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Originally published on 10th October 2016 Last updated on 22nd May 2019
It Can Affect How Much of Your Thyroid Medication You Absorb
It’s well reported, that coffee impacts the absorption of T4-only thyroid medication such as Levothyroxine, which is why thyroid patients need to wait at least an hour after taking their T4 medication before drinking any tea or coffee. 
I personally would avoid all caffeine within an hour of taking any thyroid medication, not just Levothyroxine, to be on the safe side. To get around this, an option could be to take levothyroxine medication at night. Some studies have shown that taking levothyroxine at bedtime may improve absorption. It also allows for you to have your morning cup of coffee without worrying about it affecting your thyroid medication. 
It Can Increase Blood Sugar
Caffeine heavily increases our blood sugar levels when consumed. Blood sugar spikes cause cortisol to shoot up, which can tire out the adrenals and exacerbate hypoglycaemia, Hashimoto’s and ‘adrenal fatigue’. 
I have covered in another post why so many of us with thyroid problems are likely to suffer from blood sugar imbalances, so this is a serious thing to consider and explore. If you get ‘hangry’ (hungry and angry), dizzy, faint and irritable when hungry, you could well have blood sugar imbalances.
It Can Tire Out Your Adrenals
As touched on above, caffeine makes our blood sugar spike, which causes the adrenal glands to pump out more cortisol. Also, when your blood sugar levels drop below normal, sometimes after a spike, your adrenal glands respond by secreting more cortisol. This cortisol then tells the liver to produce more glucose, which brings blood sugar levels back to normal. Doing this repeatedly can cause abnormal cortisol output and can suppress pituitary function. 
Drinking coffee whilst also having ‘adrenal fatigue‘ (note: it is more accurately referred to as hypothalamic-pituitary axis dysfunction) is only adding fuel to the fire and can make this worse.
It Can Damage The Gut Lining and Encourage Acid Reflux
Coffee can irritate the oesophagus or weaken the lower oesophageal sphincter, which prevents the backward flow of stomach contents that causes acid reflux.
Coffee is highly acidic, so it stimulates the release of gastrin and bile. For people with autoimmune conditions, compromised digestion (such as IBS or leaky gut), this can cause further digestive damage to the intestinal lining. This isn’t great for your gut health which is so intertwined with thyroid health and function.
It Can Cause Migraines
Caffeine can trigger migraines and headaches.
Since caffeine narrows the blood vessels that surround your brain, when you stop consuming it, they expand again, and this can cause pain. It’s easy for your body to get used to caffeine, and when you don’t have it in your system, you can have a withdrawal headache or migraine. You may have just one cup a day at work, then on the weekends don’t drink it, and experience caffeine withdrawal headaches or migraines. This is a sign of dependency.
As explained above, the spike in blood sugar caused by caffeine, could also cause headaches.
Some women experience migraines around the time of their period, possibly because of changes in the level of oestrogen and progesterone, and as the below explains, caffeine affects oestrogen levels too.
It Can Contribute to Too Much Oestrogen
Studies have shown that women who consumed at least 500mg of caffeine daily, the equivalent of four or five cups of coffee, had nearly 70% more oestrogen than women who consumed no more than 100mg of caffeine daily (less than one cup of coffee). Tea is not much better as it contains about half the amount of caffeine compared to coffee.
Migraines, heavy periods, PMT, lumpy breasts, cellulite and even breast cancer can be symptoms of oestrogen dominance.
Oestrogen dominance inhibits T4 to T3 conversion, which can be a reason why your thyroid medication isn’t working or helping you to feel better.
It Can Affect The Conversion of T4 to T3
Coffee contributes to oestrogen dominance, and, as explained above, oestrogen dominance inhibits T4 to T3 conversion. Conversion issues with thyroid medication seem very common and can be the reason why your meds don’t seem to be helping with energy, removing hypothyroidism symptoms and more.
It Can Contribute to Insomnia and Poor Sleep
A study showed that 400mg of “caffeine taken 6 hours before bedtime has important disruptive [sleep] effects” though this can be dependent on the individual and their ability to metabolise caffeine. 
It is often recommend that we avoid consuming caffeine after lunch time, in order to promote a better nights sleep.
As explained above, caffeine also often contribute to adrenal issues, and a key sign of adrenal dysfunction includes trouble getting to sleep and/or staying asleep.
All thyroid patients can benefit from going caffeine-free to see if/how it affects them.
People who give up caffeine tend to report better sleep, less headaches, fewer hot flashes, less anxiety, and less hypothyroid and digestive issues.
I realised that caffeine was contributing to my migraines, so I cut it out, and haven’t looked back since.
However, many thyroid patients also state that they feel fine on coffee, so it really can be individual. Coffee is not something that usually needs to be avoided for life by most of us with hypothyroidism or Hashimoto’s. Many of us can enjoy it in reasonable amounts, though may benefit from avoiding it when overcoming adrenal issues or oestrogen dominance, and reintroducing it after these are addressed.
Do you notice any link between caffeine and your health?
You can click on the hyperlinks in the above post to learn more and see references to information given.
There is an online thyroid course: ‘Freedom From Thyroid Fatigue’, which walks you through how to overcome thyroid fatigue and flare up days with a personalised approach. You may benefit from this guidance if you still experience ongoing fatigue and low energy.
Rachel Hill is the highly ranked and multi-award winning thyroid patient advocate, writer, speaker and author behind The Invisible Hypothyroidism. Her thyroid advocacy work includes authoring books, writing articles, her email newsletters, blogging and speaking on podcasts, as well as being a founding board member for the American College of Thyroidology and The WEGO Health Patient Leader Advisory Board. Rachel has worked with The National Academy of Hypothyroidism, The BBC, The Mighty, Yahoo, MSN, ThyroidChange and many more. She is well-recognised as a useful contributor to the thyroid community and has received multiple awards and recognitions for her work and dedication. She has authored two books: ‘Be Your Own Thyroid Advocate‘ and ‘You, Me and Hypothyroidism‘. Rachel is British, but advocates for thyroid patients on a global scale.