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Carbon Dioxide Levels Will Alter the Protein, Micronutrients, and Vitamin Content of Grains of Rice with Potential Consequences for the Health of the Poorest Rice-Dependent Countries

It has been reported that the response of crops to rising levels of CO₂ is a decrease in the levels of proteins and minerals that are essential for humans, including iron and zinc. Estimates of the potential health impact of these declines, for the current century, range from 138 million to 1.4 billion, depending on the nutrient. Changes in plant-based vitamin content in response to rising CO₂ atmospheric concentrations have not been elucidated, however. The inclusion of vitamin information would improve substantially estimates of health risks. Rice is the primary foods source among crop species for more the 2 billion people. Experiments for 18 rice lines that were genetically diverse, which included Japonica, Indica, and hybrids that are currently grown throughout Asia, were involved in this study that used multiyear, multilocation in situ FACE (free-air CO₂ enrichment). This is the first study to report the integrated nutritional impact of those changes, protein, micronutrients, and vitamins, for the first 10 countries that consume the most rice as part of their daily caloric supply. The declines in protein, iron and zinc were confirmed by the results of this study, as well as finding declines in vitamins B1, B2, B5 and B9, and conversely, an increase of vitamin E. A strong correlation between the impacts of elevated CO₂ on the content of vitamins based on the molecular fraction of nitrogen within the vitamin was observed. Finally, the potential health risks that are associated with the deficits in protein, minerals and vitamins that are present in rice were correlated to the lowest overall gross domestic product per capita for the countries using the most rice, which suggests potential consequences for a global population of approximately 600 million.

Food security is expected to be one of the consequential impacts of increasing atmospheric concentration of CO₂ and climate change (Smith et al., 2014). Impacts that are expected are on the food supply of the global population, in part, due to their vulnerability: up to 1 billion people have been deemed to be food insecure, depending on the definition used (Barrett, 2010). E.g., staple cereal crop harvests, such as rice and maize, could possibly decline by 20% to 40% as a function of surface temperature increase in tropical and subtropical regions by 2100 when not considering the impacts of extreme weather and climate events (Battisti, 2009). There has been an overall direct effort to understand the consequences of atmospheric CO₂ and climate on agricultural production (Schlenker & Roberts, 2009 Lobell, 2008).

The connection between food security and wellbeing, however, extends beyond production per se; e.g., there is a substantial influence of dietary quality on the health of humans (Murray et al., 2013). Insufficient micronutrients, protein, vitamins, etc. van contribute to nutritional deficiencies globally among 2 billion people in developing and developed countries (Baily, West & Black, 2015).  The effects these deficiencies can have directly, such as cognitive development, metabolism, and immune system, and indirectly, obesity and Type 2 diabetes mellitus, affect human health on a panoptic scale (Stein, 2009).

The balance between carbon, which is obtained from atmospheric CO2, and the remaining nutrients, obtained from the soil is a reflection of the chemical composition of a plant (i.e., its ionome). For most plants, as evidenced by more than 100 individual studies as well as several meta-analyses, projected increases of atmospheric CO₂ can result in an ionomic imbalance, where carbon increases disproportionally to nutrients that are soil based (Taub, Miller & Allen, 2008; Loladze, 2014; Myers et al., 2014). Significant consequences for human health can accrue from this imbalance (Myers et al., 2015; Smith, Golden & Myers, 2017) that includes protein and micronutrients. At present, however, there is no information available in regards to a key constituent of nutrition, vitamin content; as a result of this there has not been an integrated assessment (protein, micronutrients and vitamins) available.

Where the diversity of food is limited, i.e. where populations rely heavily on a single plant-based food source, the consequences of qualitative changes that are induced by CO₂ may be exacerbated. According to Zhu et al. in this regard, about 25 % of all global calories is supplied by rice, with the percentage of rice being consumed depending of socioeconomic status, particularly in Asia (McLean et al., 2002). Rice is considered to be among the most important caloric and nutritional sources, particularly in low- and middle-income Asian countries (Kennedy, Burlingame & Nguyen2013).

For those populations that highly dependent on rice, therefore, any change in the integrated nutritional value of rice grains that is induced by CO₂ could affect health disproportionately. Multilocation, multiyear, multivarietal evaluation of rice lines that are widely grown at ambient and anticipated end of century CO₂ to:

1)    Quantify varietal response to changes in components of the diet, such as calcium, iron, protein, zinc, vitamin E, and the vitamin B complex, and

2)    Calculate socioeconomically any deficits that are induced by CO₂ in these nutritional parameters for the 10 countries that are most dependent on rice globally, as a function of domestic product (GDP) per capita.

Though the projections for end-of-century atmospheric concentrations of CO₂ vary, it is very likely that actual atmospheric CO₂ will reach 550 μmol/mol before the end of this century (IPCC, Climate Change, 2014). It is expected that global CO₂ will reach these levels even as additional steps are taken to decrease emissions, partially due to the projected energy usage, the longevity in the atmosphere of the CO₂ molecule, and the temporal delay in reducing CO₂ emissions before the middle of the century (Fischer et al., 2007). Overall, the concentrations used in experiments in this study for elevated atmospheric treatment, 568 to 590 μmol/mol  CO₂ reflect the reality that those born today will be eating rice at CO₂ concentrations of 550 μmol/mol, or higher, within their lifetimes.

