Why Am I So Tired? Biological Factors Affecting Women

Why do women often feel more tired than men? It’s a question many of us in demanding roles, like nursing, caregiving, and healthcare leadership, ask ourselves often. While long shifts, emotional labor, and societal expectations certainly play a role, the answer also lies deeper—woven into our biology. From monthly cycles to major life transitions, biological and hormonal shifts have a powerful impact on women’s energy levels.

Understanding these unique physiological factors isn’t just about having the knowledge—it’s about empowerment. When you understand what your body is going through, you can stop blaming yourself and start taking steps to protect and restore your energy.

The Menstrual Cycle and Energy Dips

Your monthly menstrual cycle is like a hormonal symphony, and the fluctuations directly affect how you feel. The two main players are estrogen and progesterone. As they rise and fall, they influence energy, mood, sleep, and even motivation.

The Luteal Phase Drain

The two weeks before your period—called the luteal phase—are when many women notice their energy dipping the most. After ovulation, progesterone levels rise sharply. This hormone is crucial for preparing the uterus for a possible pregnancy, but it also has a natural sedative effect. That’s why you might feel sluggish, less motivated, or crave more rest during this time.

To make matters more challenging, serotonin levels (a key mood-stabilizing neurotransmitter) tend to dip during the luteal phase. This drop contributes to PMS symptoms such as irritability, sadness, food cravings, and, yes, increased fatigue. Sleep disturbances are also more common in this phase, creating a vicious cycle where low mood, poor rest, and sluggish energy feed into each other.

Iron Loss During Menstruation

When your period begins, your body sheds its uterine lining. For women with heavy menstrual bleeding (menorrhagia), this blood loss can be significant. One of the biggest consequences? A decline in iron levels.

Iron is vital because it helps make hemoglobin—the protein in your red blood cells responsible for carrying oxygen throughout your body. Without enough iron, your cells literally can’t get the oxygen they need to function efficiently. The result? You feel wiped out both physically and mentally. Even mild iron-deficiency anemia can make everyday tasks feel like climbing a mountain, and it’s especially draining for women working 10- or 12-hour shifts in physically and emotionally demanding jobs.

Pro tip: If you feel persistently fatigued around your period, ask your healthcare provider about checking your iron levels. Iron-rich foods like spinach, red meat, beans, and fortified cereals can help, but supplementation may be needed in some cases (NIH ODS, 2022).

Perimenopause and Menopause: The Midlife Energy Shift

As women enter perimenopause (the transitional years before menopause), estrogen and progesterone levels begin to fluctuate unpredictably. These hormonal shifts can disrupt your sleep, mood, and energy. Hot flashes and night sweatscan wake you up multiple times at night, while mood swings and anxiety can make it harder to unwind at the end of the day.

By the time menopause arrives—defined as 12 months without a menstrual cycle—the decline of reproductive hormones often leaves women navigating a new baseline of energy. Insomnia, slower metabolism, and increased risk of thyroid dysfunction all add layers to the fatigue picture (Harvard Health Publishing, 2022).

The good news? Lifestyle adjustments like cooler sleep environments, stress reduction practices, balanced nutrition, and regular movement can go a long way in supporting energy. For some women, medical support such as hormone therapy may also be an option worth exploring with a trusted provider.

Pregnancy: When Growing a Life Drains Yours

Pregnancy is often described as beautiful, but let’s be real: it’s also exhausting. And there are biological reasons for that.

• First trimester: Rising progesterone makes you extra sleepy, while your body works overtime to support early development.

• Second trimester: Energy often rebounds, but your body is still producing more blood and nutrients to sustain your baby.

• Third trimester: Discomfort, disrupted sleep, and the physical demands of carrying more weight often bring fatigue back with a vengeance.

This isn’t weakness—it’s biology. Your body is creating an entirely new human being. Fatigue during pregnancy is not only expected but also a natural protective mechanism encouraging rest.

