What is the recommended daily dose of levothyroxine (T4) for a 32-year-old male with borderline thyroid function, cold hands and feet, psoriasis, eczema, and slow progress in strength training, with a history of elevated antibodies and autoimmune conditions?

Should You Start Levothyroxine (T4)?

You should not start levothyroxine based on your current thyroid function tests, as your TSH (3-4 mIU/L) and free thyroid hormones are within normal reference ranges, and your symptoms are not explained by thyroid dysfunction. 1

Why Your Thyroid Function Does Not Warrant Treatment

Your thyroid parameters do not meet criteria for levothyroxine therapy:

• TSH 3-4 mIU/L is normal – Treatment is only recommended when TSH is persistently >10 mIU/L or for symptomatic patients with TSH 4.5-10 mIU/L who have positive thyroid antibodies 1
• Your TPOAb and thyroglobulin antibodies are currently negative – This removes the autoimmune rationale that might justify treatment at borderline TSH levels 1
• Free T4 (16 pmol/L, reference 12-22) and free T3 (5.8 pmol/L, reference 3.1-6.8) are solidly mid-range – These values definitively exclude both overt and subclinical hypothyroidism 1
• Your previous positive thyroglobulin antibodies (5 years ago) that have now normalized suggest resolved transient thyroiditis – This is not an indication for lifelong treatment 1

Your Symptoms Are Not Thyroid-Related

The constellation of cold extremities, slow muscle gain, and fatigue with normal thyroid function tests points to alternative explanations:

• Cold hands and feet at 21°C with normal thyroid hormones – This is not hypothyroidism; consider autonomic dysfunction, poor peripheral circulation, or low muscle mass affecting thermogenesis 1
• Temporary improvement after strength training – This pattern suggests vascular/circulatory issues rather than hormonal deficiency, as exercise transiently improves peripheral blood flow 1
• Slow strength training progress with testosterone 460 ng/dL – While this testosterone is low-normal for age 32, it's more likely contributing to your training plateau than thyroid function 1
• FSH 3.4 mIU/L is normal – This rules out primary hypogonadism, but your testosterone/FSH ratio suggests possible secondary hypogonadism worth investigating separately 1

Why Starting T4 Would Be Harmful

Initiating levothyroxine with normal thyroid function carries significant risks:

• Iatrogenic hyperthyroidism occurs in 14-21% of treated patients – This increases risk for atrial fibrillation (5-fold increased risk with TSH <0.4 mIU/L), osteoporosis, fractures, and cardiac complications 1
• Approximately 25% of patients on levothyroxine are unintentionally maintained on excessive doses – This leads to TSH suppression with attendant cardiovascular and bone risks 1
• Starting unnecessary thyroid hormone creates lifelong dependency – Once started, distinguishing between true hypothyroidism and medication-induced suppression becomes difficult 1
• Your symptoms would not improve – Since they're not thyroid-mediated, you'd experience medication risks without benefit 1

What Actually Needs Investigation

Your symptom complex warrants different workup:

For cold extremities and poor circulation:

• Raynaud's phenomenon screening (given your psoriasis/autoimmune history) 2
• Peripheral vascular assessment
• Autonomic function testing
• Iron studies are adequate (ferritin 92 µg/L, iron 134 µg/dL), ruling out anemia 1

For slow muscle gain and suboptimal testosterone:

• Repeat morning testosterone with SHBG and calculated free testosterone 1
• LH measurement to distinguish primary vs. secondary hypogonadism (your FSH 3.4 suggests possible central issue) 1
• Prolactin level (can suppress gonadotropins) 1
• Consider endocrinology referral for possible testosterone replacement if confirmed low on repeat testing 1

For psoriasis and eczema:

• These autoimmune conditions increase risk of other autoimmune diseases, but your negative antibodies and normal thyroid function exclude autoimmune thyroid disease currently 2
• The previous positive thyroglobulin antibodies that normalized suggest transient thyroiditis, not Hashimoto's requiring treatment 1

For gastrointestinal symptoms (meteorism, sticky stools, constipation):

• Your negative celiac testing and normal fecal elastase are reassuring 1
• Consider small intestinal bacterial overgrowth (SIBO) breath testing
• Evaluate for bile acid malabsorption
• These GI symptoms could affect nutrient absorption despite adequate intake 1

If You Were to Start T4 (Which You Shouldn't)

Hypothetically, if treatment were indicated, the dosing would be:

• Full replacement dose: 1.6 mcg/kg/day – For your 78 kg weight, this equals approximately 125 mcg daily 1, 3
• However, starting dose for age 32 without cardiac disease would be 50-75 mcg daily, titrated by 12.5-25 mcg every 6-8 weeks based on TSH response 1, 3
• Target TSH would be 0.5-4.5 mIU/L with free T4 in upper half of reference range 1, 3

But this is entirely inappropriate for you – Your TSH 3-4 mIU/L with normal free hormones means you're already euthyroid and would become hyperthyroid on this dose 1

Critical Pitfall to Avoid

Do not pursue levothyroxine based on functional medicine concepts about "optimal" TSH or reverse T3 – Your TSH 3-4 mIU/L represents normal thyroid function, and the geometric mean TSH in disease-free populations is 1.4 mIU/L, meaning your value is physiologically normal 1. Studies show reverse T3 testing adds no clinical value in patients on levothyroxine and should not guide treatment decisions 4, 5.

Recommended Action Plan

1. Accept that your thyroid function is normal – Recheck TSH and free T4 only if new symptoms develop or in 12 months 1
2. Pursue testosterone evaluation – Morning total testosterone, SHBG, LH, prolactin 1
3. Address circulation issues – Vascular medicine or rheumatology consultation for cold extremities with autoimmune history 2
4. Optimize training and nutrition – Consider sports medicine consultation for plateau despite adequate macronutrients 1
5. Continue monitoring vitamin D (50 ng/mL) and B12 (400 pg/mL) – Both are adequate but on lower end; consider modest supplementation 1