Restoring Energy as You Age: Common, Checkable Causes of Fatigue

Feeling more tired than you used to is one of the most common complaints heard in primary and metabolic care, and it is also one of the most frequently dismissed as simply "getting older." Age does bring real physiological changes, but persistent, significant fatigue is not something you have to accept without investigation. Many causes of fatigue are identifiable with straightforward lab work and a thorough history, and many are treatable.

At Best Version of You, we see patients in Stroudsburg, PA and throughout the Poconos, as well as by telehealth in PA, NJ, NY, and DE, who assumed their exhaustion was inevitable and were surprised to find a specific, addressable cause. This article walks through the most common contributors and what a reasonable evaluation looks like.

Sleep: The First Thing to Rule Out

Before looking at labs, it is worth honestly assessing sleep quality and quantity. Many adults quietly accumulate sleep debt over years, and sleep architecture changes with age — lighter, more fragmented sleep becomes more common. Sleep apnea, which becomes more prevalent with age and weight gain, is frequently undiagnosed and causes daytime fatigue even when the person does not remember waking during the night. Snoring, witnessed pauses in breathing, morning headaches, and waking unrefreshed are clues worth mentioning to a provider.

Other sleep disruptors common with age include frequent nighttime urination, restless legs, chronic pain, and anxiety. Addressing sleep is often the single highest-yield intervention for fatigue, but it is frequently overlooked in favor of jumping straight to supplements or stimulant-like fixes.

Thyroid Function

An underactive thyroid (hypothyroidism) is a classic and very treatable cause of fatigue, along with weight gain, cold intolerance, constipation, and dry skin. Thyroid problems become more common with age, particularly in women, and can develop gradually enough that symptoms are mistaken for normal aging. A standard thyroid-stimulating hormone (TSH) test, sometimes along with free T4, is usually the starting point. Milder, subclinical thyroid dysfunction can also contribute to fatigue and is worth discussing — see our article on subclinical hypothyroidism and weight loss for more detail.

Iron, B12, and Vitamin D

Iron deficiency, with or without anemia, is a common and often overlooked cause of fatigue, particularly in women with heavy menstrual periods, people with certain dietary patterns, and anyone with unexplained blood loss. Ferritin, a marker of iron stores, can be low even when a standard blood count still looks acceptable, so a more complete iron panel is sometimes needed to catch it.

Vitamin B12 deficiency becomes more common with age, partly because stomach acid production can decline over time, affecting B12 absorption, and partly due to certain medications, including long-term use of some acid-reducing drugs and metformin. Untreated B12 deficiency can cause fatigue, neurological symptoms, and, if prolonged, irreversible nerve damage, which is why it is worth checking rather than guessing. Vitamin D deficiency is also widespread, particularly in northern climates like the Poconos during winter months, and has been associated with fatigue, mood changes, and musculoskeletal aches, although the research on supplementation reversing fatigue specifically is mixed.

Hormonal Changes

For women, perimenopause and menopause bring hormonal shifts that commonly include fatigue, sleep disruption, mood changes, and brain fog, often well before periods stop entirely. These changes are frequently misattributed to stress or aging alone. If hormonal shifts seem to be playing a role, our page on hormone therapy for women outlines evaluation and treatment options.

For men, testosterone levels decline gradually with age for many, and low testosterone can present as fatigue, reduced motivation, decreased muscle mass, and low libido. This is not universal and should be confirmed with appropriate morning testosterone testing rather than assumed from symptoms alone; our testosterone therapy for men page covers how that evaluation works.

Blood Sugar and Metabolic Factors

Both high and low blood sugar patterns can cause fatigue, and insulin resistance in particular can produce an energy pattern where people feel fine after a low-carbohydrate meal but sluggish and foggy an hour or two after a high-carbohydrate one. As discussed in our article on insulin resistance with a normal A1C, this pattern can exist well before standard diabetes screening catches it. If you are also carrying extra weight or have a family history of diabetes, broader metabolic lab testing can help clarify whether blood sugar regulation is contributing to your fatigue.

Mood and Mental Health

Depression and anxiety are common and underdiagnosed causes of persistent fatigue, and they frequently coexist with the physical causes described above rather than existing separately from them. Fatigue from depression can feel physical rather than emotional — heavy limbs, difficulty concentrating, low motivation — which is part of why it is sometimes missed. A thorough evaluation should include questions about mood, stress, and major life changes, not only lab values.

Medications and Chronic Conditions

As people take more medications with age, the cumulative sedating or fatigue-promoting effects of several drugs together can add up even when each one seems reasonable individually. Blood pressure medications, antihistamines, muscle relaxants, certain antidepressants, and some pain medications can all contribute to daytime tiredness. A periodic medication review, especially after a new prescription is added, is a simple step that is sometimes overlooked when fatigue is being investigated.

Chronic conditions such as heart disease, kidney disease, chronic lung conditions, and autoimmune disorders can also present with fatigue as an early or prominent symptom, sometimes before other signs become obvious. This is one more reason a thorough history and basic labs, rather than jumping directly to supplements, is the more reliable starting point when fatigue has lasted more than a few weeks.

What a Reasonable Fatigue Workup Looks Like

A sensible starting evaluation for persistent fatigue in adults typically includes a complete blood count, a comprehensive metabolic panel, thyroid testing (TSH, sometimes free T4), vitamin B12, ferritin or a full iron panel, vitamin D, and, depending on age, sex, and symptoms, sex hormone levels such as testosterone or estrogen. A fasting glucose or A1C, and sometimes fasting insulin, can screen for blood sugar issues. Not every patient needs every test, and the right panel depends on your history, symptoms, and exam findings, which is why a conversation with a provider matters more than ordering every test available.

When to See a Provider

Fatigue that persists for more than a few weeks, interferes with daily function, or comes with other symptoms such as unexplained weight change, mood changes, hair loss, cold or heat intolerance, heavy or irregular periods, shortness of breath, or chest discomfort deserves a medical evaluation rather than self-treatment with caffeine or supplements. Sudden, severe fatigue, especially with chest pain, trouble breathing, or confusion, needs urgent medical attention.

Simone Blount, FNP-BC, evaluates fatigue and related metabolic and hormonal causes in person in Stroudsburg, PA and by telehealth throughout Pennsylvania, New Jersey, New York, and Delaware. If targeted lab work points toward a specific cause, treatment options may include hormone therapy for women, testosterone therapy for men, wellness injections, or appropriate supplementation guided by actual lab results rather than guesswork. Learn more about how visits work to get started.

Trusted Sources

For further reading, the NIH National Institute on Aging discusses fatigue in older adults, the CDC offers information on sleep health, and the Endocrine Society publishes patient resources on thyroid function, testosterone, and menopause-related hormonal changes.