Should You Avoid Dairy if You Have Hashimoto’s Disease?

In the last several months, we’ve examined how certain supplements such as vitamin D, genistein, cordyceps and inositol impact Hashimoto’s thyroiditis. Today, we’re going to investigate how dairy—in the form of lactose—affects Hashimoto’s disease. Specifically, I’m going to be addressing these two points:


1. How avoiding dairy helps Hashimoto’s disease

2. How dairy affects the absorption of thyroid medication

Should You Avoid Dairy if You Have Hashimoto's Disease?


Before launching into our discussion, let’s talk briefly about lactose intolerance and what happens in the body when one has a sensitivity to lactose, the naturally occurring sugar in dairy products.

Lactose intolerance is a disorder of the small intestine that results from reduced lactase enzymatic activity that in optimal situations would break down lactose into the simpler sugars: glucose and galactose. The papers published by Montalto et al. (2006) and Lomer et al. (2007) examined this condition in great depth.

Behind-the-scenes, what you find in lactose intolerance is that lactose cannot be readily digested by the body. Lactose begins to accumulate in the small intestine which then leads to bacterial overgrowth, gas formation and an altered intestinal environment which may cause damage or injury to the intestinal villi. As you may recall from high school biology class, villi are the tiny structures lining the intestinal wall that allow nutrients to be absorbed.

What’s problematic for those with Hashimoto’s disease is that lactose intolerance, by impairing intestinal absorption, could disrupt the circulation of thyroid medication.

This has serious implications so let’s go to the first study that examines how restricting dairy consumption could help Hashimoto’s disease.

The first research article I reviewed was published in the journal Endocrine in 2014 and was entitled “Decrease in TSH levels after lactose restriction in Hashimoto’s thyroiditis patients with lactose intolerance.”

The authors had noticed that existing research on the prevalence of lactose intolerance in patients with hypothyroidism was lacking. There were also no studies on the effect of restricting dairy/lactose consumption in Hashimoto’s patients who took thyroid medication (which we shall refer to as ‘LT4’ moving forward). The authors carried out this study for a twofold purpose:

1. to determine the frequency of lactose intolerance in patients with hypothyroidism and

2. to examine the effects of lactose restriction on thyroid function in Hashimoto’s patients with lactose intolerance.

How was the study done?

Eighty-three patients with Hashimoto’s thyroiditis who had taken L-thyroxine (LT4) over a minimum of three years were initially enrolled. Lactose intolerance tests were then administered to all subjects.

The researchers found that lactose intolerance was diagnosed in 75.9% of the patients with Hashimoto’s. If you think about it, that’s a pretty large percentage of the Hashimoto’s test population.

For this study, patients who used the following medications were excluded:

  • Raloxifene
  • Bile-binding acids
  • Cholestyramine
  • Orlistat
  • Colestipol
  • Proton pump inhibitors
  • Any preparations including iron, aluminum or calcium

Additionally, patients with the following conditions were excluded:

  • Pregnancy
  • Diabetes
  • Celiac disease and/or other related alimentary tract disorders such as occult or overt inflammatory bowel disease
  • Previous bowel resection surgery

The 83 patients were split into two groups: one group consisted of 63 patients with lactose intolerance.

The remaining 20 patients had no lactose intolerance.

Both groups were put on a dairy-restricted diet with particular emphasis in the morning.

The thyroid medication (LT4) was taken while fasting and subjects had to wait one hour before eating.

What lab tests were measured?

Levels of TSH, fT4, calcium and parathormone (PTH) were measured in all study participants both at the beginning and the end of the study.

Over the course of the 8-week study, due to a lack of follow-up of some subjects and constantly changing TSH levels in other patients (hence, fluctuating LT4 dosages), the final study size was reduced to a total of 50 patients with 38 in the lactose intolerance group and 12 in the control group (no lactose intolerance).

What did the researchers find?

The level of TSH markedly decreased in both the euthyroid and subclinical hypothyroid patients with lactose intolerance following the dairy-restricted diet. What was notable was that the level of TSH in patients without lactose intolerance did not change significantly over the 8 weeks.

The levels of PTH, fT4 and calcium also did not change significantly in either group.

What is the significance of the TSH levels dropping dramatically in the lactose intolerant group?

By restricting dairy products (with lactose being the ‘offending’ ingredient), the researchers were able to demonstrate that lactose restriction allows the small intestine’s absorption of thyroid medication to be improved, thereby reducing the need for higher or increasing doses of LT4!

