Life Expectancy of Patients With Low-Normal Thyroid Function To the Editor Using the multistate life table method with data from the Rotterdam Study, Bano and colleagues,1 in a recent issue of JAMA Internal Medicine, showed that participants with low-normal thyroid function had longer life expectancy compared with those with high-normal thyroid function. Although we agree that the results of this study would contribute to reevaluating the reference range of thyroid hormones, Bano and colleagues1 need to provide more information about the association between thyroid hormone levels (within reference range) and mortality. Bano et al1 calculated life expectancy among tertiles of thyrotropin and free thyroxine considering the following 3 transitions: (1) incident cardiovascular disease (CVD), (2) mortality among those without CVD, and (3) mortality among those with CVD. It means that participants who already had a history of CVD at baseline and those who acquired CVD during the study period contributed to the number of “persons at risk” of mortality among those with CVD. However, it is not clear whether the effect of baseline thyroid hormone levels on mortality risk would last after the CVD event or would be homogenous among those who already had a history of CVD at baseline and those who acquired CVD during the study period. It is also unclear why person-years at risk are different between the 2 transitions: (1) incident CVD and (2) mortality among those without CVD. Providing the additional information, the comparison between the results of this study1 and those of previous studies would be more straightforward.2,3 It has been reported that subclinical hypothyroidism is associated with increased risk of CVD and mortality.4 Moreover, we previously reported that low-normal thyroid function had higher risks of cardiovascular and all-cause mortality than median-normal thyroid function.3 Physiologically, low thyroid function has been known to weaken cardiac function and increase systemic vascular resistance by regulating calcium uptake and inducing endothelial dysfunction, which can eventually cause CVD.5 Additionally, the association between low thyroid function and metabolic syndrome has been reported within the reference range.3 Therefore, Bano et al1 would need to explain how they interpreted the prolonged life expectancy of participants with low-normal thyroid function despite these physiological mechanisms.

中文翻译：

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甲状腺功能低下患者的预期寿命

Bano 及其同事在最近一期的 JAMA Internal Medicine 上使用多态生命表方法和鹿特丹研究的数据1 显示，甲状腺功能低下的患者的预期寿命给编辑器与甲状腺功能正常的人相比，预期寿命更长。尽管我们同意这项研究的结果将有助于重新评估甲状腺激素的参考范围，但 Bano 及其同事 1 需要提供更多关于甲状腺激素水平（在参考范围内）与死亡率之间关联的信息。Bano 等人 1 计算了促甲状腺素和游离甲状腺素三分位数的预期寿命，考虑以下 3 种转变：(1) 心血管疾病 (CVD)，(2) 无 CVD 患者的死亡率，(3) CVD 患者的死亡率。这意味着在基线时已经有 CVD 病史的参与者和在研究期间获得 CVD 的参与者对患有 CVD 的“处于死亡风险”的人数做出了贡献。然而，尚不清楚基线甲状腺激素水平对死亡风险的影响是否会在 CVD 事件后持续存在，或者在基线时已有 CVD 病史的人和在研究期间获得 CVD 的人之间是否相同。也不清楚为什么 2 次转变之间的风险人年不同：(1) CVD 事件和 (2) 没有 CVD 的人的死亡率。提供额外的信息，本研究的结果 1 与以往研究的结果之间的比较将更加直接。 2，