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When I was in medical school, I often thought about all the puzzles I’d be solving for patients. How would I handle all the different ailments that might walk through my office doors? My 20-something self would’ve never guessed that 90% of patients would be complaining about the very same thing — they’re so tired.
“My 20-something self would’ve never guessed that 90% of patients would be complaining about the very same thing — they’re so tired.”
So why is it that nearly 1 in 4 women report feeling fatigued most days of the week? Why are women almost twice as likely as men to experience chronic exhaustion and sleep disruption? And why, despite getting close to the recommended seven to nine hours of sleep, do so many women wake up feeling like they never rested at all?
From a conventional lens, fatigue is often chalked up to stress, busy schedules, or “just part of life.” But from a functional medicine perspective, persistent exhaustion is rarely random — and almost never meaningless.
Fatigue is a signal that too many women simply ignore. I’ve had far too many patients see me for the first time and tell me they’ve been tired for months, if not years, before they even consider it something to discuss with their doctor.
It can reflect hormone shifts that begin years before we label them “perimenopause.” It can point to iron depletion long before anemia is diagnosed. It can be tied to blood sugar instability, thyroid patterns hovering just inside “normal,” chronic inflammation, micronutrient deficiencies, or a nervous system that has been running in overdrive for too long. In my own story, it was one of the only signs I was dealing with before being diagnosed with breast cancer in my early 30s.
In other words, fatigue can be more than simply needing better rest: It can indicate your biology is carrying more load than it can sustainably replenish.
One of the most common drivers of fatigue I see isn’t a single lab abnormality. It’s accumulated chronic stress.
And I don’t just mean emotional stress.
From a physiologic perspective, stress includes blood sugar swings, sleep disruption, under-fueling, inflammation, over-exercising, nutrient depletion, environmental exposures, and the constant cognitive load many women carry. The body doesn’t distinguish between a tense email and a skipped meal — both register as demand.
“The body doesn’t distinguish between a tense email and a skipped meal — both register as demand.”
When demand consistently outpaces recovery, the nervous system shifts into survival mode. Cortisol rhythms begin to flatten, causing your hormonal symphony to get out of balance. Sleep becomes lighter and less restorative. Energy turns volatile. You may feel wired at night and foggy in the morning. Coffee starts to feel less optional and more necessary.
You may have heard the term “adrenal fatigue,” but that label doesn’t fully capture what’s happening. What we’re really seeing is Hypothalamic-Pituitary-Adrenal (HPA) axis dysregulation: a disruption in how the brain and adrenal glands communicate under chronic stress. The result is a body that is technically awake, but not deeply restored.
Chronic stress exhausts you mentally, emotionally, and physically. It’s not just in your head. In my practice at Love Life, I look for where that exhaustion is stemming from and how to bring it back. That often begins by helping the body move from constant, high-alert stress to something more sustainable — everyday, manageable stress. And yes, there is a difference.
And restoring that difference is where real healing starts.
Taking a look at iron deficiency
If I had to name the most overlooked nutrient cause of female fatigue, it would be iron depletion. It’s notoriously missed in conventional medicine because as long as you aren’t technically anemic, the conversation often stops there.
In functional medicine, we look at optimal ranges, not just whether a value falls inside a wide reference interval. A woman can have a “normal” hemoglobin level and still have ferritin (her iron storage marker) that is too low to adequately support energy production.
Women are particularly vulnerable to iron depletion due to menstruation, pregnancy, postpartum recovery, certain diets, endurance training, and chronic inflammation. Heavy periods alone can gradually lower iron stores over years, often without anyone noticing until symptoms become disruptive.
“Women are particularly vulnerable to iron depletion due to menstruation, pregnancy, postpartum recovery, certain diets, endurance training, and chronic inflammation.”
Iron is essential for oxygen delivery at the cellular level. When iron stores are low, your cells quite literally receive less oxygen. The result can be persistent fatigue, shortness of breath with exertion, hair shedding, cold intolerance, brittle nails, anxiety, and brain fog.
I can’t tell you how many women I’ve seen regain clarity and stamina after correcting iron stores that were technically “normal,” but far from optimal.
That said, simply adding an iron supplement isn’t always the right first step. Iron status should be properly evaluated with a full iron panel with your doctor before supplementing, since excess iron can also create problems. A registered dietician and health coach can support a food diary review to understand your iron intake and ways to support healthy digestion. For many women, beginning with iron-rich foods is a supportive and safe foundation, especially during seasons of increased demand.
Iron-rich foods include:
- Grass-fed red meat and liver
- Dark meat poultry
- Sardines and shellfish
- Lentils and beans (paired with vitamin C for better absorption)
- Spinach and other dark leafy greens
Supporting iron absorption by including vitamin C–rich foods and avoiding excessive calcium or coffee at iron-rich meals can make a meaningful difference too.
Blood sugar instability (even without diabetes)
If you haven’t heard much about balancing blood sugar, this one may be a game-changer.
Blood sugar volatility refers to repeated spikes and crashes in glucose levels throughout the day. Even if your fasting glucose is “normal,” you can still experience significant fluctuations after meals — especially when meals are low in protein and fiber or spaced too far apart.
“You can still experience significant fluctuations after meals — especially when meals are low in protein and fiber or spaced too far apart.”
Skipping meals, relying heavily on caffeine, under-eating protein, or grazing on high-carbohydrate snacks can all create subtle surges followed by dips. Each dip triggers a stress response. Cortisol rises to bring blood sugar back up, which further strains the system.
