Why Fit, Active People Still Struggle with Fatigue: The Role of B12, Iron, and Hormones

You train hard. You prioritize clean eating. You might even track your macros, sleep, and hydration. And yet, fatigue still lingers. Energy crashes, poor recovery, brain fog, or feeling "off" even when labs say you're "normal."

OR, even worse (which this has happened to me), you’re super active and fit and all of a sudden you’re getting winded and short of breath a few minutes or a few reps into your workout wondering what the heck is going on.

For athletic and active individuals, this isn’t just frustrating—it can sabotage progress, motivation, and long-term health. What most people (and many doctors) overlook is that the more active you are the higher the metabolic and micronutrient demands you will have.

Two critical and often-overlooked nutrients in active individuals that are crucial to energy production, red blood cells, and oxygen? Vitamin B12 and Iron.

Why B12 and Iron Are Crucial for Active Individuals

Vitamin B12 (cobalamin) and Iron are essential for oxygen transport, red blood cell production, neurological function, and energy metabolism. They are also a huge part of the inflammation process when you workout in helping produce red blood cells to repair your body. When you’re constantly inflamed (from working out) your body has to go into your iron stores to grab red blood cells full of nutrients to help in the repair process if you are not properly recovering and properly fueling.

Vitamin B12 is in important nutrient in numerous functions throughout the body:

• Involved in methylation, detox, liver health, DNA synthesis, red blood cell formation, and myelin sheath maintenance (part of nerve health)

• Essential for energy production in mitochondria, the "power plants" of your cells

• Deficiency can result in fatigue, weakness, poor coordination, always feeling cold, sleep disturbances, memory problems, and mood disturbances

Iron:

• Central to hemoglobin, which transports oxygen to muscles and tissues

• Critical for endurance, aerobic output, and thermoregulation

• Deficiency (even borderline) impairs VO2 max, mitochondrial function, and increases perceived exertion

If you're experiencing low energy, recovery issues, or brain fog, it's time to go beyond basic labs and get real data by looking under the hood specifically for someone who is active and athletic. → Download my FREE guide: Top 3 Functional Labs Every Active Person Needs 

Why Athletes Burn Through These Nutrients Faster

Training increases your demand for both iron and B12 due to:

• Higher red blood cell turnover from repeated physical stress

• Increased sweat loss and minor bleeding from endurance training

• Greater mitochondrial activity, which relies on both nutrients for ATP production

• Heightened nervous system activation, requiring more B12 for neurotransmitter synthesis

Women, especially active women of reproductive age, are at higher risk due to menstrual blood loss and often under-diagnosed iron deficiency (even without anemia). If you are an active or athletic woman who tends to have heavy periods, you may also have an underlying B12/Iron (and Vitamin C) deficiency. Vitamin C & B12 are important for Iron absorption and if there is a borderline iron deficiency they also come paired with low levels of Vitamin C & B12.

How Iron & B12 Levels Affect Your Hormones

Hormones like thyroid (T3/T4), cortisol, and estrogen/testosterone directly interact with your nutrient metabolism:

• Low Iron can reduce conversion of T4 to active T3, impairing metabolic rate and energy

• B12 deficiency impacts adrenal health, compounding stress and cortisol dysregulation

• Sex hormones influence iron status: Estrogen may reduce hepcidin (a regulator of iron absorption) which is why your iron levels and needs change throughout perimenopause and menopause with fluctuating levels of estrogen, while high cortisol can suppress absorption and increase demand

Imbalanced hormones, especially in overtrained or under-recovered athletes and fitness enthusiasts, further deplete B12 and iron stores—creating a vicious cycle of fatigue, poor recovery, and stalled progress.

Want a data-driven plan to correct your nutrient and hormone imbalances? Apply now for PR Fuel — my signature Integrative Hormone Health program built for athletes and active humans. 

Why Your Doctors Standard Labs Miss the Mark

Your doctor may run a CBC, serum B12, or ferritin test and say, "You're fine." But here's the truth:

• Serum B12 doesn’t reflect cellular B12 levels. You need MMA (methylmalonic acid) and homocysteine for functional insight.

• Ferritin alone is not enough. You need serum iron, transferrin saturation, and TIBC (Total Iron Binding Capacity) to fully assess iron metabolism.

• "Normal" lab ranges are based on sedentary populations—not people who train hard and push their limits.

• Your doctor is looking for disease and dysfunction to make sure there isn’t a serious health emergency…not for optimal levels for your overall functional health.

Functional ranges (what we use in PR Fuel) are optimized for thriving, balance, personalization, and performance, not just survival.

Stop guessing. Start testing. Apply for PR Fuel and finally uncover what's draining your energy and holding your body back.

Signs You May Be Dealing with an Iron or B12 Deficiency (Even Without Anemia)

• Fatigue, especially post-exercise

• Cold hands/feet, pale skin, or brittle nails

• Shortness of breath or elevated heart rate during normal training

• Brain fog or poor mental endurance

• Frequent injuries or slow wound healing

• Anxiety, low motivation, or poor sleep quality

Even subclinical deficiencies can limit performance, suppress recovery, and sabotage your gains.

For years, in highschool and college as an athlete I would get these weird bouts of what felt like anxiety attacks where I would get real shaky, feel like I was going to pass out, and almost a nervous energy. Everyone kept misdiagnosing me with low blood sugar (because nobody was testing…they were guessing), and even when I ate right before a game or practice I’d still get these weird experiences.

This lasted for years until finally I started learning about Integrative and Functional Health and researched B12 and Iron deficiencies in female athletes and found out that I wasn’t struggling with anxiety-I was struggling with low Iron that mimicked those symptoms. 

At first I was frustrated wondering why it took years of research and no one put forth the energy of running any kind of deeper lab work. Then I became very passionate about Integrative Health for active men and women because I knew other people were out there struggling with these “mysterious symptoms” that traditional doctors just weren’t trained in and weren’t doing the work to help fix the root cause.

The PR Fuel Approach: Test, Rebuild, Perform

PR Fuel is not another supplement list, diet, shiny program or one-size-fits-all protocol. It's a strategic system that uses:

• Advanced functional lab testing (including intracellular B12, full iron panel, thyroid, adrenals, and sex hormones)

• Personalized nutrition planning based on your metabolic needs

• Targeted repletion protocols to restore critical nutrients

• Ongoing coaching and data tracking to monitor your recovery and progress

• Integrative Hormone Health to optimize and fix your hormones so you can get back to being energized, feeling like your best self, hitting PR’s in the gym and in life

This isn’t about chasing symptoms—it’s about rebuilding the systems that fuel your athletic potential.

Ready to train harder, recover smarter, and feel like yourself again? Apply now for PR Fuel and let’s uncover the root of your issues. 

Final Thoughts

Fatigue isn’t just about working too hard or not sleeping enough. For athletes and active individuals, it's often about unmet physiological demand. B12, Iron, and hormone imbalances are some of the most under-addressed, yet critical pieces of the performance puzzle.

You can’t out-train a deficiency. But you can test for it, fix it, and come back stronger.

Here’s to fueling your best self,

Ashley Drummonds