During the month of January, which is National Thyroid Awareness Month, it is important to know that this small gland can have an outsized impact on day-to-day function—especially in older adults. The thyroid helps regulate metabolism, heart rhythm, temperature, mood, and energy. When thyroid hormone levels run too low (hypothyroidism) or too high (hyperthyroidism), changes can show up as memory problems, confusion, anxiety, apathy, sleep disruption, and the overall feeling that “something is off.”
For dementia caregivers, thyroid dysfunction matters for two reasons:
- It can look like dementia or make dementia symptoms worse.
- Some forms—especially “overactive” thyroid—appear linked to a higher long-term risk of cognitive decline and dementia.
The key connection: thyroid hormone levels influence the brain (and the heart)
What Research Shows
Across several large studies and meta-analyses:
- Hyperthyroidism (overactive thyroid) and subclinical hyperthyroidism (thyroid levels are “borderline,” sometimes without obvious symptoms) are repeatedly associated with higher dementia risk.
- “High-normal” thyroid function (still technically in the lab reference range, but toward the higher end) has also been associated with increased dementia risk in at least one well-known prospective study.
- For hypothyroidism (underactive thyroid) and subclinical hypothyroidism, findings are mixed—some studies show little or no increased risk overall and results vary by age, severity, and how studies define thyroid disease.
Bottom line: Overactive thyroid patterns show the most consistent signal for elevated dementia risk, while underactive thyroid is more complicated and may be more about symptom overlap and quality of life than clear-cut dementia causation.
The science behind the thyroid–dementia link
Researchers think several pathways may connect thyroid dysfunction to brain health:
1. Brain energy and chemistry effects
Thyroid hormones help regulate how brain cells use energy, how neurons communicate, and how the brain maintains healthy connections. When levels are too high or too low, it can affect attention, processing speed, mood, and memory, which is sometimes in ways that resemble dementia (or intensify existing dementia symptoms).
2. Vascular (blood flow) pathways—especially with hyperthyroidism
Overactive thyroid increases the risk of atrial fibrillation (AFib), which is an irregular heart rhythm that can raise stroke risk and is also associated with cognitive decline and dementia (including from “silent” micro-injuries).
This is one reason clinicians pay close attention to thyroid levels in older adults: protecting the heart can help protect the brain.
3. Possible links to Alzheimer’s-related biology
Some reviews summarize emerging evidence that thyroid dysregulation may interact with Alzheimer’s-related processes (like amyloid/tau pathways), inflammation, and oxidative stress.
Symptoms caregivers should watch for (hypo vs. hyper)
Because symptoms can be subtle, or get attributed to “aging” or “dementia progression,” thyroid issues are easy to miss.
Underactive thyroid (hypothyroidism) may look like:
- Fatigue, low motivation, increased sleep
- Depression, slowed thinking, “brain fog”
- Feeling cold, constipation
- Weight gain (not always), dry skin, hair thinning
- Slower heart rate
- New or worsening memory/attention issues
Overactive thyroid (hyperthyroidism) may look like:
- Anxiety, agitation, irritability, restlessness
- Trouble sleeping
- Heat intolerance, sweating
- Unexplained weight loss (or increased appetite)
- Tremor, muscle weakness
- Fast or irregular heartbeat / palpitations (possible AFib)
- More frequent bowel movements
Red flags that deserve quicker follow-up
- Sudden change in confusion, behavior, sleep, or appetite
- New heart racing, palpitations, dizziness, shortness of breath
- Unexplained weight change plus mood/cognitive change
- A person with dementia who suddenly seems to “drop” in function without a clear reason
Many of these can be thyroid-related, medication-related, infection-related, dehydration, or other treatable triggers; therefore, it is worth checking.
How to reduce risk (and protect day-to-day function)
While you cannot address thyroid disfunction with over the counter medications or home remedies, you can reduce risk by catching problems early and avoiding extremes.
1. Ask about thyroid testing when symptoms shift
A simple blood test (often TSH with free T4) can identify many thyroid issues. This is especially relevant for:
- Older adults
- People with new cognitive or mood changes
- Anyone with unexplained weight change or heart rhythm symptoms
- People taking thyroid replacement (to avoid over- or under-treatment)
2. Make medication review a routine habit
Bring a current medications list to doctor visits and ask:
- “Could any medications be affecting thyroid levels or symptoms?”
- “If my loved one takes thyroid hormone, are levels being monitored to avoid overtreatment?” Over-replacement (too much thyroid hormone) is a common concern in older adults and can raise heart risks that may indirectly affect brain health.
3. Protect the heart to protect the brain (especially with hyperthyroidism)
Because hyperthyroidism is strongly linked with AFib risk, monitoring and treating rhythm issues, as well as managing blood pressure, diabetes, sleep, and stroke risk, are important.
4. Treat the “treatable” (even if dementia is present)
Even when someone already has dementia, addressing thyroid dysfunction may improve:
- Energy and participation
- Sleep
- Mood/anxiety
- Attention and day-to-day steadiness
It may not reverse dementia, but it can reduce avoidable suffering and “extra” confusion.
A caregiver-friendly script for the next appointment
If you have noticed changes in your loved one with dementia as described above, you may wish to address the issue at the next doctor appointment. Here are some suggested talking points:
“We have seen changes in energy/mood/sleep/heart rate and cognition. Could thyroid dysfunction be contributing? Would it make sense to check TSH and free T4 and review medications to ensure we are not over- or under-treating the present thyroid disfunction?”
The bottom line for caregivers
Research supports a meaningful thyroid–brain connection, but it is not as simple as “thyroid disease causes dementia.” The strongest evidence is around overactive thyroid patterns and dementia risk, while hypothyroidism findings are mixed and often overlap with depression, medication effects, and other common aging-related issues.
