QUICKLINKS AND VIEW OPITONS
Binding Proteins Matter
Tuesday, May 12, 2015 1:36 pm Email this article
Many overweight patients take vitamin D or testosterone supplements prescribed by their primary care doctor. Few patients need it. Here is what is going on.
Vitamin D and testosterone molecules in the blood exist in two states: (A) bound, i.e. stuck to a binding protein, or (B) floating free. Only the molecules floating free bind to a receptor and have an effect. In the case of testosterone just 1% floats free. All the rest is bound & inactive.
When your doctor orders a simple vitamin D or testosterone level, the laboratory returns a single number which is the total of both the free fraction and the bound fraction. But as you see, it is only the free fraction that matters.
When people gain weight, the amount of the binding protein in the blood goes down. So the total amount of vitamin D or testosterone in the blood goes down, but the free fraction remains the same.
Doctors should measure the free fraction only. Then this silly belief that almost all people are deficient in vitamin D and men are deficient in testosterone would fade away.
Do not take a vitamin D or testosterone supplement "just in case". Either do the right blood test or don’t take the supplements as all, because too much vitamin D or too much testosterone causes problems.
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