Another implication of the findings is that lactose intolerance really needs to be considered in hypothyroid patients who have experienced the need to increase LT4 doses, those who have had irregular TSH levels and/or those who are resistant to LT4 treatment. If you recall, 75.9% of the patients recruited in this study were found to be lactose intolerant. The researchers determined that restricting dairy has a beneficial effect on Hashimoto’s patients because all of them are dependent on a thyroid replacement medication, whether it’s Armour®, Nature-Throid®, NP Thyroid®, Synthroid®, Levoxyl® or some other brand. The study showed that avoidance of dairy allows enhanced absorption of the medication that is required in Hashimoto’s, therefore reducing the potential for vacillations in TSH levels that would necessitate different doses of thyroid medication to be administered.

The authors were also the first in scientific research to show that there is a high rate of lactose intolerance in patients with Hashimoto’s disease!


A dairy-free diet led to a decrease in the TSH level without the need for alteration in the LT4 dose.

What were some of the weaknesses of the study?

1. The sample size was fairly small with only 38 in the lactose-intolerant group and 12 control patients.

2. The study was of limited duration—only eight weeks. They also attributed the lack of major change in fT4 levels to this relatively short follow-up period. They hypothesized that a more notable change in the level of fT4 could have been observed in a longer-term trial.

So, in this study, the authors found that the level of fT4 did not significantly decrease after lactose restriction even though TSH dropped significantly.

Would this partially contradict the conclusions drawn in this study in any way?

I would tend to say no.

Existing research has supported that hypothyroidism can cause small changes in the T4 level but larger changes in the level of TSH. However, the changes are smaller when the T4 levels started out within the normal range.

The authors of this study went on to explain that the reason for the lack of significant change in the fT4 levels may be that the fT4 levels in the subjects were normal at the beginning of the study. Adding the short study duration makes it plausible why fT4 was not significantly changed.

3. The thyroid medication contained lactose. The authors believed that if a lactose-free thyroid medication were available, the results of the study would have been even more dramatic in demonstrating the beneficial effects of restricting dairy in those with Hashimoto’s who have a medically-necessary dependence on thyroid medication.

Taken as a whole, however, the findings of this study are still truly remarkable because they show the prevalence of lactose intolerance in patients with Hashimoto’s disease and the researchers successfully demonstrated that restricting dairy in the diet led to a decrease in the level of TSH in those patients with lactose intolerance.

The significant implication of this latter finding, according to the authors, is that by lowering the TSH, it may decrease the need for LT4 treatment. Furthermore, the researchers showed that in the case of hypothyroid patients with higher LT4 dose requirements, irregular TSH levels and a resistance to LT4 treatments, lactose intolerance should be considered while making a diagnosis.

The Negative Feedback Loop in Thyroid Disease

I’m going to pause here for a second. For those of you who are joining us for the first time or who have only recently begun listening to the podcasts, I‘m going to touch briefly upon the negative feedback loop which can clarify the relationship between TSH and T4. When you read about TSH levels going down, is that a good thing in Hashimoto’s disease?

The answer is not a simple “yes” or “no”. We have to consider the context in which the TSH levels have decreased. The body always aims for balance as it strives to maintain homeostasis.

The TSH and T4 relationship can often be confusing to people because a lower level of TSH does not correlate to a lower level of circulating thyroid hormone but in fact, the opposite is seen. Explained in other words, in a person with an underactive thyroid gland, the blood levels of T4 will be low, so the TSH level will end up becoming elevated. Essentially, the thyroid has not produced enough thyroid hormone. The pituitary recognizes this via the hypothalamic-pituitary axis and responds appropriately by secreting more TSH (thyroid-stimulating hormone) in an attempt to force more hormone production out of the thyroid.

In this particular study, a lowered TSH meant that the patients were getting more than sufficient levels of the LT4 medication absorbed just by limiting dairy in their diet. By eliminating dairy, absorption of the medication was improved enough that the patients were able to derive full benefit of the medication they were taking. In other words, it was all absorbed. This could have implied that prior to the study, the patients could have been taking more medication than they otherwise would have had to had they not had dairy to interfere with the absorption of the medication. When the subjects in this study cut out the dairy, it allowed them to metabolize the medication that much better—so much so that TSH then went down!

The takeaway message is twofold: first, there is a high prevalence of lactose intolerance in Hashimoto’s thyroiditis patients. Secondly, the researchers demonstrated that restricting dairy leads to a decrease in TSH levels signifying that whatever LT4 one was taking was more than sufficient, therefore exerting a beneficial effect on those with Hashimoto’s disease.

How Dairy Affects the Absorption of Thyroid Medication

The second article I reviewed was published in The Journal of Clinical Endocrinology Metabolism in 2014 entitled, “Systematic Appraisal of Lactose Intolerance as Cause of Increased Need for Oral Thyroxine.”

The researchers aimed to assess the replacement T4 dose required in hypothyroid patients with lactose intolerance.