Thyroid Issues: The Hidden Energy Disruptor

The thyroid gland may be small, but it has a huge influence on energy. It regulates metabolism, heart rate, and even mood. Thyroid issues are far more common in women, especially after pregnancy or during midlife transitions.

• Hypothyroidism (underactive thyroid): Leads to sluggishness, brain fog, weight gain, constipation, and sensitivity to cold.

• Hyperthyroidism (overactive thyroid): Can create the opposite problem—anxiety, restlessness, insomnia, rapid heartbeat—often followed by an energy crash that feels like burnout.

Because thyroid symptoms overlap with so many other conditions, they’re easy to miss or dismiss. But if you’ve been feeling persistently tired and nothing seems to help, asking your doctor for a thyroid panel could give you answers (NIH, 2023).

Reproductive Stages and Their Toll on Energy

A woman’s life is marked by several distinct reproductive stages, each bringing its own set of hormonal changes that can profoundly affect energy levels. These shifts are not just emotional or psychological—they are deeply biological, affecting everything from metabolism to sleep patterns. Understanding them is key to showing yourself compassion and finding strategies that honor your body’s needs at each stage.

Pregnancy: Building a Life Takes Energy

Pregnancy is one of the most physically demanding experiences a woman’s body can undergo. In the first trimester, progesterone levels skyrocket to support the growing fetus. This surge in hormones, along with the body’s work to increase blood volume and build the placenta (an entirely new organ!), creates intense fatigue. Many women describe it as feeling like they’ve run a marathon without moving from the couch.

In the second trimester, energy often improves, but the body is still working overtime to sustain the baby’s rapid development. By the third trimester, fatigue typically returns as the growing baby places greater physical strain on the body. Sleep becomes challenging due to discomfort, frequent urination, and anxiety about the upcoming birth. It’s not just in your head—it’s your biology demanding rest while managing one of the most energy-intensive processes of human life.

Tip: Prioritize short naps and gentle movement. Even 15 minutes of stretching or walking can help with circulation and reduce fatigue.

Postpartum Depletion: The Perfect Storm

After childbirth, the body undergoes one of the most dramatic hormonal crashes in human physiology. Estrogen and progesterone levels drop significantly within the first 24 hours, a shift that can contribute to the "baby blues" or, in some cases, postpartum depression. Fatigue is one of the hallmark symptoms of both conditions (Harvard Health Publishing, 2023).

Layer on top of this the realities of newborn care: sleep deprivation, round-the-clock feeding, and the physical recovery from childbirth itself. It’s no surprise that many new mothers experience profound exhaustion that lasts for weeks or even months. This isn’t weakness—it’s biology. Postpartum depletion is a real condition, and recovery requires rest, support, and often medical follow-up to monitor iron levels, thyroid health, and mood disorders.

Tip: Ask for help unapologetically. Even short breaks can help your body begin to recover.

Perimenopause and Menopause: The Great Shift

Perimenopause, the transition into menopause, can begin in the late 30s or 40s and last several years. During this time, estrogen and progesterone levels don’t just decline gradually—they fluctuate dramatically. This hormonal rollercoaster can cause unpredictable cycles, mood changes, hot flashes, and night sweats that wreck sleep quality. Poor sleep, in turn, amplifies fatigue and irritability.

Estrogen plays an important role in how cells use energy and in regulating cortisol, the body’s primary stress hormone. When estrogen becomes erratic, your energy regulation and stress response systems can feel completely out of balance. By the time menopause (12 consecutive months without a period) arrives, low estrogen levels may contribute to ongoing fatigue, slower metabolism, and a general sense of being "off" (Harvard Health Publishing, 2022).

The good news? Lifestyle adjustments—like cooling your sleep environment, practicing relaxation techniques, and engaging in regular strength training—can make a meaningful difference. For some women, medical options such as hormone replacement therapy (HRT) can also help restore balance.

The Thyroid Connection: Your Body’s Energy Engine

The thyroid gland, a small butterfly-shaped gland in your neck, is your body’s master regulator of metabolism. It produces hormones (T3 and T4) that control how efficiently your body converts food into usable energy. When the thyroid is out of balance, fatigue is often the very first symptom.

