Optimising Thyroxine absorption

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Thyroxine is one of the most widely prescribed medications worldwide, and yet many patients take this common medication incorrectly, meaning they’re not making the most of their daily dose. Many foods, supplements, medications and other factors can interfere with the absorption of Thyroxine, so it’s essential to discuss these with a healthcare professional when first commencing thyroid hormone replacement, to ensure optimal absorption - essentially, so you can get the most out of your thyroid medication. For those who’ve been on the thyroid bandwagon for a while - if your required Thyroxine dose keeps increasing for no discernible reason, I’d encourage you to review these factors with your healthcare provider as well, to determine whether an absorption issue might be to blame.

By optimising absorption, individuals can better maintain healthy thyroid hormone levels on the lowest dose possible required for their situation. For this reason, I’ve put together a blog on the topic below, exploring some of the common factors that can impair thyroid hormone absorption.

Food (and Drinks)

Thyroxine is mainly absorbed in the small intestine, specifically, two parts of the small intestine called the jejunum and ileum. Depending on the patient, it is estimated that 75-80% of Thyroxine is absorbed into circulation when taken on an empty stomach, however, the presence of food in the stomach can significantly reduce this. Whilst almost all foods have the potential to impair Thyroxine absorption, some are notoriously detrimental, including coffee, soy products, walnuts and dairy, as these foods contain substances (such as tannins or calcium) which further inhibit the uptake of Thyroxine. It’s important to remember that drinks can be just as detrimental to Thyroxine uptake as well, and a common offender I see is a morning cup of tea or coffee. Just like food, these need to be kept well away from Thyroxine. Thyroxine levels peak in the blood about two hours after absorption, or slightly longer in hypothyroid patients. Low stomach acid, which can be associated with certain medical conditions or medications, can also reduce the absorption of Thyroxine from the gut, so I’ve discussed this in more detail below.

Overall, it is recommended to take Thyroxine on an empty stomach, at least 30 minutes before any food (but preferably 60 minutes if possible). Those who wait at least two hours are likely to experience even better absorption than those who only water 30-60 minutes, so if this is feasible for you, it’s definitely something you could discuss with your healthcare provider.

As not everyone is able to wait 1-2 hours before eating after taking their thyroid medication, some of my patients also find it helpful to take their Thyroxine at 3 or 4 AM, if they regularly wake up at this time to go to the bathroom (or feed the baby!). In most cases, this allows a good 2-4 hours before they have breakfast, meaning they can wake in the morning and enjoy their breakfast as usual, without having to wait. Some of my patients have even been able to move to a lower dose of Thyroxine (with their doctor’s guidance), simply by delaying the time between which they take their medication and when they first have something to eat.

Supplements

Many supplements, especially minerals like iron and calcium, can interfere with Thyroxine absorption in the gut, reducing its uptake into the bloodstream. For this reason, individuals should take their Thyroxine a MINIMUM of four hours away from such supplements, or foods containing high amounts of these nutrients (like dairy or calcium-fortified products). In addition to calcium and iron, other substances known to impair Thyroxine absorption include fibre supplements (like slippery elm or wheat fibre), chromium, activated charcoal and certain medications (which I’ll discuss below). It is believed many of these supplements bind with Thyroxine in the gut, forming an insoluble complex that can’t cross the gut wall into the bloodstream.

Interestingly, vitamin C appears to be one of few substances that actually improves Thyroxine absorption. Research suggests taking your Thyroxine with vitamin C improves T4 uptake and reduces TSH level. It is believed this is because vitamin C helps reduce the pH of the stomach, increasing stomach acidity which in turn facilitates improved Thyroxine absorption. Taking vitamin C with Thyroxine seems to be particularly beneficial for patients with compromised digestive function, such as those with gastritis or some of the other conditions listed below. Of course, prior to taking vitamin C with your Thyroxine, you should seek the advice of a qualified healthcare practitioner.

Other Medications

Like supplements, there are MANY medications that are known to impair Thyroxine absorption, and this is why most medications should be taken away from your Thyroxine, unless you are specifically advised by a doctor or pharmacist otherwise.

Some of the main offenders for impairing Thyroxine absorption are antacids, including both over-the-counter and prescription medications such as QuickEze, Gaviscon and Omeprazole (Losec). This is, in part, because antacids raise the pH of the stomach, making the gastric environment less acidic. As Thyroxine is absorbed best in an acidic environment, absorption is subsequently reduced.

