This is one of the findings in a study of the aging process and metabolic rates related to mitochondrial physiology by Dr Tony Hickey from the Applied Surgery and Metabolic Physiology Group at the University of Auckland.
In this study, Dr Hickey looked at the aging process in birds to understand the impact their metabolic rate has on aging. He recently outlined progress in this study.
Human Life Expectancy
Humans are a long-lived species with a maximum life span expectancy of around 122 years. Life expectancy is higher in females and increasing at the rate of two years every decade. Despite this long life-span, sickness tends to affect people at around the same age, such as cancers in the mid to late 50s.
Many birds are long-lived, relative to their mass. For example parrots are known to live at least 96 years and can possibly live to 120+ years. Some species of seabirds are known to live 80-90 years, raptors 70-80 years and even sparrows can live for 15-24 years. The most remarkable bird, given its high metabolic rate, is the hummingbird, which weighs just 5mg but is known to live for up to 14 years.
Bird Life Span Under Rapid Selection
This type of aging is driven by selection for rapid and sustained growth. Birds are longer lived relative to their body mass. A bird’s metabolic rate is higher due to adaptations for flight and birds exhibit differences in senescence, cell division, metabolism and flight.
For example, the measured life span (MLSP) and basal metabolic rate of a Macaw is 11/97, giving a ratio of 8.36, while a human MLSP is 27/122 giving a ratio of 4.52.There are a number of reasons for this difference. In terms of oxidative stress and mitochondrial activity, birds run hot at 42 degrees celsius and also have more saturated membrane lipids, compared to humans at 37 degrees celsius.
Exercise Improves Mitochondrial Structure
When looking at exercise capacity and improved and normal muscle mass, it is known that COX is a mitochondrial enzyme that is elevated with exercise. This causes mutations in mitochondria to decrease, so exercise improves the structure of mitochondria.
“Our data clearly supports endurance exercise as a medicine and a lifestyle approach to improving systemic mitochondrial function,” said Dr Hickey. "Exercise is good for correcting age-related problems", he said. Human athletes tend to live only marginally longer than average, but they tend to have less complications associated with aging.
Evolutionary Changes Benefit Birds
Birds have very high blood glucose, (16mM in birds compared to 5.5mM in mammals), and also have a different blood structure to humans - one that is more efficient at getting ATP out of the blood. Birds have gone to enormous (evolutionary) lengths to lower their body weight and their liver is about one third, proportionally, of the size of mammals. This is one of the many ways they have evolved weight saving for flying.
Birds also have lower levels of insulin and fewer pancreatic beta cells, so their sensitivity to glucose is lower. Levels of glycogen are 5-10 times higher in birds. Calorie restriction results in a release of glycogen into the muscles for storage, and this results in sirtuins that promote aerobicity.
Birds Live Longer With Less Cancer
Telomeres are the DNA on the end of chromosomes that protect the tip of the chromosome from the effects of division. These telomeres are important for longevity, and avian telomeres are 4 - 10 times longer than those in mammals.
Sirtuins are regulated by energy states, particularly a low calorie diet and exercise, which result in a long lifespan and aerobicity. This means that birds should live longer and have a lower incidence of insulin mediated cancers.
High insulin levels, as in type 2 diabetes, are associated with elevated cancer rates in mammals. Studies on birds in zoos have found that birds do have lower cancer rates and tend to have mainly virally mediated cancers. When that is taken into account, the difference in cancer rates is massive.
Eat Less and Exercise More
Eating less lowers insulin levels, and exercise raises glycogen levels. Can this slow the aging process? Endurance exercise, defined as 60 percent of maximal oxygen uptake (VO2 max) maintained for a long time, such as five months, could increase lifespan.
A recent paper in Nature Magazine found that free radicals can be beneficial, in moderation. Anti-oxidants can be detrimental if not given in balance, as they are also intra-cellular messengers or mediators and are necessary to cells.
References
- Hickey, Anthony J.R. and Julia MacDonald, 2010, ‘Simultaneous Measurement of Mitochondrial Respiration and Free Radical Production in Skeletal and Cardiac Muscle Fibres,’ paper given at 2010 Biomedical Conference, Auckland, New Zealand.
- Gustavo Barja, 2004, ‘Aging in Vertebrates, and the Effect of Caloric Restriction: A Mitochondrial Free Radical Production–DNA Damage Mechanism?’, Biol. Rev. (2004), 79, pp. 235–251, Cambridge Philosophical Society.
Dr Tony Hickey, Applied Surgery and Metabolic Physiology Group, University of Auckland - talk at University of Auckland, 21/07/2011.
