Context: A relation between low thyroid activity and prolonged life span in humans has been observed. Several studies have demonstrated hereditary and genetic influences on thyroid function.
Objective: The objective of the study was to test whether low thyroid activity associated with extreme longevity constitutes a heritable phenotype, which could contribute to the familial longevity observed in the Leiden Longevity Study.
Design: This was a cross-sectional study.
Setting: The study was conducted at a university hospital in the city of Leiden, The Netherlands.
Participants: Eight hundred fifty-nine nonagenarian siblings (median age 92.9 yr) from 421 long-lived families participated in the study. Families were recruited from the entire Dutch population if at least two long-lived siblings were alive and fulfilled the age criterion of age of 89 yr or older for males and 91 yr or older for females. There were no selection criteria on health or demographic characteristics.
Intervention: Blood samples were taken for determination of serum parameters of thyroid function.
Main outcome measure: We calculated the family mortality history score of the parents of the nonagenarian siblings and related this to thyroid function parameters in the nonagenarian siblings.
Results: We found that a lower family mortality history score (less mortality) of the parents of nonagenarian siblings was associated with higher serum TSH levels (P = 0.005) and lower free T(4) levels (P = 0.002) as well as lower free T(3) levels (P = 0.034) in the nonagenarian siblings.
Conclusions: Our findings support the previous observation that low thyroid activity in humans constitutes a heritable phenotype that contributes to exceptional familial longevity observed in the Leiden Longevity Study.