Climate change and other factors such as topsoil erosion, land management practices, and agricultural methods affect availability of food crops and potentially impact their associated nutrient levels.1-6 Recent research notes that atmospheric carbon dioxide (eCO2) levels may contribute to the fluctuation of nutrient availability in soil and nutrient uptake by crops, as well as the resulting levels of minerals and proteins in those plants that are ultimately consumed by people.2,5,7,8 The climate-related mechanisms for declines in plant mineral composition are not completely understood, and the argument is made that eCO2 potentially enhances overall crop yield, which may be a benefit in some situations, even if the mineral quality of the crop is decreased.2
When considered through a nutritional lens, the human body requires certain levels of these micronutrients for normal body processes, and deficiencies in one or more micronutrients may lead to detrimental health issues and chronic disease. Already, several nutrient shortfalls have been noted within the US population, most people in the US do not consume the recommended amounts of fruits and vegetables per day, and analysis of National Health and Nutrition Examination Surveys (NHANES) suggests that an estimated 31% of Americans are at risk of developing micronutrient malnutrition.9-11 Several factors may contribute to mineral deficiency, including dietary patterns and the prevalence of a Western-style diet consisting of more processed foods and less vegetables. Additionally, declining nutrient density of food crops has the potential to exacerbate micronutrient malnutrition on a global scale, as well as in our own backyard.
A Focus on Soil
Soil is made up of organic material in addition to particles of minerals and rock, liquids, and gases. An important indicator of soil health is soil respiration, which is essentially a measure of carbon dioxide (CO2) released from the soil due to the decomposition of organic matter by microbes within the soil and the respiration of plant roots and fauna.12 This measurement indicates the level of soil microbial activity, the nutrients available in the soil for uptake by crops, and the soil’s ability to sustain plant growth.12 Essential soil respiration rates depend on factors such as the amount and quality of soil organic matter, temperature, salinity, pH, the circulation of air, and moisture.12
Maintaining a diverse soil biota is essential for agricultural sustainability for both productive and nutrient-dense crop yields.13
In 2016, a government report on US soils suggested that land-use changes in the past 50 years have contributed to reduced ecosystem functions.6 When combined with intensive agricultural practices and soil contamination, this has the potential to reduce soil microbial abundance and impair other functions such as decomposition and nutrient retention.6 In addition, a 2017 European Environment Agency report indicated that effects of climate change have been seen globally and in European soil, with moisture levels significantly decreased in some regions and increased in other regions since the 1950s.14 Climate factors can also affect the level and availability of nutrients such as nitrogen, phosphorus, potassium, and iron in the soil.2 One consideration is that warming air temperatures and increased solar radiation may lead to higher soil temperatures, resulting in more microbial activity, higher soil respiration rates, and potential limitations in soil nutrient availability.6
Affecting the Nutritional Value of Crops
The soil provides many nutrients that plants and humans require, creating a link between soil health and human health. As an example, soil can become acidic for a variety of reasons, including repeated harvesting of high-yielding crops, and the resulting magnesium deficiency negatively affects soil conditions, the sustainability of crop production,15 and potentially the amount of magnesium available when the crop is consumed. A 2020 meta-analysis of 99 field research articles that studied effects of magnesium fertilization on crop production suggested that the magnesium supplementation directly affected the levels of magnesium accumulated in the plant leaf tissues, with an increase of 34.3% on average.15 Continuing research suggests that crops grown on soils containing all the major nutrients for plants often have higher yields and higher nutrient concentrations; however, whether this is true for all types of crops and what soil factors and management techniques yield the most nutrient-dense crops is not well understood.1
