the Flu with More CO2

Filed under: Adaptation, Plants

Like it or not, winter is here and with it comes the dreaded cold/flu season. We have heard it since we were kids—wash your hands, get plenty of rest, avoid folks who are already sick, and drink lots of orange juice to maintain higher levels of vitamin C. We are skeptical of just about everything, and if one seriously addresses the issue of vitamin C reducing the misery of having the flu, be advised that some studies in adults have shown that taking high doses of vitamin C daily may significantly reduce cold and flu symptoms. Other studies have seen a modest benefit in reducing the duration of a cold or flu symptoms, and a few studies in adults and children have shown that taking vitamin C might help prevent colds or flu, although the research is inconsistent.

It ultimately does not matter whether vitamin C can or cannot prevent or ease cold and flu symptoms, because it offers numerous health benefits when consumed through eating enough fruits and vegetables (3 or more cups per day). Plus, vitamin C acts as a cell-protecting antioxidant and an immune booster, which means it will help keep you healthy anyway—even if it is not a magic elixir for colds and flu specifically. Just remember to sidestep the supplements and stick to whole foods—especially vitamin C-rich foods such as strawberries, oranges, sweet red peppers, and broccoli—when you want to make sure you or your child gets enough of this powerful nutrient.

Given all the biological benefits of elevated atmospheric concentrations of carbon dioxide (CO2), we wondered if we could be so lucky to have CO2 increase the vitamin C of various fruits. Our search for an answer ended quickly when we discovered an article in Agriculture, Ecosystems and Environment entitled “The effect of elevated atmospheric CO2 on the vitamin C concentration of (sour) orange juice.”

And while this study may be a bit of an oldie (published in 2002), the results are such a goodie, that we couldn’t resist dusting them off and shining them up!

The research reports the result of 12 years of growing sour orange trees in conditions of elevated carbon dioixde levels. The experiment was conducted by eight scientists with US Water Conservation Laboratory in Phoenix, the Citrus and Subtropical Products Laboratory in Florida, the Citrus Research and Education Center also in Florida, the Human Nutrition Research Center in Maryland, and the Department of Plant Biology at Arizona State University. The authors acknowledge that funding for the research was provided by the US Department of Agriculture’s Agricultural Research Service and the US Department of Energy. We were a bit surprised to find funding from the Department of Energy, but let’s face it, drinking orange juice definitely gives us energy!

Idso et al. begin their piece noting “Atmospheric CO2 enrichment typically enhances the growth rates of almost all plants, especially trees, even in the face of resource limitations and environmental stresses. In an agricultural context, this phenomenon generally leads to increased edible biomass production. Much less, however, is known about the effects of elevated concentrations of atmospheric CO2 on the nutritive value of food.” Accordingly, the team embarked on a long-term experiment growing sour orange trees in open-top chambers in Phoenix for over a decade with atmospheric CO2 maintained at 400 ppm and 700 ppm. Can you guess why they grew sour oranges? If you don’t know, sour oranges are not likely to be picked and eaten by any staff members looking for a quick treat (they are definitely called sour oranges for a reason)—grow Valencia, Mandarin, or navel oranges in the chambers and they would have run the risk of fruit unexpectedly disappearing from the trees!

The elevated CO2 produced nothing short of a miracle! Imagine claiming you have found a way to have orange trees nearly double their fruit output—would you label the cause (elevated CO2) a pollutant? Now imagine claiming you had found a way to have orange trees increase the vitamin C of the fruit—again, would you conclude the trees were coping with a pollutant (atmospheric CO2)?

Idso et al. explain:

“Based upon these data, it has been determined that when the 75% increase in the air’s CO2 concentration doubles fruit production, it increases the vitamin C concentration of the juice of the fruit by 7%. This nutritional enhancement is even greater in years when fruit production is more than doubled, due to the CO2-enriched fruit being slightly smaller than the ambient-treatment fruit in such circumstances, which increases the vitamin C concentration of the juice of the CO2-enriched fruit. In years when the CO2-induced increase in fruit production is less than 100%, however, the CO2-enriched fruit are generally slightly larger than the ambient-treatment fruit, which reduces the CO2-induced increase in juice vitamin C concentration below the basic 7% level characteristic of fruit of identical size. In what appears to be an approach to long-term equilibrium conditions, five of the last 6 years have seen the CO2-induced increase in the number of fruit produced hover at 74±9%, while the CO2-induced increase in fruit fresh weight has averaged 4±2% and the CO2-induced increase in juice vitamin C concentration has averaged 5 ± 1%.”

So while others are convinced we need to consider atmospheric CO2 a pollutant, Idso et al. conclude:

“In light of the findings of this long-term experiment, there is reason to believe that an atmospheric CO2 enrichment of the magnitude expected over the current century may induce a large and sustained increase in the number of fruit produced by orange trees, a small increase in the size of the fruit, and a modest increase in the vitamin C concentration of the juice of the fruit, all of which effects bode well for this key agricultural product that plays a vital role in maintaining good health in human populations around the globe.”

And although this study was published back in 2002 and reported on data from 12 years of growing sour orange trees in elevated CO2 conditions, the results were little changed when the experiment came to an end in January 2005 with the closure of the U.S. Department of Agriculture-Agriculture Research Service labs in which the trees had been grown for 17 years—the longest running continuous CO2-enrichment study to that point in time. In the experiment’s final report (Kimball et al., 2007), summed things up this way:

When summed over the duration of the experiment, there was an overall enhancement of 70% of total biomass production. Much of the enhancement came from greater numbers of fruits produced, with no change in fruit size.

Call CO2 a pollutant if you’d like, but as seen in this article, CO2 vastly increases the amount of fruit and even increases the nutrients within the fruit—hardly a pollutant in our eyes, but instead something more akin to Miracle-Gro!


Idso, S.B., B.A. Kimball, P.E. Shaw, W. Widmer, J.T. Vanderslice, D.J. Higgs, A. Montanari, and W.D. Clark. 2002. The effect of elevated atmospheric CO2 on the vitamin C concentration of (sour) orange juice. Agriculture, Ecosystems and Environment, 90, 1–7.

Kimball, B., A., et al., 2007. Seventeen years of carbon dioxidce enrichment of sour arrange trees: final results. Global Change Biology, 13, 2171-2183.

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