Optimal Ranges
What is the optimal range for TSH?
Clinical (NHS) Range
0.4-4.0 mIU/L
mIU/L
Performance-Optimised Range
1.0-2.0 mIU/L
mIU/L
| Range | Value | Unit |
|---|---|---|
| Clinical (NHS) reference range | 0.4-4.0 mIU/L | mIU/L |
| Performance-optimised range | 1.0-2.0 mIU/L | mIU/L |
The clinical range defines what is considered medically “normal” — broad enough to cover 95% of the population. The performance range reflects where research and clinical experience suggest most people feel and function at their best. A result in either range suggests typical status and is not a diagnosis; any individual reading should be interpreted by a qualified clinician.
Why It Matters
Why TSH matters for performance
The thyroid is the body's metabolic thermostat. Even mildly elevated TSH — subclinical hypothyroidism — can cause fatigue, weight gain, cold intolerance, and depression that is frequently misattributed to ageing or overtraining. For men, thyroid dysfunction also impacts testosterone production and cardiovascular health. Standard clinical ranges for TSH are very broad (0.4-4.0 mIU/L), meaning you can be symptomatic at 3.5 and be told everything is 'normal'. Functional optimisation aims for a tighter range where most people feel their best.
Symptoms
What are the symptoms of low or high TSH?
Low / Deficiency
- Low TSH (hyperthyroid symptoms):
- Unexplained weight loss
- Rapid heart rate and palpitations
- Anxiety and tremors
- Heat intolerance and sweating
High / Excess
- High TSH (hypothyroid symptoms):
- Fatigue and sluggishness
- Unexplained weight gain
- Cold intolerance
- Dry skin and hair loss
- Depression and brain fog
- Constipation
Dietary Sources
Which foods support TSH levels?
Supplementation
How do you improve TSH levels?
Selenium (200 mcg/day as selenomethionine) is the most evidence-based thyroid support nutrient — essential for T4 to T3 conversion and thyroid peroxidase function. Iodine supplementation (150-300 mcg/day) only if deficiency is confirmed — excess iodine can worsen thyroid conditions. Zinc (15-30 mg/day) supports thyroid hormone synthesis. Avoid soy isoflavones and excessive cruciferous vegetables if thyroid function is compromised. If TSH is persistently above 4.0, GP referral is recommended.
Testing
How is TSH tested in the UK?
TSH is measured from a blood sample. With Helvy, that means a finger-prick kit taken at home and posted to a UKAS-accredited UK laboratory, with results in around 5 days, reviewed by a qualified clinician. Your result is reported against both the clinical range (0.4-4.0 mIU/L) and the performance-optimal range (1.0-2.0 mIU/L), so you can see not just whether you are “normal” but whether you are optimal. If you make a change, retest after 8-12 weeks to confirm it worked.
Research
Key study
Selenium supplementation in patients with autoimmune thyroiditis
Toulis KA, Anastasilakis AD, Tzellos TG, et al.
Thyroid (2010)
DOI: 10.1089/thy.2009.0351Related Biomarkers
Related Guides
Explore TSH in depth
Test your TSH levels
TSH is included in the Helvy 50+ biomarker panel. Get your results in 5 days with a personalised protocol.
Order Your TestThis content is for educational purposes only and does not constitute medical advice. Your data suggests areas for optimisation, but any concerns should be discussed with a qualified healthcare professional. If your results flag values outside safe ranges, we recommend consulting your GP.