Subclinical hyperthyroidism and hypothyroidism are both linked to higher mortality in the elderly, with the greatest mortality increases found in those with thyroid-stimulating hormone (TSH) values above 6.38 mIU/L, according to a retrospective cohort study.
Researchers analyzed medical records from 538 individuals with subclinical hyperthyroidism, 1,956 with subclinical hypothyroidism and 14,946 with normal thyroid-stimulating hormone levels, and found subclinical hyperthyroidism (TSH less than 0.35 mIU/L) was associated with an 80% greater risk of mortality over 10 years of follow-up, compared with normal TSH levels.
The study showed subclinical hypothyroidism (TSH greater than 4.2 mIU/L) was associated with a 68% greater mortality risk, even after adjustment for potential confounders such as age, sex, chronic kidney or lung disease, smoking, and hypertension.
The analysis also showed that when TSH values were stratified into quintiles for both subclinical hyperthyroidism and hypothyroidism, individuals with TSH levels above 6.38 mIU/L had the greatest excess of mortality, compared with other individuals with hypothyroidism, while there were no significant mortality differences between the quintiles in subclinical hyperthyroidism.
“Whether this should lead to less-restricted thyroid hormone replacement in elderly individuals with subclinical hypothyroidism is unclear, but these results certainly serve as preliminary evidence for the requirement for thyroid hormone replacement in the elderly with subclinical hypothyroidism, possibly with a higher thyroid-stimulating hormone threshold value,” wrote Dr. Alon Grossman from the Rabin Medical Center, Petah Tikva, Israel, and coauthors (Am J Med. 2016 Apr;129[4]:423-30).
No conflicts of interest were declared.