Why Your Iron Is Still Low (Even Though You're Taking Supplements)

Written by Sarah Bishop, MS Exercise Science, Functional Health Coach

Iron deficiency is common, especially in active females. You may have personally experienced the impacts in not just your training, but everyday life of iron deficiency or anemia (which aren't the same and I will explain more below!) and know the feeling of dragging through. 

But is taking a supplement always the right solution? What about long term? What if you are taking a supplement but still have low levels…?

 That last one should raise red flags- and was the question that prompted this blog post. “My client is taking a multivitamin with iron , but her levels are still low and she’s struggling with hair loss and fatigue. ” 

  Let’s dig into why iron supplements may not always work, how iron functions in the body, and what to consider before supplementing.

What's the difference between iron deficiency and anemia?

Anemia is a general term for having fewer red blood cells or a reduced amount of hemoglobin in each red blood cell. This results in insufficient oxygen being delivered to tissues. While iron deficiency anemia (IDA) is the most prevalent form, other types of anemia, like megaloblastic anemia (often caused by B12 or folate deficiency), can also contribute to low iron levels.Iron is crucial for energy production and oxygen transport. If you have ever dealt with iron deficiencies, you know the feeling of trying to live life, let alone train depleted. 

Anemia is a symptom, not a diagnosis, and should prompt further investigation into underlying causes. It’s not just about low iron. Other factors, such as inflammation, stress, or nutrient deficiencies, may play a role.

Symptoms of low iron

• Extreme fatigue or low energy
• Unexplained weakness
• Pale skin
• Chest pain, fast heartbeat, or shortness of breath, especially when active
• Headaches, dizziness, or lightheadedness
• Cold hands and feet
• Brittle nails or hair loss
• Heavy menstrual bleeding (which can also be a cause)
• Unusual cravings, including for ice

Understanding Iron Metabolism and Absorption

The body has an intricate system for regulating iron absorption, transport, and storage. For example:

• Hepcidin is a key hormone in this process, and the "master regulator" of iron homeostasis.  When your iron is low, hepcidin drops so your body can absorb more. When iron is high, or when inflammation is present, hepcidin rises and blocks absorption to prevent overload
• Iron Absorption occurs primarily in the duodenum. However, conditions like low stomach acid, inflammation, or gut infections (such as H. pylori) can impair this process.

When iron is Stuck in Storage 

Absorbing iron is only step one. Your body also has to transport and recycle it. The protein responsible for this is ceruloplasmin. Ceruloplasmin is a copper-carrying protein made in your liver, and it needs copper and vitamin A to be built. It runs several jobs : it transports copper, it helps oxidize iron so iron can be picked up and moved, and it acts as an antioxidant when your body is under stress or fighting infection. For iron specifically, its main job is mobilizing iron out of tissue storage and into your blood, where you can actually use it.

Since ceruloplasmin helps your body regulate iron and keep it moving, not having enough bioavailable copper and vitamin A, liver issues, or conditions such as Wilson’s disease or a genetic condition called aceruloplasminemia can leave you making less of it. Now iron can’t get out of “storage mode” 

 If the transport system is the bottleneck, more iron just gives you more to store. Copper that is too low, or not in a usable form, strands iron in the tissues. Vitamin A works right alongside it, and a shortfall is linked to iron piling up in the liver and storage sites while your blood stays low.

Where to get these from food:

• Copper: organ meat, oysters, cod liver oil, spirulina, dark chocolate, sunflower seeds, potatoes, and mushrooms

• Vitamin A: liver, cod liver oil, dairy, ghee, and seafood, plus carrots, sweet potato, leafy greens, and squash

One caution: more is not automatically better. High-dose vitamin A supplements can work against you, so food comes first, and any supplementing is worth running by your provider. Iron, copper, and vitamin A move as a team, so a low iron result is usually a signal to look at the whole system rather than one number. Check your multivitamins, too: high-dose zinc depletes copper, which can interfere with iron recycling.

What causes low iron in active women?

Several things, often more than one at a time:

• Blood Loss: Heavy menstrual bleeding, gastrointestinal bleeding (due to conditions like Crohn’s disease or ulcers) can deplete iron stores.
• Dietary Deficiency: A diet lacking in iron-rich foods, especially heme iron from animal sources (e.g., red meat, organ meats), can result in iron deficiency. While non-heme iron from plant sources (like beans and spinach) is beneficial, it’s less efficiently absorbed. I suggest cronometer.com to check for any holes in your habitual diet. 
• Of note, one can be not clinically deficient but still getting an inadequate amount of nutrients for their needs.  Falling below adequate levels may not show up when reviewing labs as obviously as a frank deficiency would. BUT this is where a functional health approach is different. Optimal is different than adequate. Our goal isn’t just about avoiding disease, but ensuring the body is getting (and absorbing) the macronutrients and micronutrients needed to truly thrive at every level.  
• Poor Absorption: Conditions like low stomach acid, Celiac disease, or chronic inflammation (e.g., IBD) can impair nutrient absorption.
• Increased Demand: During periods of growth, like pregnancy, or intense exercise, the body’s iron requirements increase!
• Missing Nutrient Synergy: Iron metabolism relies on other nutrients like vitamin A, B vitamins, and copper. Shortfalls in these can impair iron absorption and recycling.

Why isn't my iron supplement working?

