This piece was written by our resident dietitian – Maeve Hanan.
What is the Thyroid?
This small butterfly-shaped gland that is located in the front of the neck secretes important hormones, thyroxine (T4) and triiodothyronine (T3), which help regulate the body’s metabolism. Thyroid hormones are released when the thyroid gland is stimulated by thyroid stimulating hormone (TSH). This is a hormone released by another gland in the brain called the pituitary.
What is Thyroid Disease?
Different types of thyroid disorders affect either its structure or function. The two main types types of thyroid diseases are:
- Hypothyroidism (underactive thyroid): This is the most common type of thyroid disease, and occurs when the thyroid is not producing enough thyroxine. Signs and symptoms include: tiredness, low mood, dry skin, thinning hair, sensitivity to the cold, constipation, low libido, menstrual disturbance, weight gain, low mood and difficulty concentrating .
- Hyperthyroidism (overactive thyroid): This occurs when the thyroid produces too much thyroxine. Signs and symptoms include: weight loss, altered appetite (increased or decreased), irritability, sweating, tremor, anxiety, heat intolerance, diarrhoea, loss of libido, menstrual disturbance, and a goitre (enlarged thyroid gland).
If you notice any lumps or swelling of your neck it is important to speak to your GP.
Nutrition for Thyroid Health
This mineral is needed to produce thyroid hormones. Therefore, iodine is vital for healthy thyroid function, and particularly important for those with hypothyroidism to prioritise. The UK recommended daily intake of iodine for adults is 150mcg per day, which increased to 200 mcg per day for breastfeeding and pregnant women (1).
The main source of iodine in the UK diet is in cow’s milk and yogurt. Iodine is also found in:
- certain fortified plant-based drinks (1)
Therefore those following a vegan diet need to pay particular attention to their iodine intake, and some may benefit from taking an iodine supplement.
If enough iodine can’t be consumed in the diet, it is recommended to speak with your doctor before starting any iodine supplements, and opting for “potassium iodide” or “potassium iodate” supplements that contain no more than 150 mcg per daily dose (1). Those with thyroid disease should check with their GP before taking additional iodine. As per advice from the British Thyroid Foundation, if you are being treated for hyperthyroidism (overactive thyroid), taking an iodine supplement is unnecessary and can worsen the condition. Also, if you have hypothyroidism that isn’t caused by iodine deficiency, then taking iodine supplements is not recommended (2).
This mineral plays a role in thyroid health, including forming part of the defence system for the thyroid and thyroid hormone metabolism (3).
Brazil nuts are a particularly good source of selenium, infact just one Brazil nut can provide an adult’s daily selenium requirement (4). Selenium is also found in:
- cashew nuts
- white pasta
- brown bread (5)
Selenium supplements should be approached with caution, as consuming too much of this mineral may be harmful for overall health (3).
Zinc has been found to regulate both the creation and function of thyroid hormones (6).
Dietary sources of zinc include:
- dark chicken meat
- cashew nuts
- pumpkin seeds (7)
There is a link between iron deficiency and hypothyroidism, and this mineral is needed for thyroid metabolism (8).
Dietary sources of iron include:
- red meat
- fortified cereals
- tofu (9)
However, it is important to be aware that iron supplements can interfere with thyroid medication like Levothyroxine. Therefore a 4-hour gap is often advised between taking Levothyroxine and iron supplements (9). Similarly, a 4-hour gap is recommended between taking Levothyroxine and calcium-rich foods and supplements (10).
It is thought that people with autoimmune-related thyroid disease, such as Hashimotos or Grave’s disease, have a higher risk of low vitamin B12 levels (11).
This vitamin is important for obtaining energy from food, making red blood cells and mental health including healthy nerve function, creating brain chemicals and signalling molecules (12).
Dietary sources of vitamin B12 include:
- muscle meat
- fortified cereals
- nutritional yeast (12)
There is an association between vitamin D deficiency and Hashimoto’s disease (an autoimmune condition that causes hypothyroidism) ; and vitamin D deficiency is a very common issue across the UK, regardless of thyroid health (13, 14).
Vitamin D can be found in:
- oily fish
- egg yolks
- certain fortified drinks and breakfast cereals
- mushrooms which have been exposed to UV light (15)
However, it is difficult to obtain our full vitamin D requirements from food alone, as the best source of vitamin D is sunlight or vitamin D supplements. Therefore the UK government recommends a 10μg of vitamin D per day from October to March (16).
