Normal Healthy Thyroid Levels Vs. Dangerous Levels

Updated April 17, 2017

There is much confusion as to what a normal thyroid level is. Since there is more than one type of thyroid disease, thyroid levels that are considered dangerous differ between each type. Hence, there are tests performed that determine what an individual's thyroid level is, and proper treatment can be given before such dangerous levels cause serious health issues.

The Facts

There are two types of thyroid disease: hyperthyroidism and hypothyroidism. Hyperthyroidism occurs when the thyroid is overactive, and hypothyroidism occurs when the thyroid gland is underactive. Testing of thyroid stimulating hormones (TSH) determines whether one falls under either of these conditions, or if their thyroid activity is within normal range. Such tests are also conducted on newborns.


The pituitary gland produces TSH. The thyroid gland then responds by creating hormones called triiodothyronine (T3) and thyroxine (T4). These hormones affect numerous body functions, such as metabolism, blood flow to the heart, blood pressure, and weight. A low TSH result indicates that the thyroid gland is overactive, and is producing too many hormones. A high TSH result is indicative of hypothyroidism, because the thyroid is not responding properly to the pituitary gland, and thus, is not creating enough hormones.


Normal TSH levels are considered to be anywhere between 0.4 to 4.0 mIU/L. These levels indicate that there is no thyroid dysfunction present. Individuals who are undergoing treatment for either hypothyroidism or hyperthyroidism should have TSH levels of 0.5 to 3.0 mIU/L. Any levels lower indicate that the thyroid is overactive. Higher levels indicate that the thyroid is underactive, and that hormone replacement medication is needed. If medication is already being used, then the dosage will be increased.


Initial blood tests are conducted to read TSH levels, and sometimes T3 and T4 levels as well. Once an individual is diagnosed with hypo- or hyperthyroidism, then regular blood tests are given to ensure that the proper amount of treatment is being given. For example, a hypothyroid individual taking Levothyroxine will be given monthly tests and the dosage will be adjusted accordingly until TSH levels come back normal.


TSH levels can reach a dangerous level when a thyroid disorder is not treated properly, or goes undetected for a significant amount of time. A study of 3,000 people was done by epidemiologists for the Journal of the American College of Cardiology for 12 years to uncover possible dangers associated with high levels of TSH. The study revealed that individuals who had a TSH level of 10 mIU/L or higher were at twice the risk of heart failure than individuals who had low TSH levels. Thus, the study reveals that there is a direct link between TSH levels and heart health.

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