A female veterinarian is petting a cat on a table. The veterinarian specializes in cats and is providing them with affectionate care.

Thyroid Disease in Cats: Diet and Environment


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Thyroid disease in cats, especially cat hyperthyroidism, is considered one of the most common disorders in middle-aged to older cats. But this disease, although challenging, is not a sentence for diminished quality of life for your fur kid, especially when armed with the right information and support.

Understanding the symptoms, diagnosis, and treatment options will give you the tools to best help your cat. This article covers, in particular, the role of your cat’s diet and environment. Let’s pounce right in …

A vet examines a cat with a stethoscope for potential thyroid disease.

What is thyroid disease?

To understand thyroid disease, let’s first chat about the thyroid gland in cats. Picture it like a little control centre situated in your cat’s neck, right around where their collar would sit. It conducts a whole range of body functions by producing thyroid hormones.

These hormones are the cat’s go-to guys for regulating metabolism – the process of turning food into fuel and energy. So, when your cat’s thyroid is on point, it helps them stay at just the right energy level – not too lazy, but not bouncing off the walls either. It’s all about balance.

Thyroid disease in cats is pretty much when this gland starts acting up. It’s like the gland forgets its job description and either goes into overdrive or pretty much takes a nap, and this can make your cat feel quite off.


There are mainly two types of thyroid diseases that cats deal with:


This is the more common one. It’s like the thyroid gland gets a bit too enthusiastic and starts producing way more hormones than your cat needs.

The result? Your cat’s body goes on fast-forward. They might lose weight even though they’re eating more, have loads of energy (but not the good kind), and generally seem restless or even a bit cranky.


This one’s less common. It’s the opposite situation, where the thyroid decides to slack off and doesn’t make enough hormones. This can make your cat’s metabolism hit the brakes, leading to symptoms like weight gain, lack of energy, or a dull-looking coat.

A gray cat with thyroid disease is sitting on top of a table.

What causes cat thyroid disease?

Thyroid problems in cats, especially hyperthyroidism, can have a few different triggers. It’s a bit of a mystery sometimes, but here’s what we generally know about what causes these thyroid issues:



The environment can play a significant role in thyroid disease in cats. For instance, exposure to flame retardants (such as PBDEs found in household dust) has been investigated as a possible risk factor for hyperthyroidism.

These chemicals are used in many consumer products, including furniture and electronics, and cats can be exposed through grooming after contact with these substances.

Some studies have also looked into whether the type of cat litter used could be associated with an increased risk of hyperthyroidism, although findings have been inconclusive.

Indoor cats might have different exposure levels to certain chemicals or dietary components than outdoor cats, which could influence the development of thyroid disease.

Benign tumours

The most common cause is benign tumours called adenomas on the thyroid gland. These aren’t cancerous, but they’re like overzealous little factories pumping out too much hormone.

Thyroid cancer

Although it’s much less common, thyroid cancer can also cause hyperthyroidism in some cats. This is a more serious condition compared to benign tumors.


It’s thought that there could be a genetic predisposition to the condition, in other words that some cats are born with hyperthyroidism – although specific genetic factors haven’t been identified. Here’s an article on hereditary and congenital conditions if you’re interested in the difference between the two.

Iodine deficiency

It’s super rare since most cat foods have enough iodine. But technically, not enough iodine can make the thyroid lazy.


Some research suggests that certain diets might contribute to the development of hyperthyroidism, although no direct cause-and-effect relationship has been proven. As mentioned, high levels of iodine in cat food have been under investigation as a potential factor. We go more into diet later in this article.


It mostly shows up in middle-aged to older cats, suggesting that the thyroid gland might start malfunction due to age.


Treatment side effects

The most common cause of hypothyroidism in adult cats is the treatment for hyperthyroidism. Treatments such as surgery (thyroidectomy), radioactive iodine therapy, or long-term medication can sometimes reduce thyroid hormone production too much, leading to hypothyroidism.

Congenital disease

Like hyperthyroidism, kittens can be born with it, but it’s pretty rare. Their thyroid glands are either underdeveloped, not developed at all, or unable to produce enough thyroid hormone. This is known as congenital hypothyroidism.

Iodine deficiency

It’s super rare since most cat foods have enough iodine. But technically, not enough iodine can make the thyroid lazy.

Thyroid gland damage

Damage to the thyroid glands caused by illness, injury, or tumours can lead to reduced hormone production. However, this is quite rare in cats compared to dogs and humans.

A cat with thyroid disease is eating food from a yellow bowl.

What are the symptoms of cat thyroid disease?

