Thyroid stimulating hormone (TSH) is produced by the pituitary gland in the brain, and acts on the thyroid gland to control thyroid function, which in turn controls metabolism. TSH levels are opposite thyroid hormone levels. When thyroid hormone levels are low and the gland is underactive, TSH levels are high. When the thyroid is overactive and thyroid hormone levels are high, TSH levels are low. While there may be minor changes in TSH levels during the course of the day, in general, both TSH and thyroid hormone levels are stable over time. However, in some individuals, TSH levels are more variable and it is known that TSH levels are generally higher in older adults than in younger people. This study aimed to determine changing thyroid function (variability) with aging and examine the association of these changes with survival, by analyzing thyroid function over time. The authors included participants from the Baltimore Longitudinal Study of Aging (BLSA), which is a long-term study of aging with continuous enrollment of healthy volunteers living independently in the community.
THE FULL ARTICLE TITLE:
Mammen JS et al. Unstable thyroid function in older adults is caused by alterations in both thyroid and pituitary physiology and associated with increased mortality. Thyroid, 2017 Nov;27(11):1370-1377.
SUMMARY OF THE STUDY
The study included 1294 participants in the BLSA who had normal thyroid function tests and were not on any thyroid hormone medications or other medications known to interfere with thyroid function. Of these participants, 464 were younger than 60 years old at the start of the study, 291 were aged 60-69, 327 were aged 70-79 and 206 were over 79 years old. The study focused on a subgroup of 640 participants who had at least three tests of TSH and free T4 over seven years.