Читать книгу The Healthy Thyroid: What you can do to prevent and alleviate thyroid imbalance - Patsy Westcott - Страница 46

To understand these links, it is necessary to look more closely at the chemistry of the brain and some of the discoveries that have been made concerning how the brain and body ‘talk’ to each other. Depression has been found to be linked to changes in both the hypothalamus-pituitary-thyroid axis and the hypo – thalmus – pituitary – adrenal axis – two key hormonal circuits that link the brain and the body.

A major step towards understanding depression came with the discovery that the condition is linked to a shortage of the brain chemical serotonin, sometimes called the ‘happiness hormone’. This led to the development of a new class of antidepressants called selective serotonin reuptake inhibitors (SSRIs) which, as the name suggests, selectively block serotonin receptors to cause levels of serotonin – and feelings of wellbeing – to rise. These drugs, of which Prozac is the most well known, are now considered the standard treatment for depression.

Recently, researchers found that people who are depressed tend to have raised levels of thyroxine (T₄). At the same time, they have disturbances in their body clock causing lower daytime levels and a lower-than-normal night-time surge of thyroid-stimulating hormone, thought to be due to lack of serotonin. This is yet another example of how the brain and body communicate. Some doctors also suggest that the activity of T₃ is also reduced, although this is not as yet supported by any clear evidence.

A number of psychiatrists, particularly in the US, have found that a T₃ plus antidepressant ‘cocktail’ helps lift depression faster in the 30–40 per cent of people who seem to be resistant to antidepressants. Interestingly, adding the more usual thyroid treatment, T₄, has not proved effective, which suggests that the ability to convert T₄ to T₃ in the brain may be damaged in depressed people. Although most studies were carried out with the older tricyclic antidepressants that are not as widely used these days, it is thought that adding a dash of T₃ to an SSRI might be equally effective.