Subclinical Hypothyroid: Underdiagnosed Thyroid Condition

Tired? Bloated? Dry skin and hair? Constipated? Many people write off these symptoms as part of growing older. But these common conditions may not be due to aging. Those who suffer from them could have a condition that even their physician may fail to identify: subclinical hypothyroidism.

Learn more about thyroid health below, or listen to the podcast on in which Life Extension’s own Michael A. Smith, MD, discusses the latest information.

What is subclinical hypothyroidism?

The difference between hypothyroidism and subclinical hypothyroidism

Many of us know about hypothyroidism (low thyroid hormone levels), but what is subclinical hypothyroidism? Subclinical hypothyroidism has been defined by American Thyroid Association (ATA)/American Academy of Clinical Endocrinology (AACE) guidelines as the presence of a serum thyroid stimulating hormone (TSH) above the upper reference limit in combination with normal free thyroxine (T4). They note that “This designation is only applicable when thyroid function has been stable for weeks or more, the hypothalamic-pituitary-thyroid axis is normal, and there is no recent or ongoing severe illness.”1

“Sub,” when used as a prefix, means “under” or “below,” and “subclinical” refers to a health condition that may not be overtly apparent and can be underdiagnosed according to standard assessments like bloodwork. Individuals with subclinical hypothyroidism are often asymptomatic, however they may experience the non-specific complaints associated with overt hypothyroidism. Symptoms could include fatigue, weakness, weight gain, cold intolerance and constipation. The condition often precedes the development of overt hypothyroidism.2

If thyroid problems are suspected, clinicians will often test only TSH levels. If TSH levels are outside the normal reference range, T4 levels may then be tested as well. Individuals with high TSH levels and normal T4 levels may have subclinical hypothyroidism.

Thyroid stimulating hormone normally rises in response to a decline in thyroid hormones—increasing thyroid hormone levels should therefore decrease TSH levels. According to the American Thyroid Association, a “normal” TSH range is between 0.4-0.5 mU/L on the lower end and 4-5.5 mU/L on the upper end.3

What are subclinical hypothyroidism treatment guidelines?

The European Thyroid Association (ETA) Guideline for the management of subclinical hypothyroidism recommends the drug levothyroxine (L-thyroxine), the synthetic form of T4, for patients younger than 60 to 70 years with TSH levels of greater than 10 mU/L, even in the absence of symptoms. For patients in this age group with TSH levels of less than 10 mU/L who have symptoms of hypothyroidism, they suggest a trial of levothyroxine, followed by a review of one’s response three to four months after a normal TSH level is attained. Among those who are older than 80-85 with elevated serum TSH levels of 10 mU/L or less, the ETA recommends generally avoiding hormonal therapy, but if the decision is to treat the patient, they recommend daily levothyroxine supplementation with a TSH recheck after two months.4

The hormone T4 normally converts to T3, another essential thyroid hormone. In theory, supplementing with T4 should be all that is needed. However, it is possible that not everyone efficiently converts T4 to T3. Individuals using levothyroxine who continue to experience symptoms of hypothyroidism when TSH levels have normalized may wish to have their T3 evaluated. In addition to TSH and T4, a complete thyroid panel will also measure free T4, free tri-iodothyronine (T3), reverse T3, thyroglobulin antibody (ATA) and thyroid peroxidase antibody (TPO).

If one has low T3 levels, the drug Cytomel, which is synthetic T3, may be prescribed in addition to levothyroxine (T4). It is not yet clear whether combination therapy is more effective than levothyroxine monotherapy, however those who do not respond well to monotherapy may consider combination treatment under the guidance of an experienced clinician.5 An alternative is treatment with Armor Thyroid, NP Thyroid or Naturethroid, which contain desiccated bovine thyroid gland tissue that naturally contains T3 as well as T4.

Is subclinical hypothyroidism dangerous?

Low-normal thyroid function may increase total and low-density lipoprotein (LDL) cholesterol and triglycerides and may be associated with metabolic syndrome, insulin resistance and chronic kidney disease.6

Can subclinical hypothyroidism be reversed?

Nutrients that support thyroid function

With the correct dosage of thyroid hormone replacement and periodic blood testing to evaluate the efficacy of the dosage one has been prescribed, subclinical hypothyroidism can be normalized.

There are also several nutrients that support thyroid function. Iodine is the first that comes to mind, due to its necessity for the synthesis of the body’s thyroid hormones. Other minerals that are supportive of thyroid function are selenium and zinc, which are important for the conversion of T4 to T3.7,8 Preclinical studies suggest that the herb Commiphora mukul (guggul) may also be helpful for this purpose.9

Another herb that may help support the thyroid is ginseng. A study of patients with congestive heart failure found an increase in T3 and T4 levels (which, prior to treatment, were lower than those of normal control patients) among participants who received ginseng for two weeks.10

A small study involving supplementation with the ayurvedic herb ashwagandha (Withania somnifera) resulted in increases in T4 after 8 weeks among all those who received the herb and even normalized subclinical hypothyroidism in one patient, while most of those who received a placebo experienced a decline in T4. These initially promising findings suggest a potential use for ashwagandha in subclinical hypothyroidism.11

The Bottom Line

A study involving a sample of 13,344 participants in the National Health and Nutrition Examination Survey III (NHANES III) who were representive of the geographic and ethnic distribution of the U.S. population revealed subclinical hypothyroidism among 4.3% of the subjects.12 Other estimates of the prevalence of subclinical hypothyroidism are higher, and older women are particularly at risk.13

If you are suffering from some of the symptoms of hypothyroidism, it would be well worth your while to rule out this frequently undetected condition, not only to feel better, but to help protect your future health.

About Live Foreverish: Join Dr. Mike as he sits down with some of today’s leading medical, health and wellness experts to discuss a variety of health-related topics. From whole-body health to anti-aging and disease prevention, you’ll get the latest information and advice to help you live your life to the fullest. If you like what you hear, please take a moment to give Live Foreverish a 5-star rating on iTunes!


  1. Garber JR et al. Endocr Pract. 2012 Nov-Dec;18(6):988-1028.
  2. Baumgartner C et al. Swiss Med Wkly. 2014 Dec 23;144:w14058.
  3. Woodmansee WW. Clinical Thyroidology for the Public. 2018 Feb;11(2):3-4
  4. Pearce SHS et al. Eur Thyroid J. 2013 Dec; 2(4): 215–228.
  5. Dayan C and Panicker V. Thyroid Res. 2018 Jan 17;11:1.
  6. van Tienhoven-Wind LJ et al. Eur J Clin Invest. 2015 May;45(5):494-503.
  7. Kawai M. Pediatr Endocrinol Rev. 2019 Mar;16(3):307-310.
  8. Nishiyama S et al. J Am Coll Nutr. 1994 Feb;13(1):62-7.
  9. Panda S et al. Phytother Res. 2005 Jan;19(1):78-80.
  10. Dai X et al. Zhongguo Zhong Xi Yi Jie He Za Zhi. 1999 Apr;19(4):209-11.
  11. Gannon JM et al. J Ayurveda Integr Med. 2014 Oct-Dec;5(4):241-5.
  12. Hollowell JG et al. J Clin Endocrinol Metab. 87:489–499.
  13. Wilson GR et al. Am Fam Physician. 2005 Oct 15;72(8):1517-24.


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