Whether it’s in overdrive (hyperthyroidism) or taking a snooze (hypothyroidism), your cat might give you some hints that something’s up. Here are the symptoms:


Weight loss: Your cat might lose weight even though they’re eating the same amount or even more. It’s like their body is burning fuel on turbo mode.

Increased appetite: They can turn into a little food vacuum, wanting to eat all the time.

Hyperactivity: They might seem more jittery or active than usual, like they’ve had one too many catnip treats.

Increased thirst and urination: You might notice you’re refilling the water bowl and cleaning the litter box more often.

Vomiting or diarrhoea: Their tummy might not be too happy, leading to some messy situations.

Unkempt appearance: They might not groom themselves as neatly as before, leading to a scruffy or greasy coat.

Increased heart rate: Their heart might be going a bit too fast, which your vet can check.

Behaviour changes: They might seem cranky or just not their usual selves.

Hypothyroidism symptoms

Hypothyroidism is pretty rare in cats, but if it happens, here’s what you might see:

Weight gain: They might pack on some extra pounds without eating more.

Lethargy: Your kitty might seem more like a couch potato, less interested in playing or moving around.

Cold sensitivity: They might seek out warm spots more often or not like the cold much.

Poor coat condition: Their fur might not be as lush or might get a bit matted.

A cat with thyroid disease walking on the street in front of a blue building.

Thyroid disease treatment

Treating cat thyroid disease mainly focuses on getting that overzealous or underperforming thyroid gland back in line. Here’s how vets typically tackle these issues:

For hyperthyroidism

  1. Medication: Anti-thyroid drugs like methimazole can turn down the volume on the thyroid’s hormone production. These meds don’t cure the condition but manage the symptoms pretty well. You’ll need to give them to your cat for life, and regular vet check-ups are a must to keep things balanced.
  2. Radioactive Iodine therapy: This is a more permanent fix. It involves a one-time treatment where your cat gets a small dose of radioactive iodine. Most cats won’t need medication after this, but it’s a bit pricey and involves a short stay at a special facility.
  3. Surgery: Removing the thyroid gland (or the part that’s acting up) can solve the issue, but it’s not super common these days due to the risks and availability of other treatments.
  4. Dietary therapy: Feeding your cat a special diet low in iodine can control the production of thyroid hormones. But, your cat has to eat this food exclusively for it to work (more on this below).

For hypothyroidism

Hypothyroidism is rare and usually a result of treatment for hyperthyroidism. If it happens, treatment might involve:

  1. Thyroid hormone replacement: Similar to humans with hypothyroidism, cats can take a synthetic thyroid hormone to replace what their body isn’t making. It’s like outsourcing the thyroid’s job to a medication.

Regardless of the condition, a key part of treatment is regular follow-ups with your vet. They’ll monitor your cat’s response to treatment and make sure everything’s staying on track. It’s also super important to keep an eye on your kitty at home. Notice any changes in their behaviour, appetite, or weight, and keep your vet in the loop.

A cat drinking from a bowl on the grass.

What cat food is best for thyroid problems?

Choosing the right cat food is crucial when managing cat thyroid disease, especially hyperthyroidism. Here’s how you can approach feeding a cat with thyroid issues:

  • Prescription diets: Vets often recommend special prescription diets for cats with hyperthyroidism. Since the thyroid gland needs iodine to make hormones, limiting iodine helps reduce hormone production.

    Brands like Hill’s Prescription Diet y/d Thyroid Care are designed for this purpose. Remember, if you go this route, it’s crucial that your cat eats only the thyroid care food—no other food or treats—as even small amounts of additional iodine can reduce the diet’s effectiveness.

For cats on medication or post-treatment

  • If your cat is being treated with medication, radioactive iodine therapy, or surgery and the thyroid levels have stabilised, you can generally feed them a normal, high-quality diet unless your vet advises otherwise. The key is ensuring the food is well-balanced and suits your cat’s age, activity level, and overall health.
A siamese cat next to a person's hand.

How long can a cat live with thyroid disease?

With proper treatment and management, a cat with thyroid disease can live a relatively normal life span, often enjoying many happy years even after the diagnosis.

The exact lifespan can vary based on factors like the cat’s overall health, how early the disease was diagnosed, and how well the condition is managed. Here’s a more detailed breakdown:

Insure your cat kid

Whether it’s thyroid disease or something else, our cat kids can get into unforeseen accidents or become ill. You’ll always want to give them a soft landing, so having cat insurance in place is vital. It helps you pay for big and little health bills for aches, scrapes, illnesses and more.

Your pet plan can help pay for X-rays, diagnostics, unexpected vet visits, surgery and, depending on the level of cover you choose, dental bills too! Why wait ’til it’s too late, get award winning pet insurance today.

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