Discussion

Approximately 600 million individuals, mostly in countries in Southeast Asia, such as Bangladesh, Cambodia, Indonesia, Lao People’s Democratic Republic (PDR), Madagascar, Myanmar (Burma), and Vietnam, consume ≥50% of their dietary energy per capita and/or their protein from rice directly (FAO, 2016; Seck et al., 2012). The data obtained by this study provides the first integrated assessment of changes induced by CO₂ atmospheric concentration in nutritional quality, protein, minerals and vitamins, for many of the most widely grown lines of rice; as such, they indicate that the atmospheric concentration that is likely to occur this century will add to nutritional deficits for a large segment of the global population.

According to Zhu et al. when assessing the outcome of dietary changes that are induced by atmospheric CO₂ for rice in the current study it is evident that most of these changes, as well as the greatest degree of risk, will occur among the countries with the lowest GDP and the highest dependence on rice. As income increases, however, consumers prefer caloric sources that are more diverse, putting a greater emphasis on protein from fish, dairy, and meat as per western foods (Drewnowski & Popkin, 1997). Future economic development could, therefore, limit CO₂-induced changes in rice nutrition. E.g.., rice accounted for 62% of the total food energy consumption in Japan in 1959, though that fell to 40% in 1976 and, in recent years it fell to less than 20% in 1975 (Choi, Dyck & Childs, 2016). It cannot, however, be assumed there will be strong, sustained economic growth for all countries dependent on rice. In Bangladesh, e.g., in 1990 75% of the total caloric supply per capita came from rice; it was 70% 23 years later in 2013 (http://faostat.fao.Org/beta/en/#data/FBS); while in Madagascar the dependence on rice has increased since 1990 (FAO, 2016). Also, some other countries, such as Guinea, Senegal, and Côte d’Ivoire, have become more reliant on rice as a percentage of the caloric intake (20 – 40% as of 2011) (GRISP (Global Rice Science Partnership), 2013). Overall, though it is likely the top rice-consuming countries will change in the coming decades, globally, the reliance on rice as a dietary staple will continue.

It is also difficult to forecast specific outcomes of consuming rice with reduced nutritional quality. Rice and other staple foods are available widely and affordable for most of the population of the world, the poor in particular. It is understood that undernutrition can put people at risk in countries with low incomes for a wide range of other adverse health outcomes, particularly stunting, diarrheal disease, and malaria (King, Burgess, Quinn & Osei, Eds., 2015). Kennedy et al. (Kennedy, Burlingame & Nguyen, 2013) found, e.g., that the children less than 5 years of age who suffer from stunting, wasting, or are underweight are, in general, high  in countries with generally high per capita consumption of rice. The current data, overall, suggest that for these countries, any change in nutritional quality that is induced by CO₂ would be likely to exacerbate the overall burden of disease and could affect early childhood development.

Without a great deal more socioeconomic data at the country level, which is often not available, it is difficult to provide exact evidence of nutritional deficits, for protein, minerals and vitamins, as well as associated health consequences that are likely to occur in populations that are rice-dependent. Yet, reductions in these qualities that are induced by CO₂ and associated risks of undernutrition are likely to transcend the entire food chain, from harvest to consumption, especially for the poorest people in a country or region.

Cultivar selection, through either traditional breeding or genetic modification, to provide rice that is nutritionally superior with additional CO₂ is an obvious strategy for reducing or negating this risk. For a set of rice lines that are genetically diverse the current data suggest that, for some characteristics (e.g. for protein and vitamin B2) at least, many additional lines would need to be screened; also, it can take many years at present, even decades, to identify, cultivate and distribute new cereal lines that are adapted to a climate that is changing (Challinor et al., 2016). Also, other aspects of a changing climate, especially temperature, would need to be considered. It is indicated by previous work, e.g., that the concentration of protein in rice can be reduced by increasing temperature per se (Ziska et al., 1997). Zhu et al. say that temperature and atmospheric CO₂ concentrations should also be evaluated concurrently regarding the rice nutritional impacts in future assessments, though the extent of future surface temperatures would vary depending on location.

Also, application of mineral fertilisers or postharvest fortification could be included in management. Education about the role of rising atmospheric CO₂ on nutrition, on the consumer side, about the role of rising atmospheric CO₂ on nutrition, which includes opportunities to implement favourable nutrition practices and fortification of food, may also provide opportunities to maintain nutritional integrity. Finally, there is an obvious need for the research community, which includes agronomists, physiologists, nutritionists, and providers of healthcare, to quantify accurately the exact nature of the changes induced by atmospheric CO₂ in the status of human nutrition and their associated health outcomes.

According to Zhu et al. this study provides the first evidence that the anticipated atmospheric CO₂ concentration will result in reductions in integrated quality of rice, which includes proteins, vitamin B, and minerals, for a set of rice lines that are widely grown and genetically diverse. Zhu et al. suggest the occurrence of these nutritional deficits will most likely affect the poorest countries that are the most rice dependent. Overall, it is indicated by these results that the role of rising CO₂ concentrations on the reduction of the quality of rice may represent a fundamental, though underappreciated, human health effect associated with anthropogenic climate change.

Sources & Further reading

1. Zhu, C., et al. (2018). "Carbon dioxide (CO₂) levels this century will alter the protein, micronutrients, and vitamin content of rice grains with potential health consequences for the poorest rice-dependent countries." Science Advances 4(5).