What is an optimal Free T3 level?
The short answer
An optimal Free T3 level is above 3 pg/mL. That is Dr. Peter Attia's number. You can watch him say it below.
Most labs call Free T3 low only under 2.3. So your report can come back normal at 2.7 while you sit under the line he draws.
“if someone's TSH is between about 0.5 and 2.0 and they're free t3 is above 3.0 and their reverse t3 is below 12 I find it very hard to see how they could have hypothyroidism”
Where a number lands, and who said so
- under 2.3 pg/mL Most labs flag this as low
- 2.3–3 pg/mL Normal on most reports. Below optimal Dr. Peter Attia · 7:42 →
- above 3 pg/mL The range Dr. Peter Attia draws
What Free T3 measures
The active thyroid hormone that is unbound and available to your tissues.
The active form does the work in cells. So it can show a problem while the signalling hormone still looks fine.
Checked against MedlinePlus — Triiodothyronine (T3) Tests.
One of the doctors we cite, on why it matters
“if you have um a good T3 level your your cholesterol is in check your memory is good your your metabolism is good you stay thin it helps your hair grow and helps your muscles um prevents muscle aches constipation and even you know improves fertility”
Common questions
What is an optimal Free T3 level?
Above 3 pg/mL, according to Dr. Peter Attia.
What is a normal Free T3 level?
Most US labs print 2.3–4.2 pg/mL. Your report grades you against that range. It exists to catch disease, not to describe your best.
What does your Free T3 number mean?
Under 2.3 pg/mL, your report marks it low. Between 2.3 and 4.2 it prints as normal. Over 4.2, your report marks it high. Where the people we follow draw their own line is above.
Is Free T3 of 2.7 normal?
Your lab will call it normal. Dr. Peter Attia puts the floor at 3 pg/mL, so by that number it is low.
What does the Free T3 test measure?
The active thyroid hormone that is unbound and available to your tissues. The active form does the work in cells. So it can show a problem while the signalling hormone still looks fine.
Where does this number come from?
Dr. Peter Attia, on video. The link above jumps straight to that minute.