Why Am I So Tired All the Time? A Physician’s Guide to Fatigue in Your 40s

If you’re a high-capacity woman doing everything—career, kids, aging parents, relationships, and the endless “life logistics”—and still quietly thinking, “Why am I so tired all the time?” …you’re not alone.

When you say you’re tired, friends might laugh and say, “Welcome to your 40s!” But as a physician, I want to offer a different perspective: some fatigue is common in this season of life, but persistent exhaustion isn’t something you should automatically accept as normal.

This post walks through the same framework I use in clinic when a patient’s energy isn’t keeping up with her agenda—and what you can do next.

What does “tired all the time” actually mean?

People use “tired” to describe different experiences:

• Sleepiness (you could fall asleep anytime)

• Low energy (your battery feels drained even after rest)

• Brain fog (slower thinking, trouble concentrating)

• Low stamina (exercise feels harder than it used to)

If you’re noticing fatigue most days for a few weeks or longer, especially if it’s new for you, it’s worth looking for patterns and possible medical contributors.

The most common reasons women in their 40s feel exhausted

1) The perimenopause factor

For many women, perimenopause is the “missing puzzle piece.” Hormonal shifts can start years before the final period and don’t just affect your cycle—they can impact sleep, mood, temperature regulation, and cognition.

Common clues include:

• Period changes (heavier, closer together, farther apart, unpredictable)

• New insomnia or 3 a.m. wake-ups

• Night sweats/hot flashes

• Increased anxiety or irritability

• Brain fog that feels new

If you think perimenopause could be contributing, consider talking with a clinician who is comfortable discussing the full range of options: lifestyle changes, non-hormonal supports, and—when appropriate—hormone therapy.

2) Iron deficiency (even without anemia)

Many women assume: “My CBC was normal, so my iron is fine.” However, clinical data shows that 38% of non-pregnant women are iron deficient without being fully anemic. If you have heavy periods—common during the 40s—your iron stores (ferritin) may be depleted. Heavy menstrual bleeding is a major contributor to iron deficiency - and heavy or prolonged periods can become more common in the menopause transition.

Low iron stores can cause:

• Exhaustion

• Exercise intolerancze

• Shortness of breath with exertion

• Hair shedding

• Brain fog / poor concentration

• Restless legs
  

What to ask your clinician:
Consider checking ferritin and iron studies (not just a hemoglobin).
Important: don’t start long-term iron supplementation without guidance—too much iron can be harmful, and the best plan depends on your labs and your symptoms.

3) Metabolic shifts: thyroid + blood sugar changes

Your 40s are a common time for “metabolic clues” to start showing up—especially if sleep and stress are already stretched thin.

Thyroid (hypothyroidism) can cause:

• Fatigue and brain fog

• Weight changes

• Constipation

• Dry skin and hair changes

• Feeling cold more easily
  
  

Blood sugar dysregulation can also show up as:

• A profound afternoon slump

• Feeling “shaky” or irritable when you haven’t eaten

• Sugar cravings

• Energy spikes and crashes
  

What to ask your clinician:

• TSH (thyroid screen)

• HbA1c and/or fasting glucose (diabetes/prediabetes screening)
  If symptoms suggest it, it can also be reasonable to discuss early insulin resistance and lifestyle strategies that support steadier energy.

4) Depression and anxiety (often feels like exhaustion first)

In real life, many women don’t come in saying “I’m depressed.” They say:

• “I’m exhausted.”

• “I can’t focus.”

• “I feel numb.”

• “I’m not myself.”

Mood concerns can present as very physical symptoms—especially when you’re carrying a lot.

Consider support if you’re noticing:

• Persistent overwhelm or irritability

• Feeling on edge, tense, or “wired but tired”

• Difficulty enjoying things you normally like

• Sleep or appetite changes

• Concentration issues
  

A primary care doctor can screen for depression/anxiety (often with tools like the PHQ-9) and help you explore next steps—therapy, coaching, lifestyle supports, and when appropriate, medication.

5) Sleep apnea (yes—women too)

Sleep apnea is often underdiagnosed in women because symptoms don’t always match the stereotype.

