Background
The authors write that "the antioxidant properties in food have been a focus of interest in recent years due to the health maintenance functions of these components that can help reduce the risk of chronic diseases such as cancer, hypertension and diabetes," noting that this phenomenon "is attributed to the high scavenging activity of antioxidants towards free radicals that are usually associated with these diseases (Namiki, 1990; Byers and Guerrero, 1995)." For example, "it is currently known," as they continue, "that phenolic acids and flavonoids are antioxidants with high anti-inflammatory and anti-carcinogenic activities (Byers and Guerrero, 1995; Heijnen et al., 2001; Chun et al., 2003)," and that "phenolics and flavonoids can function as free radical scavengers, reducing agents and quenchers of singlet oxygen formation (Chan et al., 2008)," while "the components of polyphenols have been proven to have important roles in the regulation of cancer and disease development in the human body (Harborne and Williams, 2000; Chen, 2004)," proffering the example that in green tea "the effectiveness of the plant extract to inhibit cancer and tumor invasion is due to the high phenolics and flavonoids content in the plant (Sung-Jin et al., 2008)."

What was done
In the words of Ibrahim and Jaafar, "a randomized complete block design 3 by 3 experiment was designed to investigate and distinguish the relationships among production of secondary metabolites (total phenolics, total flavonoids, gluthatione, oxidized gluthatione, soluble carbohydrate and antioxidant activities of the Malaysian medicinal herb Labisia pumila Blume under three levels of CO2 enrichment (400, 800 and 1200 ppm) for 15 weeks."

What was learned
The two University Putra Malaysia researchers report that "secondary metabolites, glutathione, oxidized gluthathione and antioxidant activities in a descending manner came from the leaf enriched with 1200 ppm CO2 > leaf 800 ppm CO2 > leaf 400 ppm CO2 > stem 1200 ppm CO2 > stem 800 ppm CO2 > stem 400 ppm CO2 > root 1200 ppm CO2 > root 800 ppm CO2 > root 400 ppm CO2," and they state that "correlation analyses revealed strong significant positive coefficients of antioxidant activities with total phenolics, flavonoids, gluthatione and oxidized gluthatione," indicating that "an increase in antioxidative activity of L. pumila under elevated CO2 might be up-regulated by the increase in production of total phenolics, total flavonoids, glutathione, oxidized gluthatione and soluble sugar."

What it means
Ibrahim and Jaafar say their study results imply that "the medicinal potential of herbal plants such as L. pumila can be enhanced under elevated CO2, which simultaneously improved the antioxidative activity that was indicated by the high oxygen radical absorbance activity against peroxyl radicals, superoxide radicals, hydrogen peroxide and hydroxyl radicals." Or as we might more simply paraphrase it, more CO2 is good for you!

References
Byers, T. and Guerrero, N. 1995. Epidemilogic evidence for vitamin C and vitamin E in cancer prevention. American Journal of Clinical Nutrition 62: 1385-1392.

Chan, E.W.C., Lim, Y.Y., Wong, L.F., Lianto, F.S., Wong, S.K., Lim, K.K., Joe, C.E. and Lim, T.Y. 2008. Antioxidant and tyrosinase inhibition properties of leaves and rhizomes of ginger species. Food Chemistry 109: 477-483.

Chen, G. 2004. Effect of low fat and/or high fruit and vegetable diets on plasma level of 8-isoprostane-F2alpha in nutrition and breast health study. Nutrition and Cancer 50: 155-160.

Chun, O.K., Kim, D.O. and Lee, C.Y. 2003. Superoxide radical scavenging activity of the major polyphenols in fresh plums. Journal of Agricultural Food and Chemistry 51: 8067-8072.

Harborne, J.B. and Williams, C.A. 2000. Advances in flavonoid research science. Phytochemistry 55: 481-504.

Heijnen, C.G., Haenen, G.R., van Acker, F.A., van der Vijgh, W.J. and Bast, A. 2001. Flavonoids as peroxynitrite scavengers: the role of the hydroxyl groups. Toxicology in Vitro 15: 3-6.

Namiki, M. 1990. Antioxidant/antimutagens in food, critical reviews of food science and nutrition. Food Science and Nutrition 29: 273-300.

Sung-Jin, P., Hoon, M., Young-Youn, K., Jun-Young, P., Jun-Woo, P., Myung-Jin, K. and Soon-Min, H. 2008. Anticancer effects of genistein, green tea catechins, and cordycepin on oral squamous cell carcinoma. Journal of Korean Oral and Maxillofacial Surgery 34: 1-10.