Nutrient Deficiencies and Climate Change – From Crops to People
Research has suggested that the nutrient content of crops has declined over the years, possibly in part due to a number of factors such as the cultivated plant varieties, land and soil management practices, and climate change.2,8,16,17 A 2014 meta-analysis of 7,761 observations, including 2,264 observations at free air CO2 enrichment (FACE) centers and including 130 species, suggested that elevated CO2 levels reduced the overall concentration of 25 minerals in plants, including calcium, potassium, zinc, and iron, by 8% on average.8 In addition, this increased CO2 exposure increased the ratio of carbohydrates to minerals in the studied plants.8 A 2017 review found that elevated CO2 concentrations potentially resulted in a 3-11% decrease in zinc and iron in cereal grains and legumes, specifically.5 In addition to minerals, elevated eCO2 potentially impacts the protein concentration of various grains, which may significantly affect countries that rely on grain crops as sources of dietary protein.2,18,19
With increasing global warming concerns and continued micronutrient malnutrition worldwide, an emphasis on climate factors and how they impact nutrients in important food crops has surfaced in current research. Health organizations have reported on micronutrient malnutrition, including iodine, iron, folate, vitamin A, and zinc, that continues to have devastating consequences for billions of people across the globe.20-25 Micronutrient malnutrition has been associated with a wide range of physiological impairments, including metabolic disorders; reduced immune, endocrine, and cognitive function; and delayed or inadequate physical development.11,21,23 Magnesium, for example, is present in a variety of crop foods, from greens to whole grains. Yet this essential micronutrient is under-consumed in the US,9,26-28 with studies indicating that low intake may be associated with a greater risk for several chronic diseases.27,29
Elevated Atmospheric CO2 – VegETABLEs, Grains, Minerals, and Protein
Increased levels of eCO2 potentially increase the yield of various crops through the enhancement of their photosynthetic rates.2,30 However, the impact on nutritional quality of those crops is an important consideration in the scope of micronutrient malnutrition concerns. A 2018 meta-analysis that used 57 articles consisting of 1,015 observations found that eCO2 increased the concentrations of sugars, antioxidant capacity, phenols, flavonoids, ascorbic acid, and calcium in the edible part of vegetables, but decreased the concentrations of protein, nitrate, magnesium, iron, and zinc at the following noted percentages:30
- Decreases in magnesium concentrations were at 9.2%.
- Decreases in zinc concentrations were at 18.1% in both fruit and root vegetables and 10.7% in stem vegetables.
- Decreases in iron concentrations were greatest in leafy vegetables at 31%, followed by fruit vegetables (19.2%) and root vegetables (8.2%).
Elevated eCO2 is also a potential factor for decreased minerals and proteins in C3 grasses and legumes, which include cereal grains such as wheat, rice, barley, and oats.2,18,19,30 An often cited 2014 meta-analysis investigated 143 comparisons of six food crops grown at ambient and increased CO2 levels.19 The experiments had been conducted from seven different FACE experimental locations and tested the nutrient concentrations of the edible portions of rice, wheat, maize, soybeans, field peas, and sorghum.19 Meta-analysis results suggested the following:19
- Higher CO2 levels are associated with significant decreases in the concentrations of zinc and iron in all C3 grasses and legumes.
- At higher CO2 levels, wheat grains showed 9.3% lower zinc and 5.1% lower iron.
- At higher CO2 levels, C3 grasses showed lower protein levels with a 6.3% decrease in wheat grains and a 7.8% decrease in rice grains.
