Thyroid-Stimulating Hormone: Why Test It & What High and Low TSH Levels Mean

By Michelle Darian, MS, MPH, RD, July 6, 2023

Mature couple sitting on a couch talking to a doctor

Thyroid-stimulating hormone, commonly referred to as TSH, is the most sensitive marker of thyroid function. It’s released from the pituitary gland in the brain but acts on the thyroid gland, therefore, controlling the activity of the thyroid hormones that regulate metabolism, body temperature, bone growth, nervous system development, and blood pressure regulation. So high or low TSH levels can have notable symptoms and clinical implications that require the care of a physician. Thyroid concerns are more prevalent in women than men, however, everyone should have their TSH levels evaluated—as it is the most sensitive blood biomarker of thyroid function. 

TSH levels are measured through a blood test, which can be ordered by a physician or through services like InsideTracker. InsideTracker measures TSH and provides insights into how your TSH levels may be impacting other blood biomarkers and offers guidance on how to help optimize your levels that fall within the standard reference range.

Here, we break down TSH blood testing, what lab results mean, and how levels may influence other markers of health. 

Womens Health-01-min

What is thyroid-stimulating hormone

TSH is a blood biomarker that assesses thyroid function. The thyroid is a butterfly-shaped endocrine gland in our neck that regulates hormone production and usage throughout the body. 

The pituitary gland, the “master regulator” of the endocrine system in the brain, produces TSH. Circulating thyroid hormone levels, triiodothyronine (T3) and thyroxine (T4), influence the amount of TSH produced by the pituitary gland. [1]


What role does TSH play in the body? 

Thyroid hormones are best known for their role in metabolic regulation and act on almost every cell in the body. Metabolism refers to processes in the body that consume and use energy for the growth, repair, and maintenance of cells, tissues, and organs in the body. Thyroid hormones stimulate metabolic functions like lipogenesis and lipolysis, the creation and breakdown of fats for energy, and energy storage and expenditure. [2]

The metabolic impact of these hormones also influences other bodily processes like temperature regulation, bone growth, nervous system development, and blood pressure regulation, all of which contribute to one’s overall health. [2]

The negative feedback loop of thyroid-stimulating hormone

What is the reference range for a TSH test? 

Blood test results are often displayed against a reference range. Levels that fall outside of the reference range—say they’re too high or too low—should be addressed with your healthcare practitioner, as they may indicate a medical concern. 

The reference range for TSH differs between males and females and depends on multiple factors like age, sex, and menopausal status. [3]


Normal reference range for TSH

18-50 years 0.5-4.15 ng/mL
50 + years 0.5-4.59 ng/mL
Women Premenopausal 0.4-4.1 ng/mL
Perimenopausal 0.4-4.7 ng/mL
Postmenopausal 0.4-4.7 ng/mL


What do low TSH levels mean? 

Low TSH levels most often indicate thyroid overactivity, also known as hyperthyroidism. It may sound counterintuitive, but the overactivity of the thyroid likely means that the body is producing excess thyroid hormones. An overactive thyroid produces excess amounts of triiodothyronine (T3) and thyroxine (T4)—the main thyroid hormones. High T3 and T4 levels signal the pituitary gland (a part of the brain) to produce less TSH, resulting in lower blood levels of TSH. It's encouraged to discuss low TSH levels with your physician. [1]

The presence of decreased TSH levels is associated with several symptoms. It’s important to note that these symptoms can also be commonly experienced by those who do not have improper thyroid function. 

  • Unintentional weight loss [4]
  • Irregular heart beat [4]
  • Muscle weakness [5]

*TSH levels are important to monitor and optimize because low TSH levels are linked to notable symptoms and may have clinical implications. It’s encouraged to discuss low TSH levels with your physician. 


What do high TSH levels mean? 

Elevated TSH levels most often indicate reduced thyroid function, also known as hypothyroidism. High TSH levels indicate that the body is not optimally responding to the initial signal to produce thyroid hormones. 

Due to the role of TSH in regulating many metabolic processes, high TSH levels are associated with an increased risk of certain metabolic conditions. And these conditions appear to be pronounced in postmenopausal women. 