Popping iron pills seems like the obvious solution when iron levels are low, but it often misses the real issue. The most common reason is that something is impacting absorption or recycling issues are leaving iron out in the blood stream but it’s not entering the tissues and able to be used   Here’s the usual culprits :

• Absorption Issues: Iron supplementation won’t do much if the body isn’t able to absorb the iron properly. Low stomach acid, gut inflammation, or infections like H. pylori can block iron from being absorbed from the gut, no matter how much you take. Gut issues are common culprits, but they’re often overlooked, and fixing the gut comes before just adding more iron.
• More Training = Great Demands - Intense training raises hepcidin, a hormone that blocks iron absorption In general, athletes need more of a lot of other micronutrients too. Assessing diet first – including carbohydrate intake ( many women aren’t eating enough carbs!) might be a better first step before any supplements. Low carbs can mess with your iron absorption too, especially in athletes.
• Partner nutrients are missing: Iron doesn't work alone. It depends on copper, vitamin A, and B vitamins to be properly absorbed and recycled. Without those, iron might just sit there, unused, or worse, end up accumulating in tissues, which isn’t helpful.
• Inflammation & Stress: Chronic inflammation keeps hepcidin elevated. That inflammation doesn't have to come from injury. Poor sleep, ongoing stress, and low-grade gut issues all contribute.stemming from things like poor sleep, stress, or an underlying infection or autoimmune condition 
• Impaired Liver Function: The liver plays a huge role in iron metabolism. If there’s an issue with liver function (think inflammation, poor digestion, or gut infections), iron won’t be properly transported or recycled. So, if you're dealing with liver stress, taking iron supplements may make things worse because of that impaired recycling system. 
• Heavy Menstrual Bleeding: Yes, excessive bleeding leads to iron loss, but it's also a sign that something’s off. If you’re experiencing heavy periods, iron supplements might be the immediate fix, but the root cause of the bleeding needs to be addressed too.
• Too much without monitoring. : Iron supplementation, without monitoring ferritin levels, can lead to oxidative stress and gut irritation. In some cases, iron overload can even cause iron to accumulate in tissues, making things worse. This is why it's essential to not only supplement but also monitor iron storage carefully with follow up lab work.

What should I do before taking an iron supplement?

Work through these first. In many cases they resolve the issue, and they always make any supplement you do take more effective.

• Test First: Iron deficiency can exist for a long time before it shows up as anemia on a standard blood test, so a normal CBC alone doesn’t rule it out. A comprehensive iron panel (serum iron, ferritin, and transferrin saturation) gives you a much earlier and clearer picture, since ferritin reflects your stored iron and transferrin saturation can flag a problem before it becomes full anemia. Landing inside the lab’s ‘normal’ range and being optimal are two different things, and optimal comes down to the individual. As a general functional range, we want to see serum iron around 70-130 µg/dL and ferritin around 50-100 ng/mL. Run the full picture alongside it, including your CBC, CMP, and thyroid panels, since symptoms overlap heavily. Consider having ceruloplasmin, serum copper, and zinc measured . And remember, never test just to test. Test with question in mind that you are looking for an answer for and ensure you have support in interpreting any results 
• Support Gut Health: Iron won’t get where it needs to go if your gut can’t absorb it. Poor gut health, including increased intestinal permeability ( leaky gut)  or gut infections (like H. pylori or Candida), mess with absorption. Fixing the gut is key! No amount of supplementation will replace a healthy digestive system. Focus on healing the gut lining and reducing inflammation from the inside out. A good, solid digestive system is your first line of defense.
• Cover the partner nutrients.Iron depends on copper, vitamin A, and B vitamins, we can leverage food and meals to support optimal status of not just iron, but vitamins and minerals as a whole.  For example, pairing plant-based iron with vitamin C (like spinach and orange) can enhance absorption. Make sure they’re getting enough copper and vitamin A to avoid disrupting the entire system. Vitamins and minerals are a team effort!
• Lower  Inflammation: If inflammation is causing low iron absorption, it’s important to dig deeper into the sources—under eating (calories and micronutrients ) chronic stress, gut health, or even sleep quality. Once you address the root causes of inflammation, the iron can do its job more effectively. It’s not just about addressing low iron; it’s about fixing the environment in the body that’s preventing iron from doing what it needs to.
• Whole Foods Over Supplements: Aim to increase whole food sources of iron first. Red meat, poultry, organ meats, eggs, oysters, and leafy greens are your go-to. Y want to focus on heme iron (from animal sources) because it’s more efficiently absorbed. Non-heme iron (from plant foods) is still important but requires a bit more effort to absorb.

When do iron supplements actually make sense?

Iron supplements may be necessary, and certainly have their place!! For example, to help get out of a state of deficiency or anemia while underlying causes are addressed. Vegans and vegetarians as well as anyone with chronic medical conditions may need extra nutrient support. 

Here’s what to keep in mind:

• Supplement Forms: Iron supplements, especially ferrous sulfate, can irritate the digestive system, leading to nausea and constipation. If you suspect or have GI issues (constipation, diarrhea, bloating, reflux, have been told you have IBS or have IBD), chat with providers about a ferrous bisglycinate or iron chelate, which are gentler on the stomach and better absorbed.
• Monitoring & Dosage: Always monitor biofeedback and labs- especially ferritin levels to avoid iron overload and track progress. Ideally supplements wouldn’t be a long term solution. Taking iron with vitamin C can enhance absorption- which may or may not be beneficial. Take away from coffee/caffeine as it can inhibit uptake.

The bottom line

Iron deficiency is rarely a single-variable problem. Testing thoroughly, covering the partner nutrients, and addressing gut health and inflammation is key. Always dig deeper into that "why" . 

That's what a functional health approach is. If you're dealing with poor gut health, heavy periods, or suspect your liver needs support explore our guides to dig in further, or reach out about a 1-on-1 strategy session to thoroughly understand and work through your unique case and to build a plan around your body.

This article is for educational purposes and reflects a functional health perspective. It is not medical advice and does not replace individualized care from your physician. Always work with a qualified provider to interpret your labs and decide on supplementation.