Hypothyroidism: An Underactive Engine

Women are five to eight times more likely than men to develop thyroid problems (NIH, 2023). The most common is hypothyroidism, or an underactive thyroid. In this condition, the gland doesn’t produce enough thyroid hormone. As a result, everything in your body slows down: metabolism, circulation, digestion, and even brain function.

Symptoms include:

• Constant fatigue, even after sleep

• Weight gain or difficulty losing weight

• Sensitivity to cold

• Brain fog and memory problems

• Dry skin and brittle hair

Because these symptoms overlap with burnout, depression, or perimenopause, hypothyroidism is often overlooked. But the fatigue it causes can be crushing, making daily activities feel impossible. A simple blood test can diagnose the condition, and with proper treatment, many women experience significant relief.

Hyperthyroidism: Burnout in Overdrive

Less common but equally draining is hyperthyroidism, or an overactive thyroid. Instead of slowing everything down, the thyroid works in overdrive—causing anxiety, insomnia, racing thoughts, heart palpitations, and eventually exhaustion from being in a constant state of high alert.

Both conditions highlight the thyroid’s role as the body’s energy engine. When it’s not balanced, neither are you.

Tip: If your fatigue is persistent and unexplained, ask your healthcare provider for a complete thyroid panel, not just TSH. This ensures a clearer picture of how your thyroid is functioning.

Take the Next Step to Reclaim Your Energy

Understanding the biological reasons behind your exhaustion is empowering. It validates your experience and reminds you that fatigue isn’t a weakness or a flaw—it’s your body communicating with you. You are not imagining it, and you are certainly not alone. Your hormones, your life stage, and your overall physiological health are all deeply intertwined with your energy levels.

If this constant tiredness feels familiar, here are some steps you can begin taking right now:

1. Track Your Energy Patterns

Start by keeping a fatigue journal for at least one month. Note your energy levels throughout the day, your menstrual cycle phase (if applicable), your sleep quality, and any emotional stressors. Patterns often emerge: maybe you notice that your energy dips predictably in the luteal phase, or that poor sleep triggers two days of fatigue afterward. This awareness helps you connect the dots and plan ahead.

2. Partner With Your Healthcare Provider

Bring your notes to a trusted provider. Ask about checking for:

• Iron levels (especially if you have heavy periods)

• Vitamin B12 and vitamin D levels

• Thyroid function tests (TSH, Free T3, Free T4)

• Hormonal assessments if you suspect perimenopause, menopause, or polycystic ovarian syndrome (PCOS)

A simple blood test can often uncover hidden contributors to your fatigue. Getting clarity here can be life-changing.

3. Explore Supportive Interventions

Once you have more information, you can begin layering in changes that address both symptoms and root causes. This might include:

• Nutrition adjustments (iron-rich foods, balanced meals)

• Gentle but consistent physical activity

• Stress management practices like yoga, breathwork, or meditation

• Medical treatment for conditions like anemia, thyroid imbalance, or perimenopausal symptoms

4. Build Your Support System

Fatigue can feel isolating, especially if others don’t understand why you’re so tired. Surround yourself with supportive people—friends, family, or peer groups who can encourage you, share their own experiences, and remind you that rest is not selfish.

5. Give Yourself Permission to Rest

This is perhaps the hardest step, especially for women in caregiving or leadership roles. But honoring your body’s need for rest is a radical act of self-care. Your worth is not defined by how much you can push through. It’s okay to slow down.

Final Word

Recognizing the why behind your fatigue is your first, most powerful step toward balance and vitality. From there, you can begin building a plan—one rooted in self-awareness, evidence-based strategies, and compassionate care.

You don’t have to live in survival mode. Step by step, with the right tools and support, you can reclaim your energy and feel more like yourself again.

Your energy is precious. Let this be the moment you choose to protect it, nurture it, and take the next step toward reclaiming it.