What About Goitrogens?
Goitrogens are compounds found in food which may interfere with thyroid function. These can be found in:
- sweet potato
- bok choi
- soya-based foods
However, cooking these foods can reduce goitrogen levels and consuming goitrogens is often only an issue when they are eaten in very high amounts or when an iodine deficiency is present (17).
Although soya is a goitrogen that can interfere with the absorption of Levothyroxine , the British Dietetic Association state that “thyroxine medication is always advised to be taken on an empty stomach and soya should not be excluded by those with an underactive thyroid gland as their medication dose can easily be modified” (18).
Take Home Message
There are a number of nutrients which play an important role in thyroid health. A balanced diet is the best way of consuming the nutrients that are needed to support thyroid health; with the exception of vitamin D which is more likely to be needed in supplement form. Please seek support from a Registered Dietitian for individualised support with diet and thyroid disease.
More information on living with thyroid disease can be found here.
All information provided by The Food Medic is provided for general information purposes only, and should not be treated as a substitute for advice given by your GP or any other healthcare professional.
(1) BDA (2019) “Iodine Food Fact Sheet” [accessed April 2021 via: https://www.bda.uk.com/resource/iodine.html]
(2) British Thyroid Foundation (BTF) “Iodine and thyroid” [accessed April 2021 via: https://www.btf-thyroid.org/iodine-and-thyroid]
(3) Rayman (2012) “Selenium and human health”. The Lancet, 379: 1256-1268 [accessed April 2021 via: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)61452-9]
(4) USDA FoodData Central [accessed April 2021 via: https://fdc.nal.usda.gov/fdc-app.html#/food-details/1100514/nutrients]
(5) NIH (2021) “Selenium Fact Sheet for Health Professionals” [accessed April 2021 via: https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/]
(6) Severo et al. (2019) “The Role of Zinc in Thyroid Hormones Metabolism”. Int J Vitam Nutr Res; 89(1-2):80-88 [accessed April 2021 via: https://pubmed.ncbi.nlm.nih.gov/30982439/]
(7) NIH (2021) “Zinc Fact Sheet for Health Professionals” [accessed April 2021 via: https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/]
(8) Ashraf et al. (2017) “Chronic anemia and thyroid function” Acta Biomed, 88(1): 119–127 [accessed April 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6166193/]
(9) NIH (2021) “Iron Fact Sheet for Health Professionals” [accessed April 2021 via: https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/]
(10) British Thyroid Foundation (BTF) “Thyroid and diet factsheet” [accessed April 2021 via: https://www.btf-thyroid.org/thyroid-and-diet-factsheet]
(11) Osborne & Sobczyńska-Malefora (2015) “Autoimmune mechanisms in pernicious anaemia & thyroid disease”. Autoimmun Rev: 14(9) [accessed April 2021 via: https://pubmed.ncbi.nlm.nih.gov/25936607/]
(12) NIH (2021) “Vitamin B12 Fact Sheet for Health Professionals” [accessed April 2021 via: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/]
(13) Ucan et al. (2017) “Vitamin D Treatment in Patients with Hashimoto’s Thyroiditis may Decrease the Development of Hypothyroidism”. Int J Vitam Nutr Res; 86(1-2):9-17 [accessed April 2021 via: https://pubmed.ncbi.nlm.nih.gov/28697689]
(14) SACN (2016) “Vitamin D & Health” [accessed April 2021 via: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/537616/SACN_Vitamin_D_and_Health_report.pdf]
(15) BDA (2019) “Vitamin D: Food Fact Sheet” [accessed April 2021 via: https://www.bda.uk.com/resource/vitamin-d.html]
(16) NHS Website (2020) “Vitamin D” [accessed April 2021 via: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/]
(17) Rungapamestry et al. (2007) “Effect of cooking brassica vegetables on the subsequent hydrolysis and metabolic fate of glucosinolates”. Proc Nutr Soc, 66(1):69-8 [accessed April 2021 via: https://pubmed.ncbi.nlm.nih.gov/17343774]
(18) BDA (2017) “Soya Foods: Food Fact Sheet” [accessed April 2021 via: https://www.bda.uk.com/resource/soya-foods.html]