Food crops: Organic vs Nonorganic
Longitudinal studies have suggested more positive outcomes for patients’ health and wellness when an organic diet is consumed compared to a conventional dietary pattern. For example, following an organic diet, including organic dairy, eggs, meats, and plants, may potentially increase intake of omega-3 fatty acids, reduce risk of allergic disease and obesity, and reduce exposures to food treated with antibiotics, to fungal toxins, and to toxic metals.31,32 Specifically for the consumption of organic versus conventionally grown food crops, study results may not be conclusive due to confounding variables such as overall lifestyle.31,32 According to a recent systematic review, few clinical trials have tested direct health improvements associated with organic food crop consumption, and have more often been indirect, assessing health outcomes based on differences in pesticide exposure.32
While lower pesticide residues among organic crops leads to the health benefit of lower toxicant exposure, differences in the actual composition of organic versus conventional crops may be limited.31 According to compiled systematic reviews and meta-analyses, results suggest that while the overall mineral and vitamin levels in plants may not be significantly impacted by the method of crop production,31 higher content levels of polyphenolic compounds in organic food crops have been shown.31,33 Many of these compounds have been associated with reducing the risk of a wide range of chronic diseases. A 2014 systematic review and meta-analysis of 343 peer-reviewed publications found that concentrations of antioxidants such as polyphenols were much higher in organic crops and organic crop–based foods.33 Specifically, the analysis found the following chemicals and estimated percentages:33
- Phenolic acids – 19% higher concentration in organic crops
- Flavanones – 69% higher concentration in organic crops
- Stilbenes – 28% higher concentration in organic crops
- Flavones – 26% higher concentration in organic crops
- Flavonols – 50% higher concentration in organic crops
- Anthocyanins – 51% higher concentration in organic crops
Research investigations have presented compelling results regarding fluctuating nutrient levels in food crops. Within the scope of micronutrient malnutrition in the United States and worldwide, these scientific results and conclusions are important to consider for the prevention of chronic diseases and the promotion of optimal health for the global population. Various shortcomings, variables, and gaps are evident in the research literature as the scientific and medical communities attempt to fully understand the relationship between the environment, agriculture, food consumption, and human health. One scientific article summarized contextual concerns and suggested that:34
- Archived samples of soil that had been cultivated to a great extent, yet managed with fertilizer treatments, showed no decline in mineral density.
- Crop varieties, sampling methods, and laboratory and statistical analyses have changed over the years and may impact comparative study results.
- Vegetables and fruits remain broadly nutrient dense, adequate nutrition is accessible through eating recommended serving amounts, and the increased food crop yields for a growing population outweighs potential nutrient dilution effects.
The impact of elevated levels of CO2 on all essential micronutrients is not well represented in research, and recent reviews also suggest that the climate-related mechanisms for noted declines in plant mineral composition are not well understood, nor are the soil factors or management techniques that would yield the most nutrient-dense crops.1,2 Finally, weighing the potential benefits of eCO2 on crop yields against potential impact on nutritional composition of crops and translating those conclusions to direct human health consequences is an ongoing debate.
Functional Medicine Considerations
Understanding the evolving relationship between environmental factors, food crops, and human health enhances clinical awareness to ultimately move patients to better health and well-being. Nutrient density decline in some food crops, especially in the context of micronutrient malnutrition, is an important clinical consideration due to nutrient shortfalls that have already been seen within the US population and due to reports that most Americans do not consume the recommended amounts of fruits and vegetables.
Assessment of micronutrient deficiencies or risk of deficiency is essential during clinical intake to determine underlying causes of chronic symptoms or conditions, and addressing these deficiencies has the potential to improve or resolve many health issues. Evaluating potential toxicant exposure through food crops is another clinical consideration. Within the Functional Medicine Model, a comprehensive view of a patient’s historical and current conditions, including nutrition intake and dietary patterns, helps to determine appropriate interventions for each individual patient. Micronutrient malnutrition can be detrimental for a patient’s health, and those deficiencies may not be immediately obvious. Assessment tools such as the nutrition-oriented physical exam help detect imbalances by performing the physical exam through a nutritional lens. In addition, nutrition intake assessments and food diaries help determine amounts of nutrients consumed, help evaluate the variety of food choices, and may help inform treatment strategy.
Any decline of essential micronutrients in food crops is important to consider for the potential prevention of health issues, including chronic diseases, as well as for the promotion of optimal health for patients. Learn more about the impact of modern food production practices through the Food for Health: Critical Choices & Food Ecology eLecture bundle. Expert clinicians explore the effects of nutrition on many chronic conditions and how environmental stressors contribute to overall dysfunction. AIC 2020 conference proceedings are available with eligible CME credit.
