Thyroid UK

Best parameters for shift workers

I am now aware issues can be caused by when levo was taken and when test was done!!!!!

I work rolling shifts on a 10 day pattern (2x 7am, 2x 2pm, 2x 10pm 4x off)so take levo between 11 and 1 as only time can guarantee i am awake every day and not clash too much with eating eat sensibly and sleeping. I take at least 4 hours after anything other than water and dont have anything other than water for at least an hour after, so should not be having absorption issues

A previous thread suggested tsh and Ft4 levels follow a rhythm so now i think i need to find out what time would be the optimal time to get tests done to avoid scuppering myself eg does it matter if i am on a rest day and had a decent sleep or have just done a night shift and got up after 4 hours sleep or even stayed up til test time after a night shift.

I am still highly symptomatic (gone up to 17 stone, hair very dry and falling like mad, skin very dry and splitting on hands - I used to have very greasy skin/hair) but after 4 drs have finally managed to find a gp who will actually see you face to face to discuss results and options, encourages you to read up and will actually listen to what you find and not just say 'but you are in the range so life is rosy'.

Can anyone help with what would be best timing (within above constraints and surgery open hours) or is it enough to just pick a time like mid-day and stick to it and dont take levo until after the test any other suggestions also gratefully received. (unfortunately giving up shifts is not an option☹️)

6 Replies

I was doing 12 hour shifts days and nights and I had dinner late evening with very little after midnight. dinner for days at midday. Least disruptionto the digestive system.. However I now believe I neglected getting extra Sun which is required with possible supplement of D3/K2/A also B12/folic acid. Exposure to daylight/night important to follow the daily rhythm. I cant advise on pills.



Levothyroxine can be taken at any time as long as it is taken with water 1 hour before, or 2 hours after, food and drink, 2 hours away from other medication and supplements, and 4 hours away from calcium, iron, vitamin D supplements and oestrogen.

TSH is highest early in the morning so that is the best time for blood tests. Fasting (water only) is helpful too because TSH drops after eating and drinking.


It is the definition of early in the morning that is giving me grief as When i am on days that is 6am but on afternoons i dont get up till 11ish so to me 6 am would be the middle of the night would my body still have done its thing or only be half way there?

I wondered if it was a case of levels were highest for most in the early morning because Most non shift workers normally take their dose early and get tested early after a nights sleep. If i was tested early am after a night shift and no sleep for maybe 20 hours, would there be any difference to a rest day where i had a nice relaxing evening followed by a nice solid 8 hours sleep before testing. alternatively does your sleep have no effect whatsoever it is simply a case that tsh levels are highest 24 hrs after last dose in which case i should test nearer my normal dose time for a true picture.

You also mention tsh dropping after eating, on nights i often need a stiff coffee and something to eat at around 5am would this affect a test done at eg 9am.

I apologise if this is rambly, i know what I'm trying to say but doing it badly due to a mushy brain at the mo!

Is there a good link or book that explains the steps this rhythm follows and how/if things like food or sleep etc effect it (taking as read im not eating or drinking too close the levo) Then i can work out if i need to reorder eating and sleeping times when tests are due, it may even help with symptoms if i can get it right, current patterns evolved to suit a pre hypo me. Everything ive read so far seems geared to normal people not shift workers



TSH follows circadian rhythms so the definition of early morning with respect to blood tests is 7.30am - 9.00am. Fasting generally means nothing but water 8-9 hours prior to the blood test. I posted a link showing the circadian rhythms of TSH and FT3 in my post above.


Your GP is honour bound to read anything you give them.



Really? Can you substantiate that?


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