Iron Deficiency, Ferritin and Iron Supplements: How to Understand Your Iron Status

Written by Dr. Megan Woroch, ND
Naturopathic Doctor in Toronto, Ontario
Published: July 19, 2026 · Updated: September 21, 2026

Iron deficiency is one of the most common nutrient deficiencies, and it can affect how you feel, exercise, think and function long before anemia develops.

Importantly, iron deficiency isn't always as simple as low hemoglobin. You can have depleted iron stores while your hemoglobin is still within the normal range. That is why ferritin, CBC, and a full iron panel can give a much more complete picture of your iron status.

If you have been told that your iron is “normal” but you are still experiencing fatigue, reduced exercise tolerance, hair shedding, brain fog or other symptoms, it may be worth looking more closely at the full picture.

What are the symptoms of iron deficiency?

Iron is essential for oxygen transport, energy production, neurotransmitter function and many other processes throughout the body. As iron stores deplete, symptoms can develop before anemia.

Possible symptoms of iron deficiency include:

• Fatigue or low energy

• Reduced exercise tolerance or endurance

• Feeling weak or easily exhausted

• Brain fog or difficulty concentrating

• Headaches or dizziness

• Feeling unusually cold

• Shortness of breath with exertion

• Heart palpitations or a racing heart

• Hair shedding or thinning

• Brittle or ridged nails

• Restless legs

• Irritability or changes in mood

• Decreased physical performance or slower recovery

As iron deficiency progresses to iron-deficiency anemia, symptoms can become more pronounced and may include significant fatigue, weakness, shortness of breath, dizziness, headaches, palpitations, difficulty concentrating and, in more significant cases, chest discomfort.

These symptoms are not specific to iron deficiency and can have many other causes. Blood work is therefore important to determine whether low iron is actually contributing to how you feel.

What ferritin level is considered low in Ontario?

Ferritin is one of the most useful blood markers for assessing iron stores.

In September 2024, Ontario laboratories changed how ferritin results are reported. Instead of a traditional reference interval, labs now use clinical decision limits to help identify iron deficiency.

For adults:

• Ferritin <30 µg/L: consistent with iron deficiency

• Ferritin 30–50 µg/L: probable iron deficiency

• Ferritin 51–100 µg/L: possible iron deficiency when risk factors are present

• Ferritin 101–300 µg/L: iron deficiency is unlikely

• Ferritin ≥600 µg/L: consider evaluation for iron overload

These ranges are most useful when there is no significant inflammation. Ferritin is also an acute-phase reactant, meaning inflammation or infection can increase ferritin and potentially mask underlying iron deficiency. When inflammation is present, other iron studies, including transferrin saturation and TIBC, become particularly important.

It is also important not to interpret ferritin in isolation. A ferritin of 45, for example, may mean something different depending on the person's symptoms, menstrual history, diet, inflammation, exercise demands and other laboratory findings.

Can you be iron deficient if your hemoglobin is normal?

Yes.

Iron deficiency often develops in stages. The body initially depletes its iron stores before it significantly affects red blood cell production and hemoglobin.

This means someone can have:

Low iron stores → iron-deficient red blood cell production → iron-deficiency anemia

A normal hemoglobin therefore does not necessarily mean that iron stores are optimal.

This distinction can be particularly relevant for people experiencing fatigue, hair shedding, restless legs or reduced exercise performance who have been told that their CBC is “normal.”

Which blood tests should you check for iron deficiency?

Rather than looking at one number, I prefer to consider the broader pattern.

Ferritin

Ferritin provides information about stored iron.

It is useful for identifying depleted iron stores, but remember that inflammation can artificially increase ferritin.

Serum iron

Serum iron measures the amount of iron circulating in the blood at the time of testing.

It can fluctuate throughout the day and with recent food or supplement intake, so serum iron alone is not a particularly reliable way to determine whether someone is iron deficient.

TIBC and transferrin

These provide information about the body's capacity to transport and bind iron.

