Medically reviewed by
Dr. Katie Rothwell, ND, a licensed Naturopathic Doctor with clinical focus in thyroid conditions and Hashimoto's disease through The College of Naturopaths of Ontario, Canada.
Depending on the thyroid condition you may have, your health professional will either encourage a dairy-free diet or recommend dairy products in your everyday diet. The relationship between dairy products and our thyroid is a complex and confusing one, which makes your choices in diet a multifactorial decision.
Dairy products contain a sugar called lactose. You often hear about people being lactose-intolerant. This means their small intestine does not produce a digestive enzyme called lactase. Without lactase, your body cannot break lactose down so it can be absorbed by your body. This inability to absorb the lactose causes symptoms like bloating, abdominal pain, and uncomfortable situations in the bathroom.
Typically, you are born with the ability to produce lactase, but as you get older you lose it. Research shows that lactose by itself does not show any direct benefit or harm to our thyroid’s ability to function, but there are many factors to consider in their relationship. This includes factors such as iodine, calcium intake, lactose intolerance, and dietary modifications and restrictions.
How Dairy Products affect your Absorption of Thyroid Medication
Despite nearly 68% of the world’s population being lactose intolerant or lactose malabsorption, cow’s milk is a staple in many North American households and is often advised in dietary guidelines. Lactase persistence is a mutation that allows humans to continue digesting lactose into adulthood. Those without this ability will experience stomach pains and digestion problems, but consider that this is normal! It’s so normal that it is extremely important to consider the effects of dairy indigestion on the absorption of your thyroid medication.
In North America, thyroid patients are most commonly prescribed levothyroxine, a monotherapy or single-drug therapy used for hypothyroidism. When prescribed, patients are advised to take levothyroxine at least 1 hour before their first meal for the day or 4 hours from taking another medication or supplement.
Previous research shows that calcium supplements can alter the effectiveness of thyroid medication and the body’s ability to absorb it, so there must be similar effects when you drink or eat dairy products, right?
A pharmacokinetic study done by Chon et al. measured the serum total thyroxine (TT4) levels of 10 healthy volunteers after consuming 2% fat cows’ milk. TT4 refers to the total amount of thyroxine thyroid hormone (T4) present in the volunteer. Having too much or too little T4 is used to identify thyroid disease. What this study found was that consuming cows’ milk while taking oral levothyroxine reduced the medication’s absorption in the body. In other words, milk was interfering with the thyroid medication likely due to its calcium content. It is recommended that patients take their levothyroxine on an empty stomach to optimize its absorption in the gastrointestinal tract.
Lactose and Autoimmune Thyroid Diseases
Autoimmune thyroid diseases such as Hashimoto’s thyroiditis and Graves’ disease happen when your immune system is in hyperdrive and accidently attacks your thyroid gland. This leads to painful inflammation of the thyroidal tissue. We know that people with lactose intolerance cannot break down lactose for the gastrointestinal tract to absorb. This suggests that lactose intolerance could potentially increase your risk for autoimmune thyroid diseases as it compromises your gut and intestines function and permeability and disrupts your healthy gut bacteria. When this happens, gut bacteria and waste or toxins in your gut can escape into your bloodstream and trigger an immune response.
Another study focused on Hashimoto’s thyroiditis and lactose intolerance. Hashimoto’s thyroiditis is controlled using synthetic levothyroxine to maintain a patient’s level of thyroid stimulating hormone (TSH). TSH is necessary for regulating your thyroid function and the growth of thyroid cells. What the study found was that patients who were lactose intolerant but continued to consume dairy products would need a higher dosage of levothyroxine.
This suggests that high calcium intake through dairy products, may interfere with thyroid hormone production and absorption but also your medication’s efficiency. Due to this, lactose intolerance is an important factor to consider when prescribing thyroid medication especially in Hashimtoto’s thyroiditis patients.
Can Dairy Products be Beneficial?
While there is no strong evidence to suggest that dairy products increase the risk of thyroid diseases, dairy products are a good source of iodine. Iodine is a mineral we need to maintain normal thyroid function and produce hormones. These hormones help regulate biological processes such as metabolism and growth.
In the United States, cows’ milk is a primary source of iodine, so does this mean milk and dairy products can also benefit people with thyroid diseases? Potentially. Without iodine, your TSH levels will be higher than normal and you won’t be able to produce enough thyroid hormones. This is when you start showing signs of hypothyroidism which puts you at risk of Hashimoto’s and Grave’s disease as well as thyroid cancer.
Some studies argue that consuming dairy products high in iodine is beneficial for thyroid health. Consider that dairy products could help prevent thyroid disorders rather than treat them. However, dairy also contains calcium. High levels of calcium will interfere with iodine’s ability to produce thyroid hormones because calcium is going to bind to iodine. This reduces how much iodine is available to be used to synthesize thyroid hormones. On the other hand, excessive iodine consumption can lead to hyperthyroidism as too many thyroid hormones are produced.
So…there needs to be a middle ground or a better iodine alternative. Fortunately, there is an alternative source of iodine. Salt iodization is the recommended public health measure to combat iodine deficiency in North America, primarily in the United States. It also provides ideal amounts of iodine for breastfeeding women and infants. So, we don’t need to rely on dairy products for adequate iodine intake. You can also get iodine from foods like tuna, cod, seaweed, eggs, and iodized salt.
So, while dairy products are an excellent source of iodine which helps maintain and regulate the production of thyroid hormones, you have other alternatives for iodine intake. On the other hand, studies suggest that high calcium intake will interfere with thyroid hormone production and absorption, especially in people with iodine deficiency. This calls for a balanced diet. You can’t have too low or high calcium intake nor can you be iodine deficient or excessive. Your overall dietary pattern plays a major role.
To conclude, consuming dairy products that are high in iodine could be beneficial for thyroid health; however, the effects of other nutrients in dairy products, such as calcium, are shown to have a greater risk of worsening your symptoms and negatively impacting thyroid function. This is why it is important to consult with a healthcare professional or registered dietitian for personalized advice on thyroid health and nutrition.
- Lactose intolerance means your small intestine does not produce a digestive enzyme called lactase. Without lactase, your body cannot break down lactose, which causes bloating, abdominal pain, and digestive problems.
- Dairy products are an excellent source of iodine which helps maintain and regulate the production of thyroid hormones, but high calcium intake can bind to iodine and prevent it from being used to produce these hormones.
- Calcium supplements and dairy products can negatively alter the effectiveness and absorption of thyroid medication like levothyroxine.
- It is recommended that patients take their levothyroxine on an empty stomach to optimize its absorption in the gastrointestinal tract.