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The Cancer-Kale Connection: What's CO2 Got To Do With It?
Volume 12, Number 51: 23 December 2009

In an important new paper, La et al. (2009) write that "epidemiological studies show that there is a negative relationship between Brassicaceae vegetable intake and the risk of a number of cancers (Wattenberg, 1993; Kohlmeier and Su, 1997; Price et al., 1998)" and that "it has been widely recognized that some of the cancer-chemoprotective activities in these vegetables are attributable to their contents of glucosinolates (GSs) (Zhao et al., 1992; Wattenberg, 1993; Tawfiq et al., 1995; Fahey et al., 1997; Rosa et al., 1997; Holst and Williamson, 2004)." Hence, they decided to see what effect the ongoing rise in the air's CO2 content might have on the production of these important cancer-fighting agents.

Working with seedlings of Chinese kale (Brassica alboglabra L. var. Sijicutiao), the five scientists placed them in pairs in 1.8-L pots "fixed in a foam cavity with sponge" within growth chambers maintained at either 350 or 800 ppm CO2, where the plant's roots were immersed in culture solutions treated with either 5.0 mmol nitrogen (N) per L (low N), 10 mmol N per L (medium N), or 20 mmol N per L (high N) and allowed to grow for 35 days, after which the plants were separated into their primary morphological parts and weighed, while their bolting stems were ground into powder for glocosinolate analyses.

"Regardless of N concentration," say the researchers in describing their findings, the elevated CO2 treatment "significantly increased plant height [15.64%], stem thickness [11.79%], dry weights of the total aerial parts [11.91%], bolting stems [15.03%], and roots [16.34%]." In addition, they report that the elevated CO2 increased the total GS concentrations of the bolting stems in the low and medium N treatments by 15.59% and 18.01%, respectively, compared with those at ambient CO2, although there was no such effect in the high N treatment. Thus, in terms of the total amount of GS production within the bolting stems of Chinese kale, these results suggest that increases of 33 to 36% may well be obtained for plants growing in low to medium N conditions in response to a 450-ppm increase in the atmosphere's CO2 concentration.

These results certainly bode well for people who are wise enough to generously partake of Chinese kale -- and, in all probability, other cruciferous vegetables as well -- especially in the CO2-enriched world of the future that seems destined to become a reality, in spite of all that some might perversely do in striving to prevent it.

Sherwood, Keith and Craig Idso

Fahey, J.W., Zhang, Y. and Talalay, P. 1997. Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens. Proceedings of the National Academy of Sciences, USA 94: 10,367-10,372.

Holst, B. and Williamson, G. 2004. A critical review of the bioavailability of glucosinolates and related compounds. Natural Product Reports 21: 425-447.

Kohlmeier L. and Su, L. 1997. Cruciferous vegetable consumption and colorectal cancer risk: meta-analysis of the epidemiological evidence. FASEB Journal 11: 2141.

La, G.-X, Fang, P., Teng, Y.-B, Li, Y.-J and Lin, X.-Y. 2009. Effect of CO2 enrichment on the glucosinolate contents under different nitrogen levels in bolting stem of Chinese kale (Brassica alboglabra L.). Journal of Zhejiang University Science B 10: 454-464.

Price, K.R., Casuscelli, F., Colquhoun, I.J. and Rhodes, M.J.C. 1998. Composition and content of flavonol glycosides in broccoli florets (Brassica oleracea) and their fate during cooking. Journal of the Science of Food and Agriculture 77: 468-472.

Rosa, E., Heaney, R.K., Fenwick, G.R. and Portas, C.A.M. 1997. Glucosinolates in crop plants. Horticultural Reviews 19: 99-215.

Tawfiq, N., Heaney, R.K., Pulumb, J.A., Fenwick, G.R., Musk, S.R. and Williamson, G. 1995. Dietary glucosinolates as blocking agents against carcinogenesis: glucosinolate breakdown products assessed by induction of quinine reductase activity in murine hepa1c1c7 cells. Carcinogenesis 16: 1191-1194.

Wattenberg, L.W. 1993. Food and Cancer Prevention: Chemical and Biological Aspects. Royal Society of Chemistry. London, UK.

Zhao, F., Evans, E.J., Bilsborrow, P.E., Schnug, E. and Syers, J.K. 1992. Correction for protein content in the determination of the glucosinolate content of rapeseed by the XRF method. Journal of the Science of Food and Agriculture 58: 431-433.