Thyroid hormone levels are linked with well-being among patients on thyroid hormone replacement therapy, a recent study has found.
The thyroid gland, in the lower neck, produces hormones which regulate our metabolism and have direct effects on most organs. All cells in the human body will respond to changes in thyroid hormones with a change in the rate at which they work.
A lack of thyroid hormone, hypothyroidism, has long been linked to cognitive and memory problems and mood disorders, possibly through the brain chemical serotonin. But could normal hormone levels also be linked to well-being?
So far, the evidence for smaller variations in thyroid hormone levels affecting mood and psychological wellbeing remains controversial. Some studies have suggested a link with depression, mental impairment and memory loss, but others have failed to find such a link. However, in studies where thyroid hormone levels are raised using hormone therapy, psychological well-being tends to improve.
A team of researchers from the Henry Wellcome Lab for Integrative Neuroscience and Endocrinology at Bristol University, UK set out to investigate changes in thyroid hormone levels within the “normal” range.
Dr. Colin Dayan and his team recruited 697 men and women with hypothyroidism about to take part in a study on the treatment. All were 18 to 75 years old (mean 57 years) and were taking at least 100ug of thyroxine as thyroid hormone replacement therapy. Most patients (68 percent) currently had thyroid hormone levels within the normal range.
Measurements were taken of their levels of the hormone free thyroxine (fT4), and well-being was assessed using the reliable and widely-used General Hospital Questionnaire. The participants also filled in the Hospital Anxiety and Depression Scale and the Thyroid Symptom Questionnaire.
Overall, those with higher levels of fT4 had significantly better well-being. This link could not be explained by age or gender. A significant link also was found between lower well-being and higher levels of TSH, thyroid-stimulating hormone. This was expected, as higher TSH can indicate thyroid problems.
Those with higher fT4 also had less severe symptoms on the Thyroid Symptom Questionnaire, but no links were found with the Hospital Anxiety and Depression Scale. The same relationships were found when those outside normal levels were excluded from the analysis.
Dr. Dayan and colleagues said: “Interestingly, no clear association was seen with the Anxiety and Depression Scale, which may suggest that the thyroid function influences parameters of psychological well-being not typical of anxiety or depression.” They explain that the well-being questionnaire refers “more generally to psychological well-being comparing current status to how patients would ‘usually’ expect to feel.”
They concluded that differences in fT4 and TSH concentration may determine psychological well-being in hypothyroid patients on medication. Because of this, they recommend that fT4 levels and TSH levels should be taken into account when adjusting hormone therapy dosages, as TSH alone may not be a perfect indicator of well-being.
They suggest that variation in thyroid hormone levels, even in people without thyroid dysfunction, may affect psychological well-being, and call for large population-based studies to explore this possibility.
Further evidence for this theory comes from a 2005 study which actually found positive effects on self-rated mental and physical health among participants with undiagnosed hyperthyroidism, that is, higher than normal thyroid hormone levels.
Rather than studying thyroid patients, the researchers tested people in the general population. They investigated links between undiagnosed thyroid disorders and symptoms of mental ill health among 3,941 adults in Pomerania, Germany.
Unexpectedly, those with undiagnosed hypothyroidism were no different from the “normal” group, but hyperthyroidism was associated with positive overall effects on self-rated mental and physical health. Nevertheless, hyperthyroidism is dangerous and must be treated.
For many years, thyroid hormones, together with standard medications, have been used to treat depression and both the manic and depressed phases of bipolar disorder. However, the role of these hormones in triggering mood disorders needs further study.
According to Dr. Dayan, around five to 10 percent of adults have abnormal thyroid hormone levels, but it’s usually only very slightly abnormal and studies show that they would gain no benefit from taking thyroxine. Only one in 100 hypothyroid adults need treatment.
Saravanan, P., Visser, T. and Dayan, C. M. Psychological wellbeing correlates with free T4 but not free T3 levels in patients on thyroid hormone replacement. Journal of Clinical Endocrinology & Metabolism, Vol. 91, September 2006, pp. 3389-93.
Grabe, H. J. et al. Mental and physical complaints in thyroid disorders in the general population. Acta Psychiatrica Scandinavica, Vol. 112, October 2005, pp. 286-93.