Is there a thyroid diet?

When we receive a diagnosis of a thyroid condition, it is natural that we look for ways to improve our lifestyle. This might be to reduce symptoms, enhance our response to prescribed medication or simply to try to return to ‘normal.’ Looking at the food and dietary supplements we consume is one of the obvious starting points.

Marian Ludgate, Prof Emerita, Cardiff University School of Medicine and Mr Jonathan Hayes, registered dietitian, NHS Lothian assess the available evidence on foods and supplements and their effect on thyroid health

Content overview

Diet

Brassicas

Kelp

Soya

Supplements

Biotin (vitamin B7)

Calcium

Carnitine

Ginger

Iodine

Iron

Lemon balm or Melissa Officinalis

Magnesium

Resveratol

Selenium

Vitamin B12

Vitamin D

Zinc

Always take the recommended dose

Further reading

Diet

Many websites offer advice on what foods to eat or not eat with thyroid disease. However, there are no specific foods or dietary supplements that you can use to treat your thyroid disorder. It is important to eat the right variety of foods in the correct proportions. Having a balanced diet is the best way to ensure your body gets all the nutrients it needs.

The NHS Eatwell Guide recommends you should try to:

• eat at least five portions of a variety of fruit and vegetables every day
• base meals on higher fibre starchy foods like potatoes, bread, rice or pasta
• have some dairy or dairy alternatives
• eat some beans, pulses, fish, eggs, meat and other protein
• choose unsaturated oils and spreads, and eat them in small amounts
• drink plenty of fluids (at least 6 to 8 glasses a day)
• avoid processed foods and reduce sugar intake

There is also increasing evidence that having diverse gut bacteria is associated with better overall health. A diet containing fresh, whole foods, mainly from plant sources like fruits, vegetables, legumes (plants that have their seeds in a pod, such as chickpeas, lentils and edamame), beans, nuts and wholegrains and that avoids highly processed foods can promote a healthy microbiome. At this stage, there is not enough evidence about the role of gut bugs and how they affect thyroid function although some research has been undertaken.

As is often the case, results are clearer in mouse models, using mice that are genetically identical, all female, the same age and fed the same food and water, than in humans with the same condition, who display none of these characteristics. In our mouse model of Graves’ disease (GD)/Graves Orbitopathy (GO) we found a clear connection between certain gut bacteria and disease symptoms; treatments to change the microbiome influenced the induced GD/GO. Antibiotics improved disease whilst faecal material from people with GD/GO made it worse. Although probiotics increased white blood cells with anti-inflammatory properties, some GO symptoms were aggravated. 

The gut microbiome has also been shown to be less diverse and less ‘healthy’ in people with GD/GO but there is wide variation in the changes reported in different geographic regions [ii] (ref Biscarini), reflecting divergent diets and lifestyles. Consequently, it is too soon to recommend a particular antibiotic, prebiotic (fibre-rich foods) or probiotic to treat – or even help to prevent- GD/GO and other thyroid conditions.

The following foods, however, are known to affect thyroid function:

Brassicas

Brassicas (e.g. cabbage, cauliflower, kale) may contribute to the formation of a goitre (swelling or enlargement of the thyroid gland) in some cases, but consumption would need to be very high before this is a real concern. In the UK, under normal dietary conditions, this is not normally a problem, and the risk is very low.

Kelp

Avoid products such as kelp, as they may interfere with thyroid function and wellbeing. Kelp supplement is derived from seaweed and is naturally high in iodine. Because of this, it is sometimes marketed as a ‘thyroid booster’ and can be purchased in dry preparations and tablets. As with iodine itself, it is of no health benefit to those with thyroid disease. 

Soya

Soya interferes with levothyroxine absorption, therefore if you are taking levothyroxine you should try to avoid soya. If you wish to take soya, you should leave as long as possible (at least four hours) between eating the soya and taking the levothyroxine.

Supplements

It is important to note that no vitamins and minerals (supplements) can provide the same nutritional  benefits as a healthy balanced diet. However, it is not always easy to maintain a varied and healthy diet. For this reason, you may wish to take supplements. If you decide to do this, you should avoid taking them in excessive amounts. Not only can this be harmful, some can also interfere with your thyroid function or your thyroid blood test results. So, you should let the person taking your thyroid function tests know if you have been taking supplements.

