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Guest Editorial: Elevated CO2 Will Affect Human Nutrition
Volume 5, Number 47: 20 November 2002

I am responding to Idso et al.'s Editorial of 30 October 2002, where they discuss my recent paper on the effects of rising CO2 on human nutrition (Loladze, 2002).  With all due respect to the Idsos, I disagree with their interpretation of my claims.  For the sake of clarity, I note that my arguments do not rely in any way on the effects of increasing CO2 on climate, but on the indisputable fact that atmospheric CO2 concentrations have increased since pre-industrial times and are likely to increase further in the decades ahead.

The Idsos state that micronutrients that "are important to human health ... are currently present in common food plants in what are believed - by some - to be insufficient quantities."  They claim that it is my "assumption that certain essential micronutrients should be present in plants at concentrations that are greater than, or at least equal to, their current concentrations."

Let us look at one of the microelements - iron.  The World Health Organization (2002a) reports that "iron deficiency is the most common nutritional disorder in the world" and that "the numbers are staggering: as many as 4-5 billion people, 66-80% of the world's population, may be iron deficient."  Iron deficiency is among the ten leading global risk factors and causes 800,000 (1.5 per cent) of deaths worldwide (World Health Organization, 2002b).  The evidence of widespread zinc and iodine deficiencies is overwhelming as well (UN ACC/SCN in collaboration with IFPRI 2000, World Health Organization, 2002b).

Plants are the foundation of human nutrition.  They are the major source of microelements; and for large parts of the human population, they are almost an exclusive source of iron, zinc and, in places where iodized salt is not available, of iodine.  Undoubtedly, the world would benefit from a higher content of these elements in staple crops, and it would suffer consequences if levels of essential microelements were to drop.  The synergetic effect of the decline of multiple essential elements simultaneously in many crops is particularly worrisome.  Graham et al. (2000) stress that "by nutritionally enhancing cereals, severe deficiencies can be eliminated in developing countries where largely cereal-based diets are consumed," and even in industrialized countries, nutritionally enhancing cereals "could be important amongst women and children in lower socio-economic groups."  Frossard et al. (2000) state that "increasing the total amount of minerals in edible parts of crops" is one way to increase their bioavailability to humans and combat 'hidden hunger.'  While billions of people suffer from a problem that is beyond any reasonable dispute, the Idsos irresponsibly refer to it as my "assumption" and to be "believed - by some".  I note that the total content of a microelement in food defines only a potentially available maximum for humans, but phytic acid or phenolic compounds present in plant tissues can make actual bioavailability even lower.

The Idsos ask: "Does Loladze not realize that it is not the elements that do the life-sustaining work of plants and animals, but rather the complex compounds that are constructed from them?"  Yes, I do realize that, and that is one of the reasons I wrote the paper: a dietary deficiency of just one element disrupts the work of all complex compounds in a human body that rely on it.  Do the Idsos not realize that?

Obviously, complex compounds are made of individual chemical elements.  So why is it important to look specifically at those elements?  Let us make a comparison with the English language.  There are, at the very least, a quarter of a million distinct English words; yet all of these words are constructed from only 26 letters.  For many instances, from designing keyboards to deciphering secret codes, letters and their relative frequency in the language become crucial.  For example, I am now typing these very words using QWERTY keyboard, the design of which stems from the relative frequency of the 26 letters of the English language.  If one of the keys breaks, that will impede my writing far more severely than a loss of many words.  Similarly, a cell contains thousands of complex substances, but all life forms require less than three dozen elements.  And the deficiency of a single element puts an enormous strain on life's machinery.  Hence, by looking at elements and their relative ratios in organisms and their environment, one can gain insights that are hardly possible to obtain by other means.  Indeed, these principles are pillars in the emerging science of ecological stoichiometry, which is laid out in a remarkable new book that was published just last week (Sterner and Elser, 2002).

Yet, there is an instance where the Idsos themselves support their arguments by looking at an individual element.  They hail increased nitrogen use efficiency of plants (which means lower nitrogen concentrations in plant tissues) as one of the benefits of rising CO2.  I unequivocally agree with the Idsos that elevated CO2 concentrations benefit the overwhelming majority of plants, at least when plants grow in monocultures.  However, they seem to miss the central point: what is good for plants can be bad for their consumers!

