> > I have always wondered if you drink so much water does it affect your
> >kidneys adversely by overworking them ?
> >
>
>
> James here.....
>
> It would be interesting to see what Dr John has to say, it is so nice to
> have him on the list. I have always understood by making urine more dilute
> it is better for you.
Normal kidneys filter a straight percentage of the amount of blood that
passes through it. This is an oversimplification of a process that involves
the amount of dissolved salts, serum proteins and blood pressure, but for
purposes of this list, suffice it to say that a fixed fraction of the amount
of blood that passes through the kidney is excreted as urine. Thus, the
more blood volume that passes through, the more urine made. The blood
volume is increased by consumption of more fluid, but the intestines can
absorb fluid at a fixed rate in the hydrated state (again, an
oversimplification). If one consumes more fluid than one can absorb, the
stool is more hydrated; if there is enough fiber, it absorbs it; if not, the
stool becomes loose. OTOH, intravenous fluid has no limit in how much can
be put into circulation.
The reason there are limits to absorption is not because of the kidneys but
because the heart has a limit to how much it can pump through the kidneys.
If the limit of cardiac output is reached, fluid accumulates in higher
volumes in the blood and the fluid pressure forces it into the tissues,
resulting in edema. Again, orally, this is almost impossible to do in a
healthy person.
If fluid intake is maximized, urine is very dilute when it is made since
much more water is put into the urine. If fluid intake is maximized, the
blood flow to the mucus membranes is adequate so the mucus glands can
produce mucus that is thinner. As the volume of blood drops, the
circulation is reduced to noncritical organs such as the airways in favor of
the brain and other critical organs. Consequently the mucus gets more
viscous.
Other benefits to adequate hydration are reduced incidence of bladder
infections for women by reducing the chance of bacterial growth to the point
of invasion of the bladder wall, improved perspiration for temperature
regulation, improved skin hydration, reduced risks for stone formation in
the kidneys and salivary glands, etc.
I hope that explains it.
John
John J. Messmer, M.D.
Assistant Professor, Family & Community Medicine
Penn State College of Medicine
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