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Is the Ongoing Rise in the Air's CO2 Content Enhancing the Health-Promoting Properties of the Food We Eat?
Volume 6, Number 34: 20 August 2003

In response to the question posed in the title of our Editorial, we unabashedly note we have long believed atmospheric CO2 enrichment does indeed elicit changes in food properties that improve human health and promote longevity [see, for example, our Journal Reviews of the papers of Horiuchi (2000) & Tuljapurkar et al. (2000), Melov et al. (2000), Finkel and Holbrook (2000) and Idso et al. (2002), as well as our Editorials of 28 Mar 2001, 30 Oct 2002 and 5 Feb 2003]. So strongly do we believe this to be the case, in fact, we suggested in our Editorial of 5 Feb 2003 that plant scientists "must delve deeper and more extensively into this vitally important area of concern that touches the lives of every inhabitant of the planet," because "the fertile surface of this most important field of research has barely been scratched." Hence, we are pleased to report the results of one of the most exciting of these important scientific "scratchings" to be conducted to date -- the study of Wang et al. (2003), who evaluated the effects of elevated CO2 on the antioxidant activity and flavonoid content of strawberry fruit.

The three scientists who performed the work were all employees of the U.S. Department of Agriculture's Agricultural Research Service. They conducted their research in field plots at the Beltsville Agricultural Research Center, Beltsville, Maryland, USA, where they grew strawberry plants (Fragaria x ananassa Duchesne cv. Honeoye) in six clear-acrylic open-top chambers, two of which were maintained at the ambient atmospheric CO2 concentration, two of which were maintained at ambient + 300 ppm CO2, and two of which were maintained at ambient + 600 ppm CO2 for a period of 28 months (from early spring of 1998 through June 2000). They harvested the strawberry fruits, in their words, "at the commercially ripe stage" in both 1999 and 2000, after which they analyzed them for a number of different antioxidant properties and flavonol contents.

Before reporting what they found, Wang et al. provide some background by noting that "strawberries are good sources of natural antioxidants (Wang et al., 1996; Heinonen et al., 1998)." They further report that "in addition to the usual nutrients, such as vitamins and minerals, strawberries are also rich in anthocyanins, flavonoids, and phenolic acids," and that "strawberries have shown a remarkably high scavenging activity toward chemically generated radicals, thus making them effective in inhibiting oxidation of human low-density lipoproteins (Heinonen et al., 1998)." In this regard, they note that previous studies (Wang and Jiao, 2000; Wang and Lin, 2000) "have shown that strawberries have high oxygen radical absorbance activity against peroxyl radicals, superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen." In their experiment, therefore, they were essentially seeking to see if atmospheric CO2 enrichment could make a good thing even better.

What did the Agricultural Research Service scientists find? They determined, first of all, that strawberries had higher concentrations of ascorbic acid (AsA) and glutathione (GSH) "when grown under enriched CO2 environments." In going from ambient to +300 ppm and +600 ppm CO2, for example, AsA concentrations increased by 10 and 13%, respectively, while GSH concentrations increased by 3 and 171%, respectively. They also learned that "an enriched CO2 environment resulted in an increase in phenolic acid, flavonol, and anthocyanin contents of fruit." For nine different flavonoids, for example, there was a mean concentration increase of 55 23% in going from the ambient atmospheric CO2 concentration to +300 ppm CO2, and a mean concentration increase of 112 35% in going from ambient to +600 ppm CO2. In addition, they report that the "high flavonol content was associated with high antioxidant activity." As for the significance of these findings, Wang et al. note that "anthocyanins have been reported to help reduce damage caused by free radical activity, such as low-density lipoprotein oxidation, platelet aggregation, and endothelium-dependent vasodilation of arteries (Heinonen et al., 1998; Rice-Evans and Miller, 1996)."

In summarizing their findings, Wang et al. say "strawberry fruit contain flavonoids with potent antioxidant properties, and under CO2 enrichment conditions, increased the[ir] AsA, GSH, phenolic acid, flavonol, and anthocyanin concentrations," further noting that "plants grown under CO2 enrichment conditions also had higher oxygen radical absorbance activity against [many types of oxygen] radicals in the fruit." Hence, they determined that atmospheric CO2 enrichment truly did "make a good thing better," as we had long hypothesized would someday be determined to be the case.

In light of these striking findings, we hope other scientists will conduct similar studies of still other fruits and vegetables; for it is imperative that we learn as much as possible about the food-related human health and longevity aspects of the ongoing rise in the air's CO2 content before we mandate reductions in anthropogenic CO2 emissions that could well do the people of the world more harm than good. The scientists and the organization that supported them in this seminal research effort are to be congratulated for their keen insight into this important subject.

Sherwood, Keith and Craig Idso

References
Finkel, T. and Holbrook, N.J. 2000. Oxidants, oxidative stress and the biology of ageing. Nature 408: 239-247.

Heinonen, I.M., Meyer, A.S. and Frankel, E.N. 1998. Antioxidant activity of berry phenolics on human low-density lipoprotein and liposome oxidation. Journal of Agricultural and Food Chemistry 46: 4107-4112.

Horiuchi, S. 2000. Greater lifetime expectations. Nature 405: 744-745.

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

Melov, S., Ravenscroft, J., Malik, S., Gill, M.S., Walker, D.W., Clayton, P.E., Wallace, D.C., Malfroy, B., Doctrow, S.R. and Lithgow, G.J. 2000. Extension of life-span with superoxide dismutase/catalase mimetics. Science 289: 1567-1569.

Rice-Evans, C.A. and Miller, N.J. 1996. Antioxidant activities of flavonoids as bioactive components of food. Biochemical Society Transactions 24: 790-795.

Tuljapurkar, S., Li, N. and Boe, C. 2000. A universal pattern of mortality decline in the G7 countries. Nature 405: 789-792.

Wang, S.Y. and Jiao, H. 2000. Scavenging capacity of berry crops on superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen. Journal of Agricultural and Food Chemistry 48: 5677-5684.

Wang, S.Y. and Lin, H.S. 2000. Antioxidant activity in fruit and leaves of blackberry, raspberry, and strawberry is affected by cultivar and maturity. Journal of Agricultural and Food Chemistry 48: 140-146.

Wang, S.Y., Bunce, J.A. and Maas, J.L. 2003. Elevated carbon dioxide increases contents of antioxidant compounds in field-grown strawberries. Journal of Agricultural and Food Chemistry 51: 4315-4320.