What is an optimal TSH level?
The short answer
An optimal TSH level is 0.5–2 mIU/L. That is Dr. Peter Attia's number. You can watch him say it below.
Most labs call TSH high only above 4.5. So your report can call 3.3 normal while it sits above where he draws the line.
“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 0.45 mIU/L Most labs flag this as low
- 0.45–0.5 mIU/L Normal on most reports. Below optimal
- 0.5–2 mIU/L The range Dr. Peter Attia draws Dr. Peter Attia · 7:42 →
- 2–4.5 mIU/L Normal on most reports. Above optimal
- over 4.5 mIU/L Most labs flag this as high
What TSH measures
The pituitary's signal telling your thyroid to work harder.
It moves opposite to thyroid output — the signal gets louder as the thyroid falls behind. It is the thyroid test most doctors order first.
Checked against MedlinePlus — TSH (Thyroid-stimulating hormone) Test.
One of the doctors we cite, on why it matters
“the symptoms aren't specific you know you're a little achy you're a little tired you gain a little weight your Skin's a little dry losing a little bit of hair you're maybe sluggish you have trouble to concentrating you're a little depressed”
What are the symptoms of low TSH?
“you're looking at what we call the tsh which is a thyroid stimulating hormone and if that's really really low that means that you're the thyroid is is producing way too much thyroid hormone”
“if TSH is very very low you would be getting a lot of inhibition from these things you would be in a hyperthyroid state”
“if it's slow your whole system slows down if it's fast your whole system speeds up that's hyperthyroid not that common but it can be a problem for some people but low thyroid or hypothyroid function is really common”
About an overactive thyroid.
“when they're being overproduced then you're going to have symptoms that are going to cause you to lose weight feel sweaty have palpitations be anxious have thinning hair lose your hair have thinning nails”
What does a high TSH mean?
“Sluggishness in the morning, trouble getting going, poor concentration memory, low-grade depression, dry skin, horse voice, sitting hair, coarse hair, being very sensitive to the cold, having cold hands and feet, having a low body temperature, a low pulse, maybe muscle pain, weakness and cramps, low sex drive, fluid retention, even high cholesterol.”
“I I my body temperature is low. I gain weight. My hair is falling. I'm very tired. My periods are altered. I don't have energy to do anything. These are all symptoms of hypothyroidism.”
About women going through perimenopause.
“I'll get a lot of blood work around checking her thyroid a lot of things look like menopause right so you know fatigue and night sweats that might be hypothyroidism weight gain hypothyroidism autoimmune disease”
About the mild form, where the thyroid is only slightly underactive.
“a lot of people walk around with subclinical hypothyroidism where it's very kind of minor but has real significant clinical effects and large data sets have shown that it increases your risk of death and heart attacks”
“it is true that patients with hypothyroidism have lower temperature. What's not true is if you have a slightly lower temp you don't have it doesn't mean you have hypothyroidism.”
About mildly underactive thyroid function in older adults.
“studies find that when you're older low grader subclinical hypothyroidism increases the risk of depression four times”
Who is TSH different for?
“Because it's okay at after 50 years if 50 years of age your TSH will increase by one point. Your upper limit of normal will increase by one point every 10 years.”
“So, basically after 50, we should start to make an allowance to go up. So, somebody who's listening to this who's 70, who has a TSH of six, you're totally normal.”
“low thyroid function affects one in five women and one in ten men that's a lot and half of those cases uh they're not diagnosed”
“hypothyroidism is is 10 times more common in women than men. It's really common in the demographic 40 to 60 years.”
About the months after giving birth.
“there is a clinical entity known as postpartum thyroiditis. that is uh the woman will develop hypothyroidism after birth after the giving birth and uh that you know about 50% of the cases the she will remain hypothyroid in other cases the thyroid function will be restored”
What do doctors say about the test itself?
“most doctors just check something called thyroid stimulating hormone or TSH which unfortunately is not a full picture of the thyroid in fact the interpretation of this most of the time is incorrect”
“if your doctor is only looking at your TSH and unfortunately when you go to the doctor's office a lot of the times that's the only lab they've ordered I prefer to order not just the TSH but the free T4 the free T3 and the reverse T3 if I have any concerns about hypothyroidism”
“the the only biomarker we use is TSH. We also use freeT4 levels and that is it uh for the diagnosis uh we make the diagnosis measuring TSH and freeT4.”
“she had been tested a bunch of times but always only with the TSH the thyroid stimulating hormone which is kind of like the go-to test for um you know a lot of the primary doctors in Internal Medicine doctors and it always had been normal it was in the normal range but her TSH had been trending up”
“The antibodies are not diagnostic. the antibodies will tell you, yeah, this is probably an autoimmune process that's happening. They're not needed for the diagnosis.”
Common questions
What is an optimal TSH level?
0.5–2 mIU/L, according to Dr. Peter Attia.
What is a normal TSH level?
Most US labs print 0.45–4.5 mIU/L. Your report grades you against that range. It exists to catch disease, not to describe your best.
What does your TSH number mean?
Under 0.45 mIU/L, your report marks it low. Between 0.45 and 4.5 it prints as normal. Over 4.5, your report marks it high. Where the people we follow draw their own line is above.
Is TSH of 3.3 normal?
Your lab will call it normal. Dr. Peter Attia puts the ceiling at 2 mIU/L, so by that number it is high.
What does the TSH test measure?
The pituitary's signal telling your thyroid to work harder. It moves opposite to thyroid output — the signal gets louder as the thyroid falls behind. It is the thyroid test most doctors order first.
Where does this number come from?
Dr. Peter Attia, on video. The link above jumps straight to that minute.
Where else this number comes up
- “you want to see your TSH kind of below 2 ish and that tells you that your brain is adequately seeing t4 converted into t3” Dr. Peter Attia · 4:45 →