- Fischer S, Hilger T, Piepho HP, et al. Soil and farm management effects on yield and nutrient concentrations on food crops in East Africa. Sci Total Environ. 2020;716:137078. doi:10.1016/j.scitotenv.2020.137078
- Soares JC, Santos CS, Carvalho SMP, Pintado MM, Vasconcelos MW. Preserving the nutritional quality of crop plants under a changing climate: importance and strategies. Plant Soil. 2019;443:1-26. doi:10.1007/s11104-019-04229-0
- Bashagaluke JB, Logah V, Opoku A, Sarkodie-Addo J, Quansah C. Soil nutrient loss through erosion: impact of different cropping systems and soil amendments in Ghana. PLoS One. 2018;13(12):e0208250. doi:10.1371/journal.pone.0208250
- Fanzo J, Davis C, McLaren R, Choufani J. The effect of climate change across food systems: implications for nutrition outcomes. Glob Food Sec. 2018;18:12-19. doi:10.1016/j.gfs.2018.06.001
- Myers SS, Smith MR, Guth S, et al. Climate change and global food systems: potential impacts on food security and undernutrition. Annu Rev Public Health. 2017;38:259-277. doi:10.1146/annurev-publhealth-031816-044356
- Subcommittee on Ecological Systems, Committee on Environment, Natural Resources, and Sustainability of the National Science and Technology Council. The state and future of US soils: framework for a federal strategic plan for soil science. Published December 2016. Accessed May 20, 2020. https://obamawhitehouse.archives.gov/sites/default/files/microsites/ostp/ssiwg_framework_december_2016.pdf
- Jin J, Armstrong R, Tang C. Impact of elevated CO2 on grain nutrient concentration varies with crops and soils – a long-term FACE study. Sci Total Environ. 2019;651(Pt 2):2641-2647. doi:10.1016/j.scitotenv.2018.10.170
- Loladze I. Hidden shift of the ionome of plants exposed to elevated CO2 depletes minerals at the base of human nutrition. eLife. 2014;3:e02245. doi:10.7554/eLife.02245
- US Department of Health and Human Services and US Department of Agriculture. 2015–2020 Dietary Guidelines for Americans. 8th ed. USDA/HHS; 2015. Accessed May 20, 2020. http://health.gov/dietaryguidelines/2015/guidelines
- Only 1 in 10 adults get enough fruits or vegetables. Centers for Disease Control and Prevention. Published November 16, 2017. Accessed May 20, 2020. https://www.cdc.gov/media/releases/2017/p1116-fruit-vegetable-consumption.html
- Bird JK, Murphy RA, Ciappio ED, McBurney MI. Risk of deficiency in multiple concurrent micronutrients in children and adults in the United States. Nutrients. 2017;9(7):655. doi:10.3390/nu9070655
- United States Department of Agriculture – Natural Resources Conservation Service. Soil respiration. Accessed May 20, 2020. https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_053267.pdf
- Hendgen M, Hoppe B, Doring J, et al. Effects of different management regimes on microbial biodiversity in vineyard soils. Sci Rep. 2018;8(1):9393. doi:10.1038/s41598-018-27743-0
- European Environment Agency. Soil, land and climate change. Modified December 20, 2019. Accessed May 20, 2020. https://www.eea.europa.eu/signals/signals-2019-content-list/articles/soil-land-and-climate-change
- Wang Z, Hassan MU, Nadeem F, Wu L, Zhang F, Li X. Magnesium fertilization improves crop yield in most production systems: a meta-analysis. Front Plant Sci. 2020;10:1727. doi:10.3389/fpls.2019.01727
- Davis DR, Epp MD, Riordan HD. Changes in USDA food composition data for 43 garden crops, 1950 to 1999. J Am Coll Nutr. 2004;23(6):669-682. doi:10.1080/07315724.2004.10719409
- Davis DR. Declining fruit and vegetable nutrient composition: what is the evidence? HortScience. 2009;44(1):15-19. doi:10.21273/HORTSCI.44.1.15
