The troubles with Thyroid Stimulating Hormone (TSH) keep coming. I continue writing about it because relying on TSH alone to fully assess thyroid function, (as the vast majority of doctors do) is a horrible disservice to the patient (you in other words). Since doctors appear to be poorly educated in this regard, it becomes your responsibility to educate yourself and your physician. So we slog on!

In the prior three TSH blogs (please read them before this one), you learned what TSH is and does, and the many reasons why relying on TSH alone to completely assess thyroid function is plain madness. Current lab ranges are inaccurate. TSH is suppressed by certain drugs. Thyroid replacement therapy lowers TSH. TRH, a hypothalamic hormone, is lowered when TSH is lowered and this is turn reduces vagus nerve output, affecting the entire digestive function and increasing inflammation. In a vicious cycle, low TSH decreases absorption of iodine by tissues, which can aggravate an iodine deficiency, which further reduces the thyroid’s ability to produce thyroid hormones, which increases the need for additional thyroid hormone replacement, which decreases TSH even more. If you have osteoporosis, low TSH is a no-no. A part of the TSH molecule has a positive effect on osteoblasts, the cells that build bone, so diminished TSH can potentially make osteoporosis worse.

Now for the new information on the importance of maintaining an optimal TSH level. It appears that TSH levels at the high or low end of currently accepted “normal” ranges have significant adverse effects on multiple aspects of health. Mildly decreased thyroid hormone levels, within the currently accepted “normal” range can lead to elevated LDL cholesterol levels. In addition, elevated TSH levels alone, even if thyroid levels aren’t low, can raise cholesterol. Studies reported that patients with TSH in the upper normal range were more likely to have higher cholesterol. 

In a just-published 2023 study, 119,000 people from the general population were followed for an average of seven years to test the hypothesis that low TSH levels were positively associated with increased cardiovascular disease (CVD). They observed that TSH below the median level expressed a positive relationship to CVD. The median level was 1.53mlU/L. People in the lowest 5% (0.54mlU/L) were 12-27% more likely to suffer from conditions including atrial fibrillation, heart attack, stroke, aortic valve stenosis, and heart failure. 

To complicate matters, a 2013 clinical review of other research articles determined that higher TSH, along with lower thyroid levels, both within the accepted normal ranges, are associated with more cardiovascular risk factors, worse metabolic factors, and poorer pregnancy outcome. Just the opposite, lower TSH/higher thyroid hormone levels was associated with reduced bone mineral density and increased risk of fracture.

It appears that both low and high TSH within the currently accepted normal range can have negative consequences. The question becomes, “what is the normal (i.e. optimal) range”. At this time there is no agreement, but one thing is apparent. What was once considered normal no longer is. When the TSH test first came out around 1971, the upper limit was set at 15mlU/L, then 10mlU/L, and now around 4.5mlU/L, depending on the lab. Low TSH wasn’t considered important. Presently, LabCorp’s normal range is 0.45-4.5mlU/L. From the information presented in my four TSH blogs, a range between 0.7-3.0mlU/L would seem to be optimal.

Now you may ask, “What do I do if my TSH is outside the optimal range”. First, there would be no point in going to your standard allopathic physician who has limited (I’m being kind) knowledge of this area. Second, read the rest of my blogs on this website the explain the intricacies of assessing and treating thyroid issues, then seek council from a Functional Nutrition  physician trained in the treating functional thyroid issues. 

About the Author: Dr. Douglas L. Weed

Dr. Weed practices Functional Nutrition, Chiropractic care, and offers weight loss solutions in Napa, CA at Heun Chiropractic, Inc. He has a doctorate in Chiropractic care and he has received certifications in physical rehabilitation and as a Qualified Medical Examiner. With a post-graduate certification in Functional Medicine, focusing on functional endocrinology, digestive disorders and Peripheral Neuropathy, he is committed to lifelong education and helping patience transform their health.