Soil Fertility and Human Intelligence: Exploring the Scientific Link

Emerging research connects soil fertility, nutrition, brain development and physical exercise, but scientists are still investigating whether soil quality has any direct influence on human intelligence.

The Soil - Intelligence Connection

Human intelligence is shaped by several interacting factors, including genetics, nutrition, education, health and the environment. A study published in Scientific Reports on November 4, 2025, introduced an intriguing question by examining the relationship between soil fertility and estimated average national intelligence quotient (IQ) across 126 countries. Researchers reported a correlation coefficient of 0.58, with their statistical model accounting for 34 per cent of the variation in national IQ estimates. However, the study established an association rather than causation. It did not directly measure individuals' diets, nutrient absorption or cognitive development, and its findings cannot prove that fertile soil makes people more intelligent.

India's Soil Health and Nutritional Challenges

Soil provides minerals that plants require for growth, but their availability depends on soil chemistry, pH, farming practices and environmental conditions. A nationwide Indian study published in Scientific Reports in 2021 analysed 242,827 agricultural soil samples from 615 districts across 28 states. It identified deficiencies, including latent deficiencies, in sulphur in 58.6 per cent of samples, zinc in 51.2 per cent, boron in 44.7 per cent, iron in 19.2 per cent, manganese in 17.4 per cent and copper in 11.4 per cent. These figures describe agricultural soil conditions, not the percentage of people who lack these nutrients.

Further evidence emerged from a 2023 Indian study that linked more than 27 million soil tests with health data covering nearly 300,000 children and one million adult women. Researchers found associations between soil zinc availability and children's growth, and between soil iron availability and haemoglobin levels. These findings highlight the importance of soil management for nutritional health, although they do not establish a direct relationship between soil minerals and IQ.

From Soil to Food and the Human Brain

The journey from soil to brain involves several stages. Minerals must first be available for plants to absorb, and the harvested crop's nutritional composition depends on its variety, growing conditions and agricultural practices. The nutrients must then be consumed and absorbed by the human body. Iron, iodine and zinc are particularly important for normal development and physiological function. Iron supports oxygen transport and cognitive development, while iodine is essential for thyroid hormones that support the developing brain. Zinc contributes to growth and cellular function. However, food preparation, dietary diversity and digestive health also influence how much nutrition the body receives. Therefore, soil quality alone cannot predict the nutritional value of a meal or an individual's intelligence.

Early Childhood: A Critical Window for Brain Development

Nutrition is particularly important during pregnancy and early childhood, when the brain develops rapidly. The World Health Organization's nurturing-care framework emphasises adequate nutrition, responsive caregiving, safety and early learning opportunities. Deficiencies in iron or iodine during critical developmental periods can have lasting consequences, while inadequate overall nutrition can undermine healthy growth. Research on iron supplementation among school-age children has reported improvements in certain cognitive outcomes, particularly among children who were anaemic at baseline. However, correcting a deficiency does not mean that additional supplements will increase intelligence in adequately nourished children. Education, healthcare, language exposure and a stimulating environment also influence cognitive development.

Modern Agriculture: Fertilisers, Pesticides and Food Safety

Modern agricultural practices support food production, but excessive or unbalanced chemical use can create environmental challenges. Urea supplies nitrogen required for plant growth, yet repeated overapplication can contribute to soil acidification, nutrient imbalances and water pollution. Balanced fertilisation and soil testing are therefore essential for maintaining soil health. Pesticides serve different purposes, including controlling insects, weeds and fungal diseases. Their persistence and potential health effects depend on the chemical, application practices and exposure levels. Some pesticides can harm the nervous system, particularly when exposure is high or occupational safety measures are inadequate. Nevertheless, pesticide-treated food is not automatically nutritionally inferior or unsafe. Evidence linking farming and occupational pesticide exposure with brain cancer does not establish that eating conventionally grown food causes brain tumours.

Food Versus Supplements: What Supports Intelligence?

A varied diet supplies combinations of vitamins, minerals, protein, fibre and other beneficial compounds, while supplements provide selected nutrients in concentrated doses. Supplements can be valuable when correcting deficiencies or addressing inadequate intake, but excessive consumption can be harmful. Too much iron can cause toxicity, excessive zinc can interfere with copper absorption, and excessive iodine or selenium can produce adverse effects. There is no strong evidence that routinely taking additional vitamins or minerals increases IQ in healthy, adequately nourished adults. The Dietary Guidelines for Indians 2024, published by ICMR–National Institute of Nutrition, emphasise dietary diversity and balanced meals containing vegetables, fruits, pulses, whole grains and suitable animal or fortified foods.

Exercise, Brain Training and Cognitive Performance

Physical exercise has stronger direct evidence for improving certain cognitive abilities than the proposed relationship between soil fertility and intelligence. A 2025 umbrella review published in the British Journal of Sports Medicine combined 133 systematic reviews covering 2,724 randomised controlled trials and 258,279 participants. It reported improvements in general cognition, memory and executive function, with standardised mean differences of 0.42, 0.26 and 0.24 respectively. These figures represent statistical effect sizes, not percentage increases in IQ. Exercise supports cardiovascular health and may influence processes involved in learning and neuroplasticity. The World Health Organization recommends adults undertake 150–300 minutes of moderate-intensity aerobic activity weekly, alongside muscle-strengthening activities on at least two days. Mental exercises such as puzzles and memory games can improve practised skills, but evidence that they substantially increase general intelligence remains limited.

Sleep, Age and Lifelong Learning

Sleep supports memory consolidation, attention and learning, while insufficient sleep can impair decision-making and working memory. Nutritional requirements and absorption also change across the lifespan. Pregnancy and early childhood are especially sensitive periods for brain development, while older adults may face increased risks of deficiencies, including vitamin B12 deficiency associated with reduced stomach acid. Calcium absorption also varies with age and physiological needs. These differences reinforce the importance of age-appropriate nutrition, regular physical activity, adequate sleep and continued learning. However, neither age nor any single nutrient determines a person's cognitive abilities.

What Science Still Needs to Establish

The direct influence of soil fertility on human intelligence remains unproven. Future research must connect soil conditions with crop nutrient composition, individual dietary intake, nutritional biomarkers and validated cognitive assessments. It must also account for education, healthcare, socioeconomic circumstances and other environmental influences. For India, combining agricultural soil surveys with nutritional and child-development data could help clarify where soil deficiencies and human nutritional problems overlap. The evidence already supports protecting soil health, preventing nutritional deficiencies, improving early childhood care and encouraging physical activity. Ultimately, human intelligence emerges from multiple interacting influences. Healthy soil can contribute to a healthier food system, but intelligence cannot be reduced to soil fertility, a particular nutrient or a single brain-training exercise.