Please also note that supplements should never be taken as an alternative to prescribed medication.

We recommend you take appropriate advice from your doctor or pharmacist before taking any supplements or vitamins.

Biotin (vitamin B7)

This is used in many cosmetic products, as well as supplements, to promote hair and nail growth. Although its benefits are anecdotal, it is understandably popular among people living with hypothyroidism to address these issues but no clear evidence exists for a beneficial effect in hypothyroidism, even in people with additional autoimmune conditions. The daily recommended intake of biotin for an adult is 30mcg but many biotin supplements marketed for cosmetic reasons contain much higher doses, ranging from 5,000mcg to 10,000mcg. We recommend you be aware that these mega doses of biotin can sometimes result in incorrect TSH, FT4 and FT3 levels and may give a reading that suggests an overactive thyroid (hyperthyroidism). If you are taking biotin supplements the American Thyroid Association advises that you avoid taking them for two days before having thyroid blood tests to minimise the risk of a false reading.

Calcium

Some calcium-rich foods and supplements interfere with levothyroxine absorption. A gap of four hours between the two would be adequate to ensure there is no significant impact on blood thyroxine levels. If you use semi-skimmed or skimmed milk, this remains high in calcium despite being lower in fat.

Carnitine[iii]

Carnitine is found naturally in all tissues and body fluids. During the normal process of releasing energy from food, a type of activated oxygen is released which can damage our cells. Carnitine helps to reduce this effect. Our bodies make about one-quarter of the carnitine we need, the rest is provided by our diet and is found in red meat.  A trial of carnitine in people with hyperthyroidism found that it improved many of the symptoms, particularly irregular heartbeat. There is no evidence to suggest it benefits people with hypothyroidism.

Ginger

A study found that supplementing ginger in 2 x 500mg doses per day helped alleviate some symptoms of hypothyroidism. However, there were some limitations to the research suggesting that further human studies are needed with larger sample sizes, longer durations, different ginger doses, and a follow-up period after discontinuing the supplement. There is no requirement for food supplements to be licensed or registered with the UK government. However, all foods must comply with the relevant food law. So, if you want to try ginger supplementation be mindful that the products will most likely vary in contents and cost between brands. If you see no improvement in symptoms, then discontinue. [iv]

Iodine[v]

If you have a properly functioning thyroid, iodine is essential as it is required to produce thyroxine. It is particularly important in women who are pregnant as it is needed to ensure the development of a baby's brain during pregnancy and early life.

If you are taking levothyroxine for hypothyroidism (underactive thyroid) or for a goitre (thyroid swelling) there is no need to take iodine supplements.

If you are being treated for hyperthyroidism (overactive thyroid) taking an iodine supplement is unnecessary and can worsen the condition. The extra iodine can counteract the benefits of the anti-thyroid drugs.

BTF information about iodine

Iron

The thyroid needs iron to generate T4 and T3 (selenium, discussed below, is essential in converting  T4 into T3, which is the active form of thyroid hormone). A literature review found that iron deficiency is often associated with hypothyroidism, especially in pregnant women. Some iron tablets (ferrous sulphate) can interfere with the absorption of thyroxine therefore doctors recommend a four-hour interval between taking thyroxine and the iron. Follow the advice of your doctor or pharmacist and be aware that some multivitamin tablets contain iron.

Lemon balm or Melissa Officinalis

This is an antioxidant like carnitine and resveratrol and it is claimed it can improve sleep, skin quality and circulation. A study from the 1980s suggested lemon balm may be beneficial in Graves’ disease. The study showed that components of lemon balm could prevent the thyroid-stimulating antibodies that cause Graves’ disease from binding to the thyroid on/off switch.[vi]

A more recent report described two individual women whose overactive thyroids were improved by lemon balm. Their stimulating antibody levels decreased but this could have happened spontaneously as the disease followed its natural course. These laboratory experiments and case reports suggest that lemon balm may help Graves’ disease patients but controlled clinical trials are required before it can be recommended.

