By Colin Michie, FRCPCH FRSPH FLS RNutr FRSA
“By these shores I was born: sound of the sea
came in at my window, life heaved and breathed in me then
with the strength of that turbulent soil.” - Kamau Braithwite From ‘South’
The magical functions of our millions of cells are controlled by hormones from one organ: the thyroid. These hormones contain iodine. Like the salt in our blood or the fatty acids in our brains, iodine links us to the turbulent soils of the sea.
Iodine is plentiful on Caribbean islands because most of earth’s supplies are oceanic. It is found in seaweeds, marine creatures or in soils that were once submerged. Iodine works as a biochemical driver or signaller in most living cells. All vertebrates have thyroids that drive brain development, hibernation, the moulting of fur and feathers. Iodine is trapped efficiently from our circulations by the thyroid. If you are a child in central Africa, India or Switzerland, the lack of iodine in local foods can cause your thyroid to expand, leading to a goitre, a mass in the neck.
Healthy thyroids weigh about 35g in adults. Their hormones are likely to spend a week or two moving through the body before being taken up into a cell, a steady process that starts when we are embryos. Like other hormones such as adrenaline, oestrogen or testosterone, they work inside cells. Thyroid hormones control the speed at which foods are converted into energy, our metabolic rate. They are crucial for the growth and reproduction of all cells, and particularly the development of our complex nervous systems.
Thyroid malfunctions are quite common. Most can be easily treated. If thyroid hormones are in short supply your weight increases, heart rate slows, you feel the cold. Dry skin, constipation and depression are common. This condition, myxoedema, can be fatal if not treated. Children with reduced thyroid function will not gain height and commonly have learning difficulties. Under-function or hypothyroidism is more common than the more dramatic over-function or thyrotoxicosis. Too much thyroxine causes a racing heartbeat, tremors and anxiety; there may be changes behind the eyes causing them to protrude. Whether a thyroid over or under-performs, its changes take place over weeks to months, making us less aware of its power.
Two centuries ago it was traditional practice in Switzerland to use seaweed recipes to treat children with a goitre. Iodine was first isolated by a French doctor, from seaweed. Having heard of this traditional therapy, he successfully treated young Swiss patients with goitres with an iodine preparation. This led to the supplementation of table salt with iodine to prevent goitre. Potassium iodide tablets may be given to protect the thyroid of those at risk of exposure to nuclear fallout dusts, as in 1986 Ukraine, in the region of Chernobyl. Such disasters release radioactive iodine that can poison thyroid cells or drive them to become malignant.
Most patients with underperforming thyroids need a daily dose of thyroid hormones rather than iodine. Over a century ago dried sheep thyroid injections treated myxoedema reasonably well. Today’s pharma-grade thyroid extracts are prepared from pigs. Over 5 million prescriptions of these are issued in the US each year to those who prefer safe but natural treatments. In 1949 synthetic thyroid hormone, levothyroxine, became available: this is now one of the top 5 prescribed drugs in the US. Just under 100 million scripts were recorded in 2020.
Thyroid activities are controlled by the pituitary gland that lies under the brain. This small gland runs like an air-conditioning control by releasing a driver: thyroid stimulating hormone. Your thyroid can be checked thoroughly by looking for symptoms, then measuring this thyroid stimulating hormone as well as thyroid hormones themselves. As it is wrapped around the voice-box, this organ can be rapidly scanned with ultrasound too. If it overperforms, a thyroid can be surgically removed, then a daily prescription of hormone provided for the patient.
Most of us will develop a lump or nodule in our thyroids, particularly as we age. The great majority of nodules do not need treatment but a very small proportion can become malignant. The thyroid is the most common site for malignancy in the endocrine system, and one of parts of the body often attacked by our own antibodies – autoimmune disease. Ultrasound can be used to check the thyroid and it may be biopsied too, under local anaesthetic, using a fine needle. A blood test or liquid biopsy is provided in some centres. Thyroid cells in these can be characterised so as to direct treatments.
Our busy, bossy little thyroid glands rarely attract daily attention, although they are in full view. Their steady performance, using a peculiarly ancient signalling system, keeps our metabolic fires burning, connecting our hearts, heads, health and warmth to those tides of life.