A large-scale study of 88 bird species reveals that some birds with high blood sugar levels show resistance to protein glycation, suggesting they have evolved mechanisms to avoid the harmful effects typically associated with glucose metabolism.
The study found that larger birds, such as flamingoes, had lower blood sugar levels and lower rates of glycation than smaller birds. Image credit: Alejandro Contreras via Unsplash
The study is the first extensive, comparative analysis of the relationship between blood sugar levels, glycation rates, diet and life history in birds. Published today as a revised Reviewed Preprint in eLife, it is described by the editors as important work with convincing evidence that blood sugar level is positively correlated with glycation levels. Although there are some limitations related to data collection, they say that these likely make the statistically significant findings more conservative.
Understanding how different species regulate blood sugar levels is essential for uncovering the links between metabolism, ageing and disease. High blood sugar is typically associated with accelerated ageing and health complications, largely due to protein glycation – a process where sugars react with proteins, leading to cellular damage.
The pace-of-life syndrome hypothesis proposes that an organism’s metabolic rate, lifespan, reproductive strategies and behaviour evolve in predictable ways. Under this framework, species with fast metabolisms, short lifespans and high reproductive rates are expected to have higher blood sugar and glycation levels. Conversely, those with longer lifespans and slower developmental times should have lower blood sugar levels and greater resistance to glycation. However, it is unclear how glycation has coevolved with other traits across species, and so it is undetermined whether glycation fits into the framework of the pace of life hypothesis.
“Birds are particularly relevant in this context, given their relatively high blood sugar levels – on average almost twice as high as similarly sized mammals,” says lead author Adrián Moreno-Borrallo, (PhD) at the Institut Pluridisciplinaire Hubert Curien, University of Strasbourg, CNRS, Strasbourg, France. “This is thought to be an adaptation allowing flight, providing birds with the fuel needed to power intense bursts of aerobic exercise. But it is also paradoxical. Despite their higher blood sugar levels, birds show remarkable longevity compared to their mammalian counterparts, living up to three times longer.”
To investigate this apparent paradox, Moreno-Borrallo and colleagues conducted an analysis of 484 individual birds from 88 different species. They compared blood sugar levels and glycation rates in relation to the birds’ life history traits – lifespan, body mass, developmental time, reproductive investment (measured by clutch mass – the total mass of their eggs) and diet. They sought to identify whether these species of birds followed the framework set by the pace-of-life syndrome hypothesis.
Their results revealed substantial variation in blood sugar levels across species. Smaller birds, such as swifts and passerines, had the highest blood sugar levels, while larger species, such as flamingos and geese, had the lowest. Glycation rates followed a similar trend, with smaller birds showing higher levels and larger birds displaying lower levels.
However, the relationship between blood sugar levels and lifespan was more complex. While longer-lived birds generally had higher blood sugar levels, this increase plateaued beyond a certain point. This suggests that some species have evolved mechanisms to prevent glycation-related damage, rather than avoiding high blood sugar levels altogether.
Another unexpected finding was that terrestrial carnivorous birds had significantly higher glycation rates than omnivorous birds, despite having similar blood sugar levels. This indicates that factors beyond blood sugar levels, such as differences in protein metabolism, antioxidant defences or dietary components including fibre and polyunsaturated fatty acids, may influence how different species are able to mitigate glycation-related damage.
The results challenge some predictions of the pace-of-life syndrome hypothesis. While body size showed a strong relation to blood sugar levels, reproductive investment showed no significant relationship with glycation, and glucose levels increased with lifespan instead of decreasing.
“Our results are only in minor agreement with predictions from the pace-of-life syndrome hypothesis. It holds true for body mass, but not for the other life-history variables tested,” says co-senior author Fabrice Bertile, a researcher at the Institut Pluridisciplinaire Hubert Curien, University of Strasbourg, CNRS, and the National Proteomics Infrastructure, ProFi, Strasbourg, France. “The link between blood sugar levels and lifespan may depend on species-specific factors that influence how glucose affects ageing. Further research should target this area, as well as exploring other groups of birds that are underrepresented in our study due to logistical constraints.”
“These results increase our knowledge about the diversity of blood sugar levels and glycation patterns across birds, challenging conventional wisdom about metabolism, ageing and disease,” concludes co-senior author François Criscuolo, a researcher at the Institut Pluridisciplinaire Hubert Curien, University of Strasbourg, CNRS. “There is considerable variation in blood sugar levels and glycation rates between species, with those with the highest glucose levels showing greater resistance to glycation, hinting at an evolved mechanism for this resistance. Understanding how this glycation resistance arose could provide crucial insights in human health research, particularly in areas like diabetes, longevity and metabolic disorders.”
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