Magnesium

Magnesium can be found in legumes, nuts, seeds, and green leafy vegetables. Smaller amounts are found in meat and fish. It is reported to have several health benefits including improving bone health, mood, sleep quality and reducing anxiety. Some studies suggest that magnesium deficiency may be associated with hypothyroidism. Other studies show that increased magnesium levels can help with the control of Graves’ disease. However, the data is inconclusive at this stage.[vii]

Resveratrol

This acts similarly to carnitine, and has antidiabetic, anti-inflammatory and antioxidant effects. It is found in red wine. Unfortunately, there are no proper trials of its usefulness in relation to thyroid disease  [viii]

Selenium

This is found in Brazil nuts, tuna, sardines, eggs and legumes (e.g. beans, chickpeas, lentils). As mentioned above, it is vital in generating the more active T3 from T4. All of these foods are recommended as part of a healthy balanced diet.

The evidence around selenium’s benefits is mainly in patients with mild thyroid eye disease so it is recommended as a treatment for people with this condition. A large European [ix]study has shown that six months of selenium supplements had a beneficial effect on thyroid eye disease and were associated with improvement in the quality of life of participants. These positive effects persisted at 12 months. There were no side-effects.

Some trials show that selenium can bring thyroid antibody levels down in patients with Graves’ disease. However, there does not appear to be any link between taking selenium and improvement in thyroid function.[x] [xi]

BTF information about selenium and mild thyroid eye disease

Vitamin B12

Vitamin B12 helps the body to make red blood cells and keep the nervous system healthy. It also helps the body to release energy from food and use folate.

There is an association between vitamin B12 deficiency in patients with autoimmune thyroid disease secondary to pernicious anaemia. A recent meta-analysis found significantly lower levels of vitamin B12 in people with hypothyroidism (but not hyperthyroidism or sub-clinical hypothyroidism) than in healthy individuals. However, there is no substantial evidence to suggest thyroid function may improve by supplementing with B12.[xii] [xiii]

Vitamin D

Vitamin D helps regulate calcium and phosphate absorption and is needed for healthy bones, teeth and muscles.  A large number of studies[xiv] have investigated whether vitamin D is associated with thyroid disorders, with many, but not all, finding that low levels correlate with thyroid autoantibodies and maybe even features of thyroid cancer.

Since most people may be deficient in vitamin D (particularly in the autumn and winter months when the sunlight in the UK is not strong) the NHS advises that all adults and children over the age of five take a supplement of 10mcg each day. This applies during the autumn and winter for most people but you should consider taking this supplement throughout the year if you are concerned that you may not be getting enough sunlight even at other times of the year, e.g. you are not often outdoors or you tend to cover yourself up with clothes when you are outside.

If you have dark skin you are also at risk of not getting enough vitamin D from sunlight and should consider taking 10mcg supplements throughout the year.

BTF article on 'Vitamin D and thyroid disease’

Zinc

This is found in shellfish, beef, chicken and legumes and it is thought that it helps with thyroid function.[xv] A review of studies suggests that zinc [xvi], alone or combined with other supplements, may improve outcomes in people with hypothyroidism.  However, further large-scale trials are required to assess the role of zinc supplementation in those with thyroid problems and in the general population.

Always take the recommended dose

Although it is tempting to think that large doses of certain supplements will do us good, exceeding the recommended intake (RI) can often do us more harm than good. For example, a study has shown taking high-dose selenium supplements (more than 300 micrograms/day) increased all-cause rates of mortality. [xvii]

We therefore recommend you do not consume any vitamins or supplements in high doses, unless advised by your doctor. Please remember to check your thyroid medication patient leaflet to check whether the supplements are advised against. To avoid absorption issues, and unless otherwise indicated, you should always take supplements at least four hours apart from levothyroxine.

If you have any concerns about whether you should take vitamins or other supplements, please consult your doctor or pharmacist.

Further reading

British Dietetic Association – Supplements fact sheet

BTF information about iodine

BTF information about selenium and mild thyroid eye disease

BTF article on 'Vitamin D and thyroid disease'

References