Dr Amir Khan has issued a warning about a potentially "life-threatening" slow heart rate in people with an underactive thyroid and those taking levothyroxine. He shared the alert in a new episode of his podcast, No Appointment Necessary, and posted a clip on his Instagram account on Friday, August 14.
Why an underactive thyroid slows the heart
The NHS GP and ITV resident doctor explained that an underactive thyroid slows bodily functions because the gland no longer produces enough thyroid hormone to regulate energy effectively. Since the thyroid gland releases hormones that control heart rate, a slow heart rate can occur as part of this process.
Dr Amir Khan said that while a slow heart rate is a potential symptom and could be "life-threatening" if a patient becomes "unconscious", patients rarely visit the GP specifically for this. Instead, they often focus on more noticeable issues such as hair loss or constant tiredness.
"When you've got an underactive thyroid, everything just slows down", he said. "So, you get tired all the time, you might get a slow heart rate. Your hair can start to fall out. That's really common as well. Your skin can become very dry. Constipation is a common symptom as well. So, most people don't come in with constipation. They try and manage it themselves through food and things over the counter. They don't know they've got a slow heart rate, but what they do come in with is my hair is falling out or I'm tired all the time."
Who is more likely to get it, and why is it a serious issue?
He also said women are more likely to get an underactive thyroid. Explaining why, the health expert said: "It's just the way your immune systems are modulated and regulated by your hormones that men don't have. And that makes them brilliant at fighting off infections, but not brilliant at switching off when they need to switch off."
Co-host Cherry Healey asked: "Is it life-threatening?" Dr Amir Khan replied with a warning: "It can be life-threatening. If your thyroid hormone levels plummet, your heart could slow right down. You could become unconscious. It is a medical emergency."
He went on to stress that while an underactive thyroid is common, the issue is serious and urged people not to ignore any warning signs, including a slow heart. He said: "People think an underactive thyroid is just, 'Oh, I'm going take my thyroxine tablets, everyone's got it'. But it is serious."
It's possible to have a slow heart rate (bradycardia) even when you're on thyroxine. This might occur if your thyroxine dose is too low to effectively manage your hypothyroidism, if you're just beginning treatment and your body hasn't adapted yet, or if there's another medical issue causing the slow heartbeat.
What is levothyroxine?
According to the NHS, levothyroxine is a medicine used to treat an underactive thyroid. It's only available with a prescription. Levothyroxine is mainly used to treat an underactive thyroid (hypothyroidism). Levothyroxine can help with symptoms of an underactive thyroid including tiredness, weight gain, and low mood.
Dr Amir Khan explained that thyroxine is a synthetic tablet version of the T4 thyroid hormone. When a patient has an underactive thyroid, doctors typically prescribe this medication to replace the hormones the body is no longer producing in sufficient amounts. He said doctors usually begin with a low dose, ranging from 25 to 50 micrograms, and adjust it based on regular blood tests. He also said that while patients take T4 (thyroxine), the body converts it into the active form, T3, as needed.
The NHS says: "You'll have regular blood tests to check you're on the right dose of levothyroxine. Being on the wrong dose can cause side effects, such as feeling or being sick, diarrhoea, headaches or problems sleeping. If you have any side effects, talk to your GP or a pharmacist."
Why is getting the right thyroxine dosage important?
The doctor warned viewers about the importance of managing medication dosages correctly and ensuring patients have regular blood tests. He says finding the correct dose is a "balancing act" between blood test results, the patient's symptoms, and their lifestyle, as requirements can change over time.
He also said that while people on thyroxine can live good lives, their required dosage can change over time due to factors like ageing, pregnancy, weight changes, or exercise. Because these patients are on a fixed dose, they cannot adjust their intake automatically like a healthy thyroid gland would, making ongoing monitoring through blood tests vital.
He said: "People on thyroxine, whether they're on it for an underactive thyroid or a thyroid that's been removed for whatever reason, getting the dose right is really tricky. But also the dose changes through life. Our body will adjust our thyroid doses as we need to, right? Our brain picks it up. It sends more or less messenger down to that thyroid and says, 'Produce more, produce less.' Our body does it willy-nilly every day and we don't feel it. We feel fabulous."
"With people on tablets, when they're on a set dose, if their requirement for thyroxine changes, they might, for whatever reason, there are lots of different reasons. They can't just adjust their dose. They have to wait for their next blood test. They'll have an annual or six monthly blood test and they go, 'Oh, actually you need a bit more or you need a bit less.' And that adjustment of dose isn't as automatic as we do it. And so to say that they live a happy comfortable life. Yeah, they do, but it's hard."
"It's not an easy life to manage that. Lots of people get on with it fine and they're fine because their dose requirements doesn't change. But I think what's really important, and this surprises people, and it's important we say this as doctors when we start people on it, your dose requirement is likely to change as you get older, if you get pregnant, if you put on weight, if you do lots of exercise, our thyroid will adjust all of that. But if if your lifestyle changed, then your hormone, think about all the jobs it's doing, you know, your requirement will change."