Transferrin saturation

Transferrin saturation, often abbreviated TSAT, indicates how much of the available iron-binding capacity is occupied by iron.

It can be particularly helpful when inflammation may affect ferritin.

CBC

A complete blood count provides information about red blood cells and whether iron deficiency has progressed to anemia.

Useful markers include:

• Hemoglobin

• Hematocrit

• RBC count

• MCV

• MCH

• MCHC

• RDW

This is why a full iron assessment is often more informative than simply checking “iron.”

What is the best iron supplement?

There is no single iron supplement that is best for everyone.

Different forms of iron vary in elemental iron content, absorption, tolerability and cost. The right choice depends on the degree of deficiency, whether anemia is present, digestive tolerance and how well someone responds.

Ferrous sulfate, fumarate and gluconate

These are traditional forms of non-heme iron and are commonly used because they are inexpensive and effective.

The downside is that they can cause gastrointestinal side effects, particularly at higher doses.

Ferrous bisglycinate

Iron bisglycinate is iron bound to the amino acid glycine.

It is often well tolerated and can be a useful option for people who experience constipation, nausea or abdominal discomfort with traditional iron salts.

Heme iron

Heme iron is derived from animal sources and is absorbed through a different pathway than non-heme iron.

Its absorption is less affected by some dietary inhibitors, and some people may tolerate it better. However, it is not automatically the best option for everyone.

Liposomal and sucrosomial iron

These newer forms are designed to alter how iron is delivered through the gastrointestinal tract, with the goal of improving absorption and/or tolerability.

Some people tolerate these forms very well, but the evidence base is not as extensive as it is for traditional iron preparations. A higher price tag also does not necessarily mean better results.

Don't forget about elemental iron

One of the most confusing parts of choosing an iron supplement is that the amount listed on the front of the bottle may not represent the amount of elemental iron.

Different iron compounds contain different percentages of elemental iron. When comparing supplements, look at the elemental iron dose rather than the total milligrams of the iron compound.

More iron is also not necessarily better. Higher doses can increase side effects and, because of the body's iron-regulating mechanisms, may not proportionally increase absorption.

Why does iron cause constipation and stomach upset?

Gastrointestinal side effects are one of the biggest reasons people stop taking iron.

Common side effects include:

• Constipation

• Nausea

• Abdominal discomfort

• Bloating

• Changes in bowel movements

• Dark or black stools

If this happens, the answer is not necessarily to stop iron altogether.

Depending on the situation, it may be possible to improve tolerance by:

• Using a different form of iron

• Reducing the dose

• Taking iron less frequently

• Using alternate-day dosing

• Taking iron with a small amount of food if necessary

Taking iron with food may reduce absorption somewhat, but a supplement you can take consistently is often more useful than one that is theoretically better absorbed but impossible to take regularly.

What is hepcidin, and What is its role?

Hepcidin is one of the body's primary regulators of iron absorption and iron availability.

You can think of hepcidin as a brake on iron absorption.

When hepcidin levels increase, the intestine absorbs less iron and less stored iron is released into circulation.

Interestingly, taking oral iron itself can temporarily increase hepcidin. Research has shown that larger doses can produce a hepcidin response that reduces the fractional absorption of subsequent doses.

This is one reason why taking increasingly large doses of iron, or taking iron multiple times throughout the day, does not necessarily translate into proportionally more iron being absorbed.

Is alternate-day iron better?

For some people, yes.

Research has found that taking oral iron on alternate days can increase fractional iron absorption compared with taking the same dose on consecutive days. It may also reduce gastrointestinal side effects for some people.

However, alternate-day dosing is not automatically appropriate for everyone.

The ideal schedule depends on:

• How low the iron stores are

• Whether anemia is present

• How much elemental iron is being taken

• How quickly iron needs to be replaced

• Gastrointestinal tolerance

• The underlying cause of the deficiency

For uncomplicated iron deficiency, alternate-day dosing can be a useful strategy to discuss with your healthcare provider. More significant anemia may require a different approach.

