How Does Thyroid Function Affect Aging, Metabolism, and Longevity?

The short answer

Thyroid hormones regulate metabolic rate, cardiovascular function, bone turnover, and cognitive function. Hypothyroidism (underactive thyroid) is associated with elevated LDL cholesterol, weight gain, fatigue, and cognitive slowing. Hyperthyroidism (overactive thyroid) causes atrial fibrillation, bone loss, and cardiovascular stress. Subclinical hypothyroidism — elevated TSH with normal thyroid hormones — affects 10–15% of adults over 65 and is associated with cardiovascular risk.

What the evidence actually shows

A 2010 meta-analysis by Rodondi et al. in JAMA, pooling 11 prospective cohorts and 55,287 participants, found that subclinical hypothyroidism was associated with a 20% increased risk of coronary heart disease and a 19% increased risk of cardiovascular mortality, with the risk most pronounced in those with TSH ≥10 mIU/L. Cappola et al. (2006) in JAMA found that subclinical hyperthyroidism (suppressed TSH with normal thyroid hormones) was associated with a 3-fold increased risk of atrial fibrillation in older adults. MedlinePlus notes that thyroid diseases affect the body's metabolism and can cause a wide range of symptoms, and that thyroid function testing is recommended for older adults with unexplained symptoms.

"Subclinical hypothyroidism was associated with a 20% increased risk of coronary heart disease and cardiovascular mortality."

— Rodondi et al., JAMA 2010

What the major health authorities say

MedlinePlus recommends thyroid function testing (TSH measurement) for individuals with symptoms of thyroid dysfunction. The American Thyroid Association recommends screening for thyroid dysfunction in all adults over 35, with repeat testing every 5 years. The NIA notes that thyroid diseases are more common in older adults and that symptoms can be subtle or atypical, making testing particularly important in this age group.

Practical implications

A simple TSH blood test is the most sensitive screening test for thyroid dysfunction and should be part of routine health monitoring, particularly for adults over 50 with unexplained fatigue, weight changes, cognitive symptoms, or cardiovascular risk factors. Hypothyroidism is treated with levothyroxine (synthetic T4), which is highly effective. Iodine is essential for thyroid hormone production — most people in developed countries get adequate iodine from iodised salt and dairy, but those on very restricted diets may be at risk of deficiency.

Where reasonable people still disagree

• Whether subclinical hypothyroidism (TSH 4.5–10 mIU/L) in older adults should be treated with levothyroxine, given mixed evidence from RCTs.
• The optimal TSH target range for older adults, which may be higher than for younger adults given age-related changes in thyroid physiology.
• Whether T3 supplementation (liothyronine) provides additional benefit over T4 alone for patients with persistent symptoms on levothyroxine.