Theory 9 of why we age

Deficiency in various vital molecules

 There are many molecules that diminish in concentration in areas of the body where they are required, especially in mitochondria, “the power house of the cells” where ATP is generated. As we age, science is discovering many processes and substances that diminish with time.  For instance, much lower niacin levels in mitochondria with age lower the ability to make NAD+ that is essential for energy production, making us more fatigued when older.

It is unclear why this is so.  A basic hypothesis is that after we pass reproductive age, our genes become less important, so things simply are not maintained well.

Specific molecules are listed in How to slow these aging processes