Other medications known to impair Thyroxine absorption include cholestyramine and bile acid sequestrants, laxatives, statins, Sucralfate and Cimetidine, via various mechanisms. If you take other medications in addition to your Thyroxine, make sure to check with your doctor or pharmacist by how much you need to separate the two, so as to not impair Thyroxine uptake.

Medical Conditions

Lastly, there are many medical conditions which can result in impaired Thyroxine absorption and as a result, many patients with such conditions require a higher dose to maintain healthy thyroid levels. For example, any condition which results in malabsorption has the potential to impair Thyroxine uptake, including coeliac disease or inflammatory bowel disease. H.pylori infection, chronic gastritis, bowel resection, lactose intolerance, liver cirrhosis, congestive heart failure and certain intestinal parasites can also result in impaired absorption. Individuals over the age of 70 also appear to experience slight decreases in Thyroxine absorption, along with alterations in thyroid hormone metabolism (such as increased reverse T3 formation) which must be accounted for in their care.

The good news is, in many cases, improving the health and function of the gastrointestinal tract can improve Thyroxine absorption. For example, coeliacs who have been on a strict gluten free diet for sufficient time can have similar absorption rates to non-coeliac individuals, and treatment for H.pylori infection can restore Thyroxine absorption to previous levels. Similarly, I’ve worked with many patients with gastritis or inflammatory bowel disease, to support the health, function and repair of their digestive tract, which in turn, may facilitate improved Thyroxine (or nutrient) uptake.

Storing Your Thyroxine

Thyroxine is a somewhat ‘fragile’ medication, in that it can easily become damaged by heat, sunlight and humidity. For this reason, most brands of Thyroxine in Australia need to be kept in the fridge for long-term storage, and individuals are advised that they can keep a single blister strip of tablets out of the fridge for 14-21 days, at no more than 25°C. Any medication that has been unrefrigerated for longer than this should be discarded. It must also be emphasised that these tablets should not be stored in a warm room, and need to be kept out of sunlight (meaning a sunny bedside table or bedroom window sill is not a good place to store them). You should also avoid keeping them in damp or humid rooms such as a bathroom, as steam from the shower can damage the medication. Eltroxin is a shelf-stable version of Thyroxine that does not need to be refrigerated, however it must still be stored at <25°C, away from heat, sunlight and humidity.

Another important thing to take note of is the expiry date on your Thyroxine. Typically, Thyroxine has an expiry date of one year from the date of manufacture. For most people, this won’t be a problem, but if you only take your medication every second day and there’s 200 tablets in a box, it’s likely the contents will expire (and thus lose potency) prior to you finishing the medication. In this case, the expired medication should be discarded (note: it’s always a good idea to talk to your pharmacist about the best way to discard unused medications).

Key Tips to Improve Thyroxine Absorption

  • Take your Thyroxine at least one hour away from food or drinks like tea and coffee (or ideally more, if you can manage it).

  • Ensure certain supplements such as calcium or iron tablets are taken at least 4 hours away from Thyroxine.

  • Speak to your doctor or pharmacist about other medications you are taking, and how far away from Thyroxine you should take them so as to not inhibit absorption.

  • Investigate or consider potential medical conditions that might be impairing your absorption of Thyroxine, so you can address them where possible.

  • Talk to your healthcare provider about whether taking your Thyroxine with a small dose of vitamin C may be helpful.

  • Ensure your Thyroxine is stored correctly and not used past its expiry date.

  • Regularly check your thyroid function and if your dose keeps increasing, consider whether any of these factors might be to blame.

The Takeaway Message

Ultimately, there are many factors and substances that can interfere with thyroid hormone absorption, and these should always be discussed with an individual when they are first prescribed the medication. As a naturopath, I’ve worked with patients who have always taken their Thyroxine with a morning coffee, and yet when they stop doing this, we’ve been able to work with their doctor to lower their dose. I’ve also worked with patients with poor absorption due to conditions like gastritis or coeliac disease, and once we’ve started working on the problem, we’ve found their absorption has improved. For this reason, if any of these factors are relevant to you, it’s important to know that changing your habits may increase your thyroid hormone absorption, and therefore you should discuss this with a healthcare professional first so they can monitor your thyroid function and adjust your dose if necessary.

Niki x