Over time, this internal rollercoaster can leave women feeling:
- Shaky or anxious between meals
- Ravenous at night
- Foggy mid-afternoon
- Energized late in the evening
- Exhausted but unable to sleep
Blood sugar stability is foundational to energy because it directly influences metabolic function. When glucose and insulin patterns are erratic, your mitochondria (the cellular engines responsible for producing energy) cannot operate efficiently. The result is a body that’s technically fueled, but still fatigued.
Balanced meals that include adequate protein, fiber, and healthy fats, eaten at consistent intervals, often improve energy more effectively than any supplement. Before adding something new, sometimes we need to stabilize what’s already there.
Hormonal transitions that start earlier than you think
Perimenopause doesn’t always begin when you expect it to. For many women, subtle hormonal shifts start in their late 30s or early 40s and sometimes earlier. These shifts are happening long before anyone uses the word “menopause.”
Fluctuations in estrogen and progesterone can quietly affect sleep quality, mood stability, body temperature, and insulin sensitivity. Progesterone, in particular, has calming effects on the nervous system. When it begins to decline, women may notice lighter sleep, increased nighttime awakenings, or feeling more “wired” before bed — even if hot flashes aren’t present yet.
“Fluctuations in estrogen and progesterone can quietly affect sleep quality, mood stability, body temperature, and insulin sensitivity.”
Hormones also don’t operate in isolation. Estrogen influences thyroid function, thyroid hormones regulate metabolism, and both affect how efficiently your body produces energy. Even subtle shifts can leave you feeling depleted, foggy, or not quite like yourself — sometimes while labs are still technically “normal.”
Postpartum recovery is another often-overlooked chapter. Nutrient depletion, sleep fragmentation, blood loss during delivery, and the metabolic demands of breastfeeding can leave women exhausted for months — sometimes years — without structured support. And yet many are told this is simply part of motherhood.
Too many women push through hormonal changes as if they’re supposed to just soldier on.
You don’t have to.
Hormonal transitions are normal. Ignoring the signals your body sends during those transitions is not. When hormones fluctuate (and they will) energy fluctuates with them. Paying attention early, rather than waiting until you’re completely depleted, can make a profound difference.
Micronutrient deficiencies, mitochondria, and circadian rhythm
When women are tired, the default advice is often, “Just go to bed earlier.” And while sleep absolutely matters, that’s not the full picture.
Energy isn’t created when your head hits the pillow, and thank goodness for that! It’s created all day long.
The most foundational system driving how energized you feel is your metabolic health, and that’s not just about weight or “having a fast metabolism.” It’s about how efficiently your body produces energy at the cellular level.
“The most foundational system driving how energized you feel is your metabolic health.”
Energy production happens inside structures called mitochondria. These are the tiny engines within your cells responsible for converting nutrients into usable energy. And mitochondria require specific vitamins, minerals, and cofactors to function well.
Common deficiencies I see in fatigued women include:
- Vitamin D
- Magnesium
- Vitamin B12
- Folate
- Omega-3 fatty acids
These nutrients support cellular energy production, nervous system regulation, and inflammation control. Without them, energy production becomes less efficient, even if you’re eating enough calories.
Chronic stress, gastrointestinal issues, restrictive diets, poor protein intake, and certain medications can quietly deplete these nutrients over time. And then there’s your circadian rhythm, which is the internal clock that tells your body when to be alert and when to restore.
“Your mitochondria don’t just need nutrients; they need better timing.”
Your mitochondria don’t just need nutrients; they need better timing. Exposure to morning light, consistent meal timing, movement during the day, and reduced light exposure at night all help regulate your circadian rhythm.
When that rhythm is disrupted by late-night scrolling, irregular sleep schedules, never getting outdoors except when you’re commuting, or chronic stress — your energy production becomes less synchronized.
Fatigue in survival mode
Fatigue doesn’t always look like collapse or wishing you could have better sleep. Sometimes it looks more like anxiety.
When the nervous system remains in a prolonged fight-or-flight state, sleep becomes lighter, digestion slows, and restorative processes are deprioritized. You might feel “tired but wired.” Exhausted, but unable to fully relax. In this state, even seven or eight hours of sleep doesn’t translate into true restoration.
“This is why energy is never just about sleep duration. It’s about regulation.”
This is why energy is never just about sleep duration. It’s about regulation.
And that’s the deeper point. When women are tired, they often blame themselves. They assume they need more discipline, more productivity, more resilience. But most of the time, it’s more about our capacity and not our character. You don’t have to be so hard on yourself if you’re tired.
Fatigue, no matter where it’s coming from, is simply information. It tells us that demand has exceeded reserve. It tells us that something upstream needs attention.
“Fatigue, no matter where it’s coming from, is simply information.”
So if you’re still trying to push through your fatigue, I’d like you to stop judging yourself for being tired and just pause. It’s okay to listen to the signals. Because if we’re brave enough to look upstream, exhaustion that once felt mysterious becomes understandable. And what becomes understandable becomes treatable.
Dr. Jaclyn Tolentino is a Board-Certified Family Physician and the Lead Functional Medicine Physician at Love.Life. Specializing in women’s health and hormone optimization, she has been featured in Vogue, The Wall Street Journal, and Women’s Health. As a functional practitioner and a breast cancer survivor, Dr. Tolentino is dedicated to uncovering the root causes of health challenges, employing a holistic, whole-person approach to empower lasting wellbeing. Follow her on Instagram here for more insights.
