One tree in field

Too many times we see thyroxine treated patients on the ‘set and forget’ setting. Often, they’re taking the same dose they started on a decade or so ago, in spite of weight changes, ageing of course and new comorbidities. They’ve undergone limited monitoring, with just an annual in-range TSH viewed as confirmation of efficacy.  But is it? Many patients’ re-emerging hypothyroid signs and symptoms would suggest not.

A recent Medscape review article of a large study by Gullo et al 2017, identifies another shortcoming in the rudimentary way we ‘replace thyroid hormone’, in all patients but especially in those who’ve had their thyroid removed.

It ‘s kind of not surprising in some ways that the HPT axis is impacted by seasons and temperature, right? In euthyroid individuals, however, this seasonal transition is almost invisible but in the Gullo et al study of over 11K individuals and almost 4K who have no thyroid and therefore rely entirely on replacement, they found the latter, even when their dose of thyroxine remained stable, recorded lower free T4 and T3 levels in colder months and a corresponding rise in TSH!

In winter or during periods spent in a colder climate, the pituitary calls out to these patients’ long-gone thyroid – saying, “Please Sir, Can I have some more?!”

While these T4/T3 changes might be small, the authors comment, for some patients it could be enough to precipitate a hypothyroid state. 

Do your thyroxine treated patients feel worse in winter?

This study doesn’t establish why this abnormal seasonal response happens in thyroxine replaced patients but they do put forward a lot of theories that are worth the read.  This includes the impact that environmental temperature has on the activity of both deiodinase 2 and 3, those critical enzymes that convert our T4 into the real-deal T3 – who would have thought the enzyme activity varies with ambient temerature?!  In euthyroid individuals not on replacement, the activity of  deiodinase type 2 increases in cold climates – giving us more systemic T3 relative to the T4 produced, while the deiodinase type 3 slows down, leading to reduced hypothalamic T3 levels and therefore a tendency towards higher TSH and the pituitary’s reason for saying ‘please sir can I have some more!’ It’s like a seasonal set-point change – we know we need to have more thyroid hormone to warm up! So the big news really is that in thyroxine treated individuals, the suspicion is, deiodinase type 2 activity does not increase as it should – so when they feel the cold thyroxine replaced individuals are not able to ‘turn up the internal heater’ the way the rest of us are.

Let’s face it, truly understanding the thyroid is a lifelong commitment, but with more information coming out all the time…we continue to be in a better position to help so many of our clients affected by suboptimal thyroid health.. I hope this helps again 🙂

Want to know the more about the differences between thyroxine and Natural Thyroid Extract (desiccated gland) replacement? With an increasing number of patients taking a natural replacement path – what do you need to know about the different approaches and how can you best support them with this choice?  While the synthetic option is open to criticism about its inability to provide effective support to every hypothyroid patient, there are some important limitations of NTE  you need to be across as well. Get it all in under 30 mins in Thyroid replacement Strategies – Thyroxine Vs Armour.








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