- Medek DE, Schwartz J, Myers SS. Estimated effects of future atmospheric CO2 concentrations on protein intake and the risk of protein deficiency by country and region. Environ Health Perspect. 2017;125(8):087002. doi:10.1289/EHP41
- Myers SS, Zanobetti A, Kloog I, et al. Increasing CO2 threatens human nutrition [published correction appears in Nature. 2019;574(7778):E14]. Nature. 2014;510(7503):139-142. doi:10.1038/nature13179
- Vitamin and mineral nutrition information system (VMNIS): micronutrient database. World Health Organization. Accessed May 20, 2020. https://www.who.int/vmnis/database/en
- Allen L, de Benoist B, Dary O, Hurrell R, eds. Guidelines on Food Fortification With Micronutrients. World Health Organization and Food and Agricultural Organization of the United Nations; 2006. Accessed May 20, 2020. https://apps.who.int/iris/bitstream/handle/10665/43412/9241594012_eng.pdf
- Thompson B, Amoroso L, eds. Combating Micronutrient Deficiencies: Food-Based Approaches. CAB International and Food and Agricultural Organization of the United Nations (FAO); 2011. Accessed May 20, 2020. http://www.fao.org/3/a-am027e.pdf
- Baily RL, West KP Jr, Black RE. The epidemiology of global micronutrient deficiencies. Ann Nutr Metab. 2015;66(suppl 2):22-33. doi:10.1159/000371618.
- Ritchie H, Roser M. Micronutrient deficiency. Our World in Data. Published August 2017. Accessed May 20, 2020. https://ourworldindata.org/micronutrient-deficiency
- Centers for Disease Control and Prevention. Nutrition: micronutrient facts. Reviewed March 9, 2020. Accessed May 20, 2020. https://www.cdc.gov/nutrition/micronutrient-malnutrition/micronutrients/index.html
- Marriott BP, Olsho L, Hadden L, Connor P. Intake of added sugars and selected nutrients in the United States, National Health and Nutrition Examination Survey (NHANES) 2003-2006. Crit Rev Food Sci Nutr. 2010;50(3):228-258. doi:10.1080/10408391003626223.
- Drake VJ. Micronutrient inadequacies in the US population: an overview. Linus Pauling Institute, Oregon State University. Published November 2017. Accessed May 20, 2020. https://lpi.oregonstate.edu/mic/micronutrient-inadequacies/overview
- What we eat in America, NHANES 2011-2012. Table 37: total nutrient intakes. US Department of Agriculture, Agricultural Research Service. Published 2014. Accessed May 20, 2020. https://www.ars.usda.gov/ARSUserFiles/80400530/pdf/1112/Table_37_SUP_GEN_11.pdf
- Rosanoff A, Dai Q, Shapses SA. Essential nutrient interactions: does low or suboptimal magnesium status interact with vitamin D and/or calcium status? Adv Nutr. 2016;7(1):25-43. doi:10.3945/an.115.008631
- Dong J, Gruda N, Lam SK, Li X, Duan Z. Effects of elevated CO2 on nutritional quality of vegetables: a review. Front Plant Sci. 2018;9:924. doi:10.3389/fpls.2018.00924
- Mie A, Andersen HR, Gunnarsson S, et al. Human health implications of organic food and organic agriculture: a comprehensive review. Environ Health. 2017;16(1):111. doi:10.1186/s12940-017-0315-4
- Vigar V, Myers S, Oliver C, Arellano J, Robinson S, Leifert C. A systematic review of organic versus conventional food consumption: is there a measurable benefit on human health? Nutrients. 2019;12(1):7. doi:10.3390/nu12010007
- Bara?ski M, Srednicka-Tober D, Volakakis N, et al. Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature review and meta-analyses. Br J Nutr. 2014;112(5):794-811. doi:10.1017/S0007114514001366
- Marles RJ. Mineral nutrient composition of vegetables, fruits and grains: the context of reports of apparent historical declines. J Food Compost Anal. 2017;56:93-103. doi:10.1016/j.jfca.2016.11.012