  • Menopausal symptoms: Hypothyroidism, indicated by high TSH levels, can increase or worsen symptoms of menopause. [6
  • Metabolic syndrome: A study of 2,205 postmenopausal women found that participants with higher TSH levels were at an increased risk of metabolic syndrome compared to those with normal TSH levels. [7]
  • Type II diabetes: In fact, a meta-analysis of over 337,000 participants found that high baseline TSH levels were related to a 17% higher risk of type II diabetes, compared to those with normal TSH levels. [8]
  • Measures of heart disease risk: Risk of atherosclerosis and myocardial infarction is increased in older women who have elevated TSH levels, compared to those with normal TSH levels. [9]

The presence of elevated TSH levels is associated with several symptoms. It’s important to note that these symptoms can also be commonly experienced by those who do not have improper thyroid function. 

Symptoms include: [10, 11]

  • Fatigue 
  • Poor mood
  • Weight gain 
  • Joint pain 
  • Irregular menstrual periods
  • Constipation

And postmenopausal women may be more susceptible to higher TSH levels than men. Postmenopause—which begins one year after a person’s last menstrual cycle—is characterized by consistently low levels of the hormone estrogen. Estrogen has multiple protective effects on health, and there’s now research to suggest that low estradiol levels may impair the thyroid's ability to produce hormones, resulting in higher blood levels of TSH. [4]

*TSH levels are important to monitor and optimize because high TSH levels are linked to notable symptoms and may have clinical implications. It's encouraged to discuss elevated TSH levels with your physician and to measure other markers of hypothyroidism, like Free T4, Free T3, Reverse T3, and thyroid antibodies.


How do TSH levels affect other blood biomarker levels? 

TSH and other thyroid hormones are intricately connected to many other processes in the body. So, it’s no surprise that scientific literature points to significant connections between TSH biomarker levels and additional metabolic and hormone blood biomarker levels. The chart below describes how biomarkers are correlated to TSH and the mechanism behind it, given the current scientific literature.  


Impact of TSH on other blood biomarkers 
Elevated TSH

Increased triglycerides

Increased total cholesterol 

Increased LDL cholesterol 

Elevated TSH levels indicate metabolic abnormalities. And because TSH is involved in the breakdown and removal of cholesterol markers, elevated levels of TSH (underactive thyroid function) impair the body’s ability to clear excess cholesterol levels, resulting in elevated blood levels of total cholesterol, LDL cholesterol, and triglycerides. [6, 12, 13]
Decreased calcium  Elevated TSH levels are associated with decreased calcium and phosphorus levels—and vice versa. [14]
Increased creatine kinase [15] Hypothyroidism affects skeletal muscle, which can increase serum creatine kinase levels. [15]
Increased cortisol [11] Increases in metabolic stress associated with elevated TSH can also increase cortisol production. [11]
Decreased ferritin [16] One study suggests that high TSH levels can disrupt iron-dependent enzymes, but more research is needed to understand this relationship. [16]
Low TSH Increased testosterone

Decreased TSH levels, or an overactive thyroid, can impact other hormone levels like SHBG and testosterone. [17]

Increased sex hormone binding globulin (SHBG) 
Decreased free testosterone (women) 


Can you improve unoptimized TSH levels?

TSH levels that fall outside of the reference range may be due to an underlying condition that should be addressed with a healthcare practitioner, who may recommend medication to correct the imbalance. 

An InsideTracker analysis displays TSH blood test results using the reference ranges provided but takes it a step further by creating optimal zones based on sex and menopausal status (pre, peri-, or postmenopausal) for females and age for males. For lab values that fall outside of a given optimal zone, a person may see recommendations for food, supplements, and/or physical activity recommendations that can positively impact TSH levels.


How can you get your TSH levels measured? 

A TSH blood test is generally included in a standard thyroid hormone panel, but this panel is not always included in bloodwork for a yearly physical unless there’s a family history. 

And continually reassessing thyroid hormones is the most important next step in thyroid health management. One study of 107 people with above-optimized TSH (considered subclinical hypothyroidism), revealed that 52% of individuals achieved normal levels again within the next two and a half years, while only 5.6% of them actually developed clinical hypothyroidism. [18].  In addition, researchers followed a large group of 1,507 people with a baseline TSH level of  0.1–0.4 mIU/mL over time and found that the progression to overt hyperthyroidism was just 0.5%, 0.7%, and 0% two, five, and seven years later, respectively. [19]. 

Knowing your TSH levels can provide critical insight into your thyroid health—and can help to determine your next course of action, whether that’s no change to your current routine, or speaking with your physician about your results.  

When you measure your TSH with InsideTracker’s Ultimate Plan, you can track your levels over time, understand its impact on your other biomarkers, and receive recommendations aimed at improving this marker. As the thyroid plays an essential role in so many body systems, InsideTracker recommends monitoring your TSH levels and sharing the trends with your healthcare provider for clinical support.






















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