It is very apparent from nature that living organisms are extremely capable of selecting nutrients that they need and throwing away the ones that are in excess. The body does it without any outside regulation and with ease.  

How many supplements are too many?

The problem of excess nutrients only arises when synthetic chemicals are offered instead of food based concentrates and supplements. These supplements including synthetic vitamins and minerals can correct symptoms of severe deficiency - for example scurvy - Vitamin C deficiency and Beriberi vitamin B1 hypovitaminosis.

However,  synthetic non-food based supplements can create severe excesses and overdoses. Good examples are fat soluble vitamins ADEK or overdoses of minerals in chemically manufactured mineral supplements. I frequently see this in hair testing dogs.

The body is designed to process food based nutrients 

and not chemicals which can easily create a state of excess often expressed in agitation, heat production and digestive problems. These are the main reasons why I only recommend naturally-fermented vitamins,  probiotics, plant-based minerals and naturally sourced omega oils that are powerful, yet gentle and can be managed by the body well.  

A simple example of the difference between taking a cheap synthetic multivitamin that commonly causes stomach upsets when taken on empty stomach and a naturally fermented multivitamin that usually does not cause such symptoms.

Nature never measures the exact amounts of vitamins and nutrients in food. It just provides nutrients that are natural and non-synthetic.

There are two major and very common problems in nutrition and the origin of premature aging and chronic disease:

1. Deficiency of nutrients and vitamins that result from soil and food depletion.

2. Supplementing them in artificial forms. 

It is not a question if supplements are needed but what forms to give and which ones to avoid.

Additional recommended reading:

How many supplements are too many for dogs and which ones to give