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aging

aging

Introduction

  • the biologic factors causing mammalian aging process is still poorly understood
  • aging is one of the most common risk factors for human disease

why do we age?

  • the rate of ageing varies substantially across different species, and this is mainly genetically based and the biological mechanisms which regulate lifespan evolved several hundred million years ago
  • genetic traits that benefit early survival and reproduction will be selected for in evolution even if they contribute to an earlier death
  • ageing thus results from a combination of:
    • programmed genetic factors
    • acquired damage factors including injuries, wear and tear, environmental exposures, disease, free radicals, etc
    • habit factors - to a certain extent, we become what out habits make us become
    • vicious cycles causing spiraling decline eg. damage may cause disabling injury which reduces mobility which reduces muscle mass and cardiovascular fitness and potentially causing obesity, all of which can contribute to cardiovascular disease, osteoporosis, frailty and cognitive decline
  • suggested metabolic pathways:
    • the FOXO3/Sirtuin pathway, probably responsive to caloric restriction
    • the activity levels of the electron transport chain in mitochondria
      • studies have suggested a key role for decreasing NAD levels as a causative factor
        • taking eNAMPT from the blood of young mice and transferring it to older mice increased their life span by 16% and their life span correlated well with the serum levels of NAD
        • adipose tissues release eNAMPT into extracellular vesicles which are transported to the hypothalamus which then creates NAD and appears to be critical in the aging process 1)

normal ageing

  • reduced hearing
    • this begins in teenage years with gradual loss of high frequency perception
    • presbycusis inhibiting speech perception occurs in over half of those over 75yrs - mammals have genetically lost the ability to regenerate cochlear sensorineural cells in the way that fish, amphibians and birds do
  • reduced vision
    • presbyopia - inability to focus as close - this is most commonly evident from age 45yrs
    • over half of those over age 80yrs will have cataracts
    • macular degeneration is increasingly a problem in those over 80yrs
  • reduced soft tissue collagen
    • skin
  • reduced flexibility of joints
  • reduced muscle mass, balance and coordination leading to frailty and falls
  • UV induced skin ageing - keratoses, wrinkles, skin cancer
  • graying of hair
  • reduced cognition
    • peaks in mid-20's
    • dementia becomes more common with age
  • reduced female fertility culminating in menopause
  • reduced dentition
  • increased DNA methylation levels
  • increased risk of neoplasia / cancer / tumours
aging.txt · Last modified: 2019/06/18 00:50 (external edit)