Friday, September 21, 2012

Too Much of a Good Thing: Levothyroxine vs Dementia

You can never be too rich or too thin. -- Wallis Simpson

The above quote also makes me think of the philosophy that if a little bit is good, then a whole lot more must be better yet.  Obviously, all these authors & speakers have never heard of Goldilocks, who wanted things just right, rather than at the extremes.  Of course, this begs the question as to what is a normal reference range.  And does the normal range vary according to age & gender?

I bring up this point since we use TSH or thyroid stimulating hormone as the de facto judge to monitor thyroid status.  Yet, in a prospective study published early online last week prior to its print publication in the Journal of Clinical Endocrinology & Metabolism, the authors concluded that high free (levo)thyroxine (FT4) levels are associated with dementia.  It's especially important to note that FT4 remained within normal limits and that TSH made no impact on dementia risk.

While the data is only associative and not gold standard randomized controlled trial demonstrating proof of causation & effect between placebo vs medication, it does make one give pause when asked towards what TSH level we should aim when treating patients w/hypothyroidism.  In the past, I might have suggested taking as much levothyroxine as could be tolerated without suffering any potential side effects.  Now, I'm no longer so sure.  What will you do with the results of this new study?

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