Too Much Thyroid is Not a Good Thing for Your Brain

July 25, 2016

Too Much Thyroid is Not a Good Thing for Your Brain



 What is too much thyroid? Our bodies have a unique method of telling us if we think we are getting enough thyroid hormone. Thyroid hormone is made in our thyroid gland, in the front of our necks. T4 is the substrate molecule that circulates in your body for 36 hours and is gradually changed to T3 by the enzyme de-iodinase. Your hypothalamus in your brain reads how much T4 and T3 it is receiving and decides if that is enough for it to be happy. It then communicates with your pituitary gland to make TSH (Thyroid Stimulating Hormone) to nudge the thyroid to make more. TSH has become the established norm for deciding about sufficient thyroid. 

This study looked at TSH levels and the subsequent development of dementia. Keeping a healthy brain is one of our highest priorities. As we get older, dementia robs us of our relationships, our memories, and just about everything that is meaningful and important. What this study found was that a LOWER TSH (meaning that your brain thinks you can back off a little on thyroid production) is associated with greater increase of dementia. 313 non demented Koreans were evaluated and followed for 5 years with thyroid testing and mental status testing. Now, the average TSH in the healthy brain group was 2.24 and in the group that showed MCI (mild cognitive impairment) it was 1.78. Those are both, technically, normal. 

Stated differently, for every 1 mIU/L decrease in TSH, there was a 1.7 fold increased risk for MCI progression. If you already had MCI, a 1 mIU/L decrease in TSH resulted in a 6.8 times risk of progression to frank dementia. Ouch! This isn't completely new. The Rotterdam Study in 2000 showed that a TSH below 0.4 (frankly too low - meaning way too much thyroid hormone) had a 3 fold increased risk of developing dementia. That study followed 1843 non demented people for just 2 years. The Framingham study published in 2008 followed 1864 folks and showed that a TSH between 0-1 had a doubling of Alzheimer's risk. 

There are more, and all say the same thing. Lower TSH means higher risk for dementia. Traditional Internal Medicine focuses purely on the TSH. Functional medicine asks us to look at the free T3, reverse T3 and TSH combined. You get a richer picture when you look at all three, but I find there are frequent conflicts where the free T3 is "technically low", but the TSH is still normal.  Insufficient thyroid or low thyroid (shown by HIGH TSH) isn't good for your brain either. But that's for another day. 

 Bredesen, my guru for Alzheimer's prevention, asks for TSH between 1-2. He doesn't reference free T3. The big question then comes, which reference point is the most important. 

 WWW.What Will Work for Me. I'm very interested in this. We aren't as clear as we would like to be on this topic. For now, I'm putting my chips on Bredesen. For myself, I take a bit thyroid hormone to keep my own TSH between 1-2. Should I let it drift up to 2.4? Stay tuned. 

 Pop Quiz

1. A high TSH means your are getting too much thyroid? T or F?                         Answer:  False. This is the mistake of a first time reader. TSH is STIMULATING hormone. A high TSH says your brain thinks you aren't getting enough, and is trying to get your tired old thyroid to make more. 

 2. This article is the first to show that lower TSH's, in the normal range predict cognitive decline in Koreans. T or F?                         Answer:  Exactly the point. What's new is that these folks were in the normal range and they were followed for longer than prior studies. 

 ‪3. Korean's brains are different than ours, so I don't need to worry about it. T or F?                  Answer:  Sorry, despite the behavior of certain N. Korean leaders who might bring this into question, all of our brains are the same. It's nice to see the robust Korean medical community starting to contribute to the world body of knowledge. 

 4. There is a clear connection between free T3 and TSH? T or F?                       Answer:  As things currently stand, it's partially right but mostly helpful when your thyroid function is low, resulting in a higher TSH, now lower. 

 5. Some of our best Alzheimer's treatment leaders use thyroid as part of their decision making for Alzheimer's treatment. Goal: TSH 2-4.5 T or F?                                Answer:  Trick question. True, they use it. False. Modern internal medicine says up to 4.5 TSH is ok. Bredesen aims for a TSH between 1-2. Details matter. Low thyroid isn't any good either.