maandag 12 november 2012

Thyroid function and longevity: new insights into an old dilemma

Thyroid function changes in the elderly, and many studies in the last 30 yr have investigated the role of thyroid function in the aging process. Recent reports have convincingly shown that serum TSH levels increase with age, independent of the presence of antithyroid antibodies.

Thyroid Function and Longevity: New Insights into an Old Dilemma
Robin P. Peeters
Erasmus University Medical Center, Department of Internal Medicine, 3015 GE Rotterdam, The Netherlands

This suggests that thyroid function decreases with age. In contrast, other studies have shown low levels of serum TSH in the elderly. With regard to other thyroid function tests, most studies demonstrated an age-dependent decline in serum free T3 levels, whereas free T4 (FT4) levels remained relatively unchanged and rT3 levels increased with age.

The difficulty in interpreting these results is that the evaluation of thyroid function in the elderly is often complicated by the increased prevalence of chronic illness and the use of medication. Chronic illness is associated with low levels of T3 and high levels of rT3, and, depending on the duration and the severity of the illness, TSH and FT4 levels may be low as well. Some of these changes are similar to the changes in thyroid hormone levels observed in the elderly. Therefore, distinguishing between changes related to “normal” aging per se and changes that are abnormal, i.e. disease-related, is a major challenge. In addition, differences in iodine intake and in the presence of autoimmune thyroid disease between these study populations may play an important role as well.

There is evidence that a low activity of thyroid hormone might be beneficial in the elderly, whereas subclinical hyperthyroidism is a predictor of mortality. It has been demonstrated that subjects with exceptional longevity (centenarians; median age, 98 yr) have higher levels of TSH compared with controls.

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