Brain Barrier?

[Guest guest]

Has anyone read this article? Has anyone else heard that T3 cannot cross the barrier into the brain and that the brain converts its own T4 and that's the only way it can get T3???http://www.thyroid-info.com/articles/dommisse.htm"Secondly, treating with T3-only is almost

as bad as treating with T4-only in most

cases and worse than T4-only in some

cases. I say 'almost as bad' because,

since 90% of thyroid function is carried

out by T3, correcting the T3 level is a

good thing. However, the brain needs T4

to be present in the blood in a good

amount because T3 doesn't cross the

'blood-brain barrier' and get into the

brain directly. T4 has to get into the

brain first and then convert to T3 in the

brain tissues. So the cognitive effects

of a low T4 level would continue because

T3-only treatment raises the T3 level a

lot, often way above normal (with all the

dangers inherent in that situation), and,

by lowering the TSH level, this also

lowers the T4 level to way-below normal. I cannot understand why anyone

would want to treat with T3-only and not use both thyroid hormones, as

needed to optimize BOTH free-levels. This is not to deny that many people

treated with T3-only will improve in many ways; after all, T3 is a very

important hormone; but they would improve much better and with less

ill-effects if both their FT4 and FT3 levels are optimized and neither one

is overtreated or undertreated."