Understanding Metabolism Slowdown with Age: Causes & Factors

Question
What causes a person's metabolism to slow down when they get older? It seems to me that when exercising anyway a person should burn the same amount of energy when they do the same amount of work.

Answer
James,

The reasons are multifaceted.  Principle among the reasons is hormonal.  The hormones such as thyroid, growth hormone and gonadal (sex) hormones such as Testosterone in men and the estrogens/progesterone in women play a part in metabolism.  Not only the production of said hormones but also the hormone receptors on each of our cells.  As we age hormone receptors diminish in numbers.  With lower receptor (R) counts, the effects of serum levels of hormones is less than expected.  Other things impact our hormone activity such as SHBG (sex-hormone binding globulin) a necessary protein carrier-protein for hormones t/o the blood stream.  As we age our SHBG rises and there is more bound hormone in circulation.  This bound hormone is inactive.  

Within the cell things happen to slow down metabolism... cell aging and apoptosis.  Absorption of nutrients and release and removal of toxins and metabolic end-products can also affect the rate of metabolism.  When one gets their hormones in order as they age (especially the GH (using IGF-1 blood testing as a barometer) then we can see a "reverse" in our rate of metabolism and use of energy (calories).  There are treatments to uncouple SHBG from hormones as well as supplements and medications to up-regulate (R)-hormone receptors.  All these principles and protocols are the basis of the "anti-aging" or longevity practice of medicine.


Hope this is helpful.