The Idsos say I am "the latest fatality in a long line of Cassandras ... who consistently have been proven wrong by real-world data."  According to Greek mythology, however, Cassandra's predictions where accurate, but her warnings went unheeded.  Moreover, all published "real-world data" support my claim.  However, I stress the extreme scarcity of data.  Consider this fact: grains provide over half of all calories worldwide; but only four (4!) published studies exist on the effects of elevated CO2 on elemental composition of grains (Manderscheid et al., 1995; Seneweera and Conroy, 1997; Fangmeier et al., 1999; De la Puente et al., 2000), and all four of them confirm my claim that high CO2, as a rule, alters plant stoichiometry.  Moreover, the data show that the overall concentrations of microelements decline when atmospheric CO2 rises.  In addition, a new report by Fangmeier et al. (2002), which is based on a large study of the second most important crop in Europe (potato), shows an overall decline in the concentrations of almost all measured essential elements in both foliage and tubers under elevated CO2 conditions.  We can only wish that further studies will not confirm such alarming declines.  Otherwise, rising CO2 will aggravate 'hidden hunger' - the leading nutritional disorder in the world.

In conclusion, I think the Idsos agree with me on this fundamental but startlingly under-researched issue: the ongoing increase in the atmosphere's CO2 concentration will affect human nutrition and health by altering the chemical composition of plants - the fundamental food source for humanity.

Irakli Loladze, Ph.D.
Ecology & Evolutionary Biology
Princeton Environmental Institute
Princeton University
Princeton, NJ 08544-1003

De la Puente, L. S., Perez, P.P., Martinez-Carrasco, R., Morcuende, R.M. and Del Molino, I.M.M.  2000.  Action of elevated CO2 and high temperatures on the mineral chemical composition of two varieties of wheat.  Agrochimica 44: 221-230.

Fangmeier, A., De Temmerman, L., Black, C., Persson, K. and Vorne, V.  2002.  Effects of elevated CO2 and/or ozone on nutrient concentrations and nutrient uptake of potatoes.  European Journal of Agronomy 17: 353-358.

Fangmeier, A., De Temmerman, L., Mortensen, L., Kemp, K., Burke, J., Mitchell, R., van Oijen, M. and Weigel, H.J.  1999.  Effects on nutrients and on grain quality in spring wheat crops grown under elevated CO2 concentrations and stress conditions in the European, multiple-site experiment 'ESPACE-wheat'.  European Journal of Agronomy 10: 215-229.

Frossard, E., Bucher, M., Machler, F., Mozafar, A. and Hurrell, R.  2000.  Potential for increasing the content and bioavailability of Re, Zn and Ca in plants for human nutrition.  Journal of the Science of Food and Agriculture 80: 861-879.

Graham, R.D., Humphries, J.M. and Kitchen, J.L.  2000.  Nutritionally enhanced cereals: A sustainable foundation for a balanced diet.  Asia Pacific Journal of Clinical Nutrition 9: S91-S96.

Loladze, I.  2002.  Rising atmospheric CO2 and human nutrition: toward globally imbalanced plant stoichiometry?  Trends in Ecology & Evolution 17: 457-461.

Manderscheid, R., Bender, J., Jager, H.J. and Weigel, H.J.  1995.  Effects of season long CO2 enrichment on cereals.  2. Nutrient concentrations and grain quality.  Agriculture Ecosystems & Environment 54: 175-185.

Seneweera, S. P. and Conroy, J.P. 1997. Growth, grain yield and quality of rice (Oryza sativa L.) in response to elevated CO2 and phosphorus nutrition (Reprinted from Plant nutrition for sustainable food production and environment, 1997).  Soil Science and Plant Nutrition 43: 1131-1136.

Sterner, R. W. and Elser, J.J.  2002.  Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere.  Princeton University Press, Princeton, NJ.

UN ACC/SCN in collaboration with IFPRI.  2000.  Fourth Report on the World Nutrition Situation, Geneva, Switzerland.

World Health Organization.  2000a.  Battling Iron Deficiency Anaemia.  Geneva, Switzerland.  Available at

World Health Organization.  2002b.  The World Health Report 2002: Reducing Risks, Promoting Healthy Life.  Geneva, Switzerland.