With lactose intolerance, it’s not just the symptoms of poor digestion (e.g., diarrhea, gas, abdominal cramps, bloating) that are a concern. In some cases, there can be a severe resistance to oral LT4 treatment which then requires a person with Hashimoto’s disease to take more medication than what the TSH level might indicate in a patient on the day of his or her lab draw. Without the important realization that lactose intolerance could be interfering with the absorption of medication, we could have people with Hashimoto’s thyroiditis walking around, taking the dose of LT4 based on their last TSH lab reading, thinking they’re getting what they need when in fact, they are still exhibiting hypothyroid symptoms because their bodies are not getting enough thyroid hormone via the daily dosage. That is a pretty serious consideration.

How the Study was Done

For the test group, 49 Hashimoto’s thyroiditis patients were recruited of which 48 were females and one male. All suffered from lactose intolerance. Fifteen patients were subsequently excluded which left a test group sample size of 34 patients.

Sixty-eight patients (of which 61 were females and seven were males) were recruited for the control group. They also had Hashimoto’s disease but no lactose intolerance.

What were the Eligibility Requirements of the Patients?

1. All were receiving replacement treatment with levothyroxine (LT4) for Hashimoto’s thyroiditis

2. Patients were confirmed lactose intolerant by a positive lactose hydrogen breath test

3. Patients had been non-compliant with a lactose-free diet based on a questionnaire

Patients with the following conditions or history were excluded:

  • Pregnant or lactating
  • Use of iodine-containing substances and/or diet creams or pills;
  • Treatment with drugs interfering with LT4 absorption and action, including estrogens
  • Those already on a lactose-restricted diet and/or using exogenous lactase.
  • The presence of other GI diseases to avoid bias in the assessment of T4 malabsorption

What Lab Tests were Done?

  • Free T4 (fT4)
  • TSH
  • Anti-TPO Antibody

All patients recruited for the study took their thyroid medication under fasting conditions with a minimum of 1 hour before eating or drinking.

The patients were given a questionnaire to examine their dietary habits and how much dairy they were consuming on a regular basis. They were also asked about any symptoms of lactose intolerance.

All patients were initially treated with a similar LT4 dose to obtain the same target TSH (0.5–2.5 mU/L). What happened next was that the dose was progressively increased until the therapeutic goal had been achieved in at least two consecutive measurements in those patients who did not reach the expected TSH.

What did the Researchers Find?

In the control group, the target TSH was obtained in all patients after 5 ± 2 months of treatment.

In patients with lactose intolerance similarly treated, only 5 of 34 patients reached the expected TSH in a similar period of time (4 ± 2 mo).

What’s really notable is that the remaining 29 lactose intolerant patients failed to achieve the target TSH despite a higher LT4 dose. They finally did reach the point of “pharmacological thyroid homeostasis” at a median T4 dose of 1.81g/kg/d.

What Does All of This Mean?

In 23 patients with isolated lactose intolerance, a median LT4 dose of 1.72g/kg/d had been required to attain pharmacological thyroid homeostasis. This dose is significantly higher when compared with that observed in the control group and also different from the one measured in those patients with lactose intolerance plus other GI disorders.

What was observed by the researchers was that the dose of LT4 required to reach the target TSH was higher in hypothyroid patients who had both Hashimoto’s disease and lactose intolerance than in patients with just isolated Hashimoto’s. In hypothyroid patients with lactose intolerance, the LT4 dose had to be increased by almost one-third to obtain the therapeutic goal!! Additionally, the presence of Hashimoto’s, lactose intolerance plus further GI disorders almost doubled the increased LT4 need!

The authors pointed out, however, that there were five patients with lactose intolerance who did not show decreased LT4 absorption. They could not fully explain how that came to be except to qualify the results as differences in an individual’s degree of lactose intolerance, the co-ingestion of others foods, the residual lactase activity and the unique gut microbiota composition in each of those patients.

From a practical standpoint, the researchers pointed out how adhering to a lactose-free diet could really be a challenge because lactose is added as a preservative in many foods and in medications including thyroid replacement.


The authors of this second study demonstrated that lactose intolerance significantly increased the need for oral LT4 in hypothyroid patients. They point out that when doses of medication start fluctuating, it’s prudent for physicians to suspect unrecognized lactose intolerance in hypothyroid patients.

Final Thoughts

These two studies have definitively revealed that for Hashimoto’s thyroiditis patients, restricting dairy in the diet may help with one’s treatment of the disease by lowering TSH levels and enhancing absorption of whatever thyroid medication one is taking. This precludes the potential for fluctuating TSH levels (higher than expected) and lower circulating levels of thyroid hormone in the body depending on how much dairy a Hashimoto’s patient has consumed from one day to the next.

With a higher TSH and lower levels of thyroid hormone, patients would need to modify the dosage of thyroid medication due to malabsorption from lactose intolerance. Ultimately, the diet that one follows is an individual choice but the studies discussed today would point to the restriction of dairy products as something to consider given the high prevalence of lactose intolerance in those with Hashimoto’s thyroid disease.

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