TSH (Thyroid stimulating hormone) – and what your results really mean for optimal health, metabolism and longevity
TSH is produced and secreted by the pituitary gland and stimulates the thyroid to make T3 and T4. Increased TSH levels may indicate low thyroid function. When TSH is low, it may indicate high thyroid function. TSH is used as a first-line screening tool to assess thyroid disease; however, by itself it is insufficient, and needs to be evaluated in conjunction with other thyroid markers such as T3, T4, thyroid antibodies, and other tests.
Important to note is also that TSH may be mildly suppressed in acute illness and mildly elevated during recovery from acute illness.
However, TSH values are typically not suppressed to < 0.1 mIU/mL or elevated to > 10 mIU/mL in these circumstances. Thus, a patient seen by their primary care provider with a minimally abnormal TSH in, or recently discharged from, the hospital should simply have the thyroid function tests repeated in several weeks (R).
Circadian Variability
It is important to note that TSH secretion follows a circadian rhythm, with maximal levels seen in the early morning and a nadir in the late afternoon to mid-evening. While generally not resulting in TSH values outside the normal range, this circadian rhythm may cause a variation in TSH by a mean of between 0.95 mIU/mL to 2.0 mIU/mL, which could affect treatment decisions. Also, this circadian rhythm appears to remain intact in patients with subclinical hypothyroidism, and in one small study 50% of patients with a mildly elevated TSH between 8:00–9:00 am had a normal TSH (< 4.0 mIU/mL) when assessed between 2:00–4:00 pm (R).
What thyroid hormones are needed for
A properly functioning thyroid is important for many functions in the body, including:
- Metabolism
- Energy
- Heart rate
- Healthy cholesterol levels
- Mental and brain health
- Bone health
- Fertility
And many other functions. (R).
Common symptoms associated with suboptimal TSH levels
An overactive thyroid may cause:
- Excessive sweating
- Diarrhea
- Headaches
- Chest pain.
A low thyroid function can contribute to a broad array of symptoms, as thyroid hormones affect essentially every cell of our body- particularly in determining our metabolism. Some of the most common symptoms include:
- Tired or sluggish despite adequate sleep
- Weight gain or weight loss resistance
- Low mood, depression, slowed thinking or brain fog
- Cold intolerance
- Constipation, low production of stomach acid, pancreatic enzymes and intestinal motility, increased risk of SIBO and other digestive problems
- Hair loss, weak or brittle nails
- Dry skin
- Higher LDL cholesterol, especially the oxidized form and atherosclerosis
And while most labs classify anywhere between 0.5 and 4 uIU/ml as ‘normal’, research suggests that levels >2.1 may already be suboptimal, contributing to symptoms (R).
Why TSH in normal ranges does not necessarily mean it is optimal
‘Normal’ TSH levels should be between 0.35 – 5.5 (with slight variations, depending on the lab), ‘normal’ free T4 11.9-21.6 pmol/l, normal free T3 3.1-6.8 pmol/l, and normal TPO antibodies < 35 IU/ml.
However, research shows that those markers, for optimal health, should be in much narrower ranges.
Research shows that even while TSH levels A recent study (2022) found that both low- and high-normal TSH levels were associated with increased all-cause and cardiovascular mortality in adults with diabetes (R).
Another study found that in healthy people, the TSH distribution is skewed towards the lower end of the reference range (yet not too low!), with the mean value being around 1.5 uIU/l (R).
Optimal ranges for young and middle aged adults appear to be 0.5- 2.5, or if one wants to be even stricter, 2.1.
Interestingly however, this range moves slightly upwards as one get older, with research indicating that those in 70 and over might want to aim for a TSH of 1.9 – 2.5 (R).
Different research studies into longevity have shown that TSH that is slightly higher than in young people is in fact linked to better longevity, health and a ‘survival advantage’ in older age. More research needs to be done to confirm the exact reasons, however current thoughts are that the aging heart might be less able to handle as much stimulation, and as such benefits from a slightly ‘calmer’ metabolism (R, R).
However, contrary to what some advocate, lower TSH levels aren’t all better, and ideally we keep them in a narrow, ‘middle’ optimal range.
TSH in the low normal range has been linked to
- Increased risk of heart palpitations
- Adverse bone density, including osteoporosis and subsequent fractures (R).
In numerous studies, levels above 2.5 (in the ‘high normal range’) were associated with an increased risk for metabolic and cardiovascular concerns, including:
- Increased cortisol levels – with negative downstream effects on our immune system, increased risk of depression, anxiety and poor cognitive function (R).
- Insulin resistance and an increased risk for the development of metabolic syndrome (R).
- An increased risk of atherosclerosis and cardiovascular disorders, via increased inflammation. This was even found in THS levels as low as >2.1 (R).
- Reduced fertility with decreased AMH and skewed ovarian hormones when TSH is higher than 2.5 (R).
- An increased risk for developing overt thyroid disease, with a higher likelihood of existing thyroid auto-antibodies when TSH was above 2.5 (R).
- Worsening of blood pressure and lipid levels (ie cholesterol, etc) (R)
- Increased risk for non-alcoholic fatty liver disease
- Weight gain
Causes:
Low TSH may suggest hyperthyroidism, which could be due to an autoimmune response (Grave’s disease) or excessive iodine.
High TSH may suggest hypothyroidism, which could be due to
- Inadequate precursor intake (iodine, tyrosine=protein).
- Stress and inflammation disrupting the HPA axis (hypothalamus-pituitary axis), down regulating thyroid output.
- Inadequate methylation and progesterone blocking thyroid production.
- Auto-immune conditions such as Hashimoto’s
Strategy to support TSH levels:
Pinpoint and address the underlying cause such as
- Iodine levels
- Protein intake (tyrosine)
- Stress
- Inflammation
- Autoimmune triggers.
Mirthe
It is my goal to empower you to become the CEO of your health trajectory, preventing and optimising with precision and science backed strategies to live your best life & thrive.
HI, I'M MIRTHE
It is my goal to empower you to become the CEO of your health trajectory, preventing and optimising with precision and science backed strategies to live your best life & thrive.
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