The effect hypothyroidism has on aging is complex, but some evidence suggests it may be associated with prolonged life.

Hypothyroidism, also called underactive thyroid, occurs when your thyroid gland isn’t making enough hormones to support bodily functions. Too-low levels of thyroid hormones cause many of the processes in your body to slow down.

A body “slow down” doesn’t necessarily mean hypothyroidism slows aging. Aging is a complex process that involves much more than how quickly your cells initiate their functions.

Living with hypothyroidism can slow processes in your body that contribute to aging, such as your metabolism, but its exact effects on the aging process are unclear.

Metabolism is a broad term for your body’s use of energy. It involves functions related to converting food into energy and those involving energy uses at the cellular level. Your metabolic rate is the speed at which these processes occur.

Slowed metabolism from hypothyroidism can affect cell aging in a variety of ways, including the rate at which cells turnover, or how quickly your body replaces old cells with new ones.

Longer-lived cells conserving energy may sound like the fountain of youth, but aging isn’t so simple, and how significantly metabolism affects overall biological age isn’t known.

Biological aging is defined as a progressive, gradual decline in function across all systems in your body over time. While it includes changes to your metabolism, biological aging is a complex process involving many other factors, such as:

  • DNA damage
  • changes in genetic expression
  • structural dysfunction within cells
  • hormonal changes
  • decreased activity of immune function
  • stem cell exhaustion

Hypothyroidism can affect the function of almost every organ in your body.

If left untreated or in severe presentations such as myxedema, health challenges that affect life expectancy, such as heart failure, are possible.

With treatment, most people living with hypothyroidism see no significant decline in life expectancy, and problematic symptoms typically resolve in weeks to months.

Can hypothyroidism extend your life expectancy?

Even though the effects of hypothyroidism on the aging process aren’t well understood, hypothyroidism may promote a longer life overall, according to a study from 2015.

Subclinical hypothyroidism, when thyroid hormone levels are low but free thyroid hormone levels are in the expected range, may positively affect factors linked to longevity such as genetic expression and hormone function.

Additionally, in a 2017 study of more than 7,000 participants, people with low-normal thyroid function lived up to 3.5 years longer overall and 3.1 years longer without cardiovascular disease, compared with people with high-normal thyroid function.

It may not be that hypothyroidism, specifically, is the cause of a longer life span. It may be that lower thyroid function is part of a heritable phenotype, a passed-down set of traits, that promote longer life.

An older study from 2010 found a family history of long life in parents was associated with lower thyroid hormone production and longer life spans in children, compared with the general population.

The biological aging process naturally causes a decline in organ function. Your thyroid isn’t exempt, which is one of the reasons why hypothyroidism is more common in people over 60 years of age.

Despite the increased prevalence, hypothyroidism symptoms in older adults are often less severe compared with those in young people.

This may be partially due to how natural age-related experiences can mimic the symptoms of hypothyroidism, making them less noticeable.

As you get older, for example, you may naturally experience cold intolerance, but cold intolerance can also be a symptom of hypothyroidism. Symptoms of other chronic illnesses commonly seen later in life can also conceal symptoms.

Another reason why you might have milder symptoms of hypothyroidism as an older adult is because your hormone needs have changed with time.

According to a 2019 literature review, people require fewer thyroid hormones as they age to achieve proper organ function. In many cases, lower levels of thyroid hormones in older adults don’t cause major deficits in function and may not even need levothyroxine therapy, the gold standard of medication used in treatment.

Levothyroxine is a synthetic form of the thyroid hormone thyroxine. It’s one of the most widely used medications in the treatment of hypothyroidism and works by supplementing thyroid hormone when your natural levels are too low.

Although regularly prescribed for thyroid management, growing controversy surrounds the long-term use of levothyroxine.

Not only may it be overprescribed in older adults, but it may also increase your risk of developing cancer, heart disease, and osteoporosis — all factors that can negatively affect your quality of life with hypothyroidism.

There’s currently no evidence that taking levothyroxine to treat hypothyroidism will accelerate your aging or lower your life expectancy.

Important processes in your body, such as your metabolism, slow down when your thyroid gland doesn’t produce enough hormones. But delayed cellular functions don’t mean hypothyroidism slows aging.

Many collective factors cause biological aging, the natural decline of body functions over time. Damage to your DNA, changes in your immune system, and cellular dysfunction all matter.

While it’s unclear exactly how hypothyroidism factors into the aging process, having an underactive thyroid may be part of a set of characteristics that promote increased longevity.