Thyroid Hormone Testing: What’s the Best TSH Level?

Friday Jul 25 | BY |
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Thyroid Testing

Your doctor says you don’t need treatment, but could he or she be wrong?

Thyroid-stimulating hormone (TSH) is secreted by cells in the front part of the pituitary gland. This tiny area in the brain regulates the key endocrine function of the thyroid gland by stimulating production of thyroxin, the main thyroid hormone.

TSH is the main hormone tested by your doctor to determine if your thyroid gland is functioning properly. Too much TSH means the pituitary gland is trying to get a sluggish thyroid gland to work better. Too little means there is enough thyroxin in your body so TSH remains low until more is needed.

If the TSH is too high you have a condition called hypothyroidism, or an under-functioning thyroid gland. If it’s extremely low, you have an overactive thyroid gland, or hyperthyroidism.

Recommended TSH Levels May Not Be Right

Clinical chemists and doctors decided decades ago that healthy people with normal functioning thyroid glands have TSH levels within a range of 0.450 to 4.500 mIU/L (and some labs go as high as 5.000mIU/L). In clinical shorthand, the diagnostic range is rounded out to 0.4-4.0.

When diagnosing underactive thyroid function, most conventional physicians consider TSH levels above 10 mIU/L as thyroid failure, and levels between 5–10 mIU/L as mild hypothyroidism. This means that if your TSH is 4.0-4.5, your conventional doctor won’t diagnose hypothyroidism and therefore, won’t treat you.

In recent years, however, clinical scientists and practicing physicians have found that the standard range is too broad. Many people have symptoms of low thyroid function even when their TSH is well below the upper level of the standard reference range.

Chart 1

The TSH Controversy

A debate ensued between conventional MDs, physician members of the American Association of Clinical Endocrinologists, and the National Academy of Clinical Biochemistry. It wasn’t too long afterwards that integrative medical doctors added their opinion. Each group suggested a slightly different range from the others, but all agreed that the upper limit was set too high.

Naturopathic doctors (ND) have their own view. NDs practice personalized medicine taking into account individual variations, genetic tendencies, as well as age and gender differences. The naturopathic profession developed integrative therapies, but MDs took the credit. Early on in the TSH controversy, NDs read the scientific literature and found that at least 60 percent of patients taking Synthroid do not have TSH levels in the normal range. They also found that many patients with TSH levels above 2.0 have symptoms associated with an underactive thyroid gland.

Symptoms of Low Thyroid Function:

  • Unexplained fatigue
  • Dry, rough and scaly skin
  • Pale and cold skin
  • Hair falling out, and coarse brittle hair
  • Sensitivity to cold
  • Decreased sweating even during exercise
  • Constipation
  • Difficulty losing weight
  • Depression
  • Muscle weakness
  • Unexplained muscle and joint pain

A study in 2000 published in the Annals of Internal Medicine found that older women with subclinical hypothyroidism were twice as likely to have blockages in their arteries than women with normal TSH levels.

In 2008, a study in JAMA found that those with subclinical hyperthyroidism were more like to have irregular heart rhythm. These findings suggested to doctors that tighter TSH ranges were advisable.

Along with more accurate TSH testing, narrower ranges were recommended, and integrative medicine doctors were in agreement.

Optimal TSH

What’s the best TSH level for your body? There is no magic TSH level that fits all. There are individual variations, and some general guidelines. When you get tested, make sure that you’re TSH level is within the standard laboratory ranges.

Chart 2

If your level is too high, or too low, discuss treatment options with your doctor. If your TSH level falls between 3.5-4.5, but you have many of the symptoms of hypothyroidism, find an integrative medicine practitioner who will help you achieve a level within the desirable range.

Remember, individual variations matter. For some people their optimal TSH may have to be in a very tight range of 1.0-1.5.

Successful treatment for hypothyroidism may involve thyroid hormone replacement therapy, but also requires supportive nutritional supplementation including trace minerals like iodine and selenium. Other treatments including acupuncture may be necessary to help restore normal thyroid gland function.

Thyroid disease is common. The thyroid gland seems to get tired with age, exposure to infection, stress, and toxic chemicals in the air, as well as in the water supply and food chain. Remember, hypothyroidism is a very treatable condition. There is no reason to go untreated, or to get inadequate treatment.

Have you suffered with thyroid problems? What did your doctor advise? Please share your story.

Dr. J. E. Williams


Dr. Williams is a pioneer in integrative and functional medicine, the author of six books, and a practicing clinician with over 100,000 patient visits. His areas of interest include longevity and viral immunity. Formerly from San Diego, he now resides in Sarasota, Florida and practices at the Florida Integrative Medical Center. He teaches at NOVA Southeastern University and Emperor’s College of Oriental Medicine.

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  1. June Hanson says:

    Oh, my Doctor, is the best. Keeps my thyroid perfect and healthy. Along with the rest of my body. Looking forward to a healthy and bright future, as I have so much confidence in him!! That is, if he doesn’t get too comfortable in that deep Amazon Rainforest or those high Peruvian Andes!!!


  2. Lilija says:

    Few months ago I had 500,58 uIU/mL for TSH. Crazy, right?
    Then I got diagnosed with Hashimoto’s. Weirdest thing was that I had barely any symptoms (which I connected only after the diagnosis). I tested it just for the sake of check-up, I had no suspicion at all.

  3. Casey says:

    I have personally experienced the frustration of being told there is nothing wrong with my thyroid when there clearly was – my best advice to anyone is if you think you have a thyroid issue, demand that your Dr. test you more than once at different times of the day and month. I have been going in with clear symptoms of hypothyroidism since 2008 and my TSH levels were tested over that period more than 10 times, always falling just slighly under 4.500 mIU/L (anywhere from 4 to 4.5). I was told repeatedly that all my tests were fine, and they refused to let me see a thyroid specialist.

    I decided to start the whole process over again with an Integrative medicine Dr. now that I have worked aggressively to clean up my diet, and was still experiencing symptoms. My TSH level was 5.4 mIU/L this time, and I’m finally getting the referral I’ve been beggging for, for years. In can be an incredibly frustrating process until conventional medicine gets with it – don’t give up!

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