A recent study published in Nature Communications examines how diet, blood glucose levels, and cancer prevalence are related across various vertebrate species. The research provides new insights into the biological factors that influence cancer risk, particularly in birds, which have high blood glucose levels but low cancer mortality rates.
High Blood Sugar and Cancer in Birds
In humans and species with similar glucose metabolism, elevated blood sugar can lead to oxidative stress, DNA damage, protein glycation, and inflammation—factors known to increase cancer risk. However, birds show a unique metabolic pattern.
Unlike mammals, many bird species lack glucose transporter 4 (GLUT4), a protein that facilitates glucose uptake into cells. This difference means birds rely more on fatty acids for energy rather than glucose. As a result, they maintain higher blood glucose levels while having lower cancer incidence compared to mammals and reptiles.
Interestingly, an increase in blood glucose levels has been linked to higher reproductive output in birds, as they tend to produce larger clutches. Despite this association, birds remain the vertebrate group with the lowest cancer mortality rates.
Study Overview
The study analyzed the connection between diet, blood glucose levels, and cancer occurrence across vertebrates. Researchers classified diet into four categories: herbivores, invertivores, primary carnivores, and secondary carnivores. They also assessed the percentage of different food types, including fruits, invertebrates, plants, seeds, and various animal products.
Blood Glucose Variations Across Species
The study found significant differences in blood glucose levels among vertebrates. The Burmese python had the lowest recorded level at 1.2 mmol/L, while the blue-bellied roller bird had the highest at 21.1 mmol/L.
Among vertebrate groups:
Amphibians had the lowest average blood glucose levels (2 mmol/L).
Birds had the highest average (15 mmol/L).
Mammals had a mean level of 6.7 mmol/L.
However, researchers found no clear correlation between dietary habits and blood glucose levels. The proportion of plant-based or animal-based foods consumed did not significantly impact glucose concentrations. Carnivores, herbivores, and omnivores showed similar blood sugar levels despite differences in diet.
Blood Glucose and Cancer Risk
Contrary to expectations, blood glucose levels did not predict cancer risk in vertebrates. When adjusted for factors such as body mass, lifespan, pregnancy length, domestication, and trophic level, glucose levels had no significant effect on cancer prevalence.
Instead, the most reliable predictors of cancer were domestication and trophic level. Domesticated animals, particularly primary carnivores, had a higher cancer risk. However, after accounting for differences in blood glucose levels, this association weakened.
Why Primary Carnivores Have Higher Cancer Risk
Primary carnivores showed a greater likelihood of developing cancer than herbivores, even after adjusting for domestication. Several factors may contribute to this trend:
Toxin Accumulation: Carnivores ingest harmful compounds as they consume prey, leading to higher toxin levels in their bodies.
Oxidative Stress: A meat-heavy diet can cause increased oxidative damage and DNA mutations.
Genetic Diversity Reduction: Domesticated carnivores experience reduced genetic variation, limiting their ability to evolve defenses against cancer.
Interestingly, domesticated bovines had lower blood glucose levels than their wild counterparts, which may make them more vulnerable to cancer.
Study Limitations and Future Research
The study had some limitations. Researchers were unable to track individual glucose levels over time, which made it difficult to determine long-term effects. Blood glucose can also fluctuate due to health status, stress, and diet at the time of collection. Additionally, the study included a limited number of species, though larger cancer mortality databases, such as Species360, could help refine future findings.
Further research is needed to understand why birds have such low cancer rates despite their high blood glucose levels. These insights could contribute to better cancer prevention strategies in humans.
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