Women may not describe classic “I fall asleep everywhere” sleepiness. Instead they may have:

• Fatigue and low energy

• Unrefreshing sleep

• Morning headaches

• High blood pressure

• Increased nighttime urination

• Snoring (sometimes, but not always)
  

If this sounds familiar, ask your doctor whether a sleep study makes sense. Treating sleep apnea can be a game-changer for energy, mood, and long-term heart health.

6) Chronic stress and burnout (your nervous system is overworked)

Burnout isn’t weakness. It’s what happens when chronic stress outpaces recovery—especially when your brain and body never truly get “off-duty.”

Clues include:

• Feeling emotionally depleted

• Cynicism/irritability you don’t recognize in yourself

• “I can’t turn my brain off”

• Sleep that’s light, fragmented, or never restorative
  
  

What helps in real life (not perfection):

• Micro-recovery: 5–10 minutes between tasks without screens

• Boundaries: reducing after-hours mental labor when possible

• Support: therapy/coaching, workload redesign, and redistributing invisible labor (even small shifts matter)
  
  

7) Too much sitting + not enough strength or cardio

When life gets busy, movement is often the first thing to go—and energy suffers. An increase in sedentary behavior can directly decrease cardiorespiratory fitness, reduce total muscle mass and strength/capacity, and increase insulin resistance and metabolic changes that manifest as fatigue and low energy.

Here’s the encouraging part: movement creates energy, especially in midlife. Even small doses count.

If you find that being busy means more sitting - try one (or all) of these:

• 10-minute walk after meals

• 2–3 short strength sessions per week (15–20 minutes still “counts”)

• 2–3 minutes of movement every hour during the workday
  
  

Don’t miss this: When heart disease can look like fatigue

Women are more likely to NOT present with the classic symptoms of heart attacks - crushing chest pain or chest pressure. Sometimes fatigue, decreased exercise intolerance, or uncharacteristic breathlessness can be signs of heart disease or early heart failure.    

Consider seeking medical evaluation sooner if you have:

• New or worsening shortness of breath

• Chest pressure/tightness (even subtle), nausea, sweating, jaw/arm discomfort

• Noticeably decreased exercise tolerance

• Swelling in the legs, needing extra pillows to sleep, or waking up breathless
  

If you’re unsure, it’s appropriate to ask your clinician for a cardiovascular risk assessment based on your symptoms and risk factors.

A practical checklist to bring to your appointment

If fatigue is persistent, your clinician may ask about:

• Period changes (heavier? irregular? skipped?)

• Sleep quality (snoring? waking up? unrefreshed?)

• Mood (anxiety, numbness, loss of joy, concentration changes)

• Thyroid clues (weight change, cold intolerance, hair/skin changes)

• Exercise tolerance and shortness of breath

• Diet pattern (especially protein + iron sources

• Stress load and recovery time

• Medications and supplements (including OTC)
  

Common starting labs often include:

• CBC

• Ferritin + iron studies

• TSH

• HbA1c and/or fasting glucose

• CMP (metabolic panel)

• Lipids (depending on age and risk factors)
  
  

A final note

If this list feels a bit overwhelming, I get it.

This post isn’t meant to make you feel like you have to diagnose yourself or “fix it all” alone. It’s meant to validate your symptoms and encourage you that it is possible to find answers and real solutions to your symptoms.  

Fatigue in midlife is often complex, nuanced, and multifactorial - hormones, nutrients, sleep, stress, mood and metabolism all overlap.  By working with a physician you trust, you can make real steps towards progress.    

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Frequently Asked Questions

Why am I so tired all the time in my 40s?
Common causes include perimenopause-related sleep disruption, low iron, thyroid changes, blood sugar issues, anxiety/depression, sleep apnea, chronic stress/burnout, and too little movement.

Can iron be low even if I’m not anemic?
Yes. Ferritin and iron studies can be low even when hemoglobin is normal, especially with heavy periods.

Is fatigue a symptom of perimenopause?
Yes. Many women report fatigue and brain fog during the menopause transition, often tied to sleep disruption and hormonal fluctuations.

Could sleep apnea cause fatigue without daytime sleepiness?
Yes. Many women experience unrefreshing sleep, fatigue, headaches, and nighttime urination rather than obvious sleepiness.