Background Increasing concentrations of atmospheric carbon dioxide (CO2) lower the content of zinc and other
nutrients in important food crops. Zinc defi ciency is currently responsible for large burdens of disease globally, and
the populations who are at highest risk of zinc defi ciency also receive most of their dietary zinc from crops. By
modelling dietary intake of bioavailable zinc for the populations of 188 countries under both an ambient CO2 and
elevated CO2 scenario, we sought to estimate the eff ect of anthropogenic CO2 emissions on the global risk of zinc
defi ciency.
Methods We estimated per capita per day bioavailable intake of zinc for the populations of 188 countries at ambient
CO2 concentrations (375–384 ppm) using food balance sheet data for 2003–07 from the Food and Agriculture
Organization. We then used previously published data from free air CO2 enrichment and open-top chamber
experiments to model zinc intake at elevated CO2 concentrations (550 ppm, which is the concentration expected by
2050). Estimates developed by the International Zinc Nutrition Consultative Group were used for country-specifi c
theoretical mean daily per-capita physiological requirements for zinc. Finally, we used these data on zinc bioavailability
and population-weighted estimated average zinc requirements to estimate the risk of inadequate zinc intake among
the populations of the diff erent nations under the two scenarios (ambient and elevated CO2). The diff erence between
the population at risk at elevated and ambient CO2 concentrations (ie, population at new risk of zinc defi ciency) was
our measure of impact.
Findings The total number of people estimated to be placed at new risk of zinc defi ciency by 2050 was 138 million
(95% CI 120–156). The people likely to be most aff ected live in Africa and South Asia, with nearly 48 million (32–63)
residing in India alone. Global maps of increased risk show signifi cant heterogeneity.
Interpretation Our results indicate that one heretofore unquantifi ed human health eff ect associated with anthropogenic
CO2 emissions will be a signifi cant increase in the human population at risk of zinc defi ciency. Our country-specifi c
fi ndings can be used to help guide interventions aimed at reducing this vulnerability