Can exercise affect iron absorption?

Exercise is another reason iron status can be complicated, particularly for people who train frequently or participate in endurance sports.

Strenuous or prolonged exercise can temporarily increase hepcidin, with levels often peaking approximately 3–6 hours after exercise. This can reduce the amount of iron absorbed from food or supplements during that window.

Athletes may also have additional contributors to iron depletion, including increased iron requirements, dietary restriction, sweat losses and, in some cases, gastrointestinal or urinary losses.

This does not mean you should avoid exercise or automatically avoid taking iron after every workout. Rather, for someone with low iron who trains regularly, the timing of exercise, meals, and iron supplementation may be worth considering as part of the bigger picture.

Should you take vitamin C with iron?

Vitamin C can enhance the absorption of non-heme iron, which is why taking iron with vitamin C or a vitamin-C-rich food has traditionally been recommended.

For many people, you don't need to add a separate vitamin C supplement. Taking iron with water and including vitamin C-rich foods in the diet is a reasonable approach.

What about B vitamins?

B vitamins and iron have different roles.

Vitamin B12 and folate are important for healthy red blood cell production, while other B vitamins support energy metabolism and many cellular processes.

If fatigue or anemia is present, it can therefore be useful to consider whether B12, folate or other nutrient deficiencies may also be contributing.

But B vitamins do not need to be routinely taken alongside iron simply to make iron absorb better. Supplementation should be based on dietary intake, blood work and individual needs.

What should you avoid taking with iron?

Several foods and supplements can interfere with non-heme iron absorption.

These include:

• Coffee

• Tea

• Calcium

• Some other mineral supplements

• Certain medications, depending on the medication and formulation

Coffee and tea are particularly relevant because their polyphenols can significantly reduce non-heme iron absorption.

When possible, I generally recommend taking iron at least 4 hours away from coffee, tea, calcium and other mineral supplements.

Should iron be taken on an empty stomach?

Iron is generally absorbed better away from food, but this has to be balanced against tolerability.

For someone who can tolerate iron on an empty stomach, taking it with water between meals may maximize absorption.

For someone who becomes nauseated or constipated, taking it with a small amount of food may be a reasonable compromise.

There is no benefit to having a perfect iron schedule if the person cannot tolerate the supplement consistently.

What if your ferritin isn't increasing?

If someone consistently takes iron and their iron status isn’t improving, simply increasing the dose may not be the best next step.

It is worth asking why the iron isn't being absorbed, retained or replenished.

Potential considerations include:

1. Is enough iron actually being absorbed?

Digestive and gastrointestinal factors can affect iron absorption, including:

• Celiac disease

• Inflammatory bowel disease

• H. pylori infection

• Changes in stomach acid

• Certain acid-suppressing medications

• Other gastrointestinal conditions

Digestive symptoms are not required for an absorption issue to be present.

2. Is there ongoing blood loss?

Ongoing blood loss is an important cause of iron deficiency.

For people who menstruate, heavy menstrual bleeding can be a significant contributor.

Depending on age, sex, symptoms and individual risk factors, gastrointestinal blood loss may also need to be considered.

Other contributors can include frequent blood donation or, in some athletes, exercise-related losses.

If iron deficiency keeps recurring despite supplementation, identifying and addressing the source of the loss is essential.

3. Is inflammation affecting iron metabolism?

Inflammation can increase hepcidin and alter how the body absorbs iron and releases it from storage.

It can also make ferritin more difficult to interpret because ferritin itself rises during inflammation.

This is one reason it's important to look at ferritin alongside the broader iron panel and clinical picture.

4. Is the dose or schedule appropriate?

More iron is not always better.

The form, elemental iron dose, timing, frequency, and individual tolerance can all influence how much iron is actually absorbed.

How quickly should iron levels improve?

The timeline depends on the severity and cause of the deficiency, whether anemia is present, the type and dose of iron being used and how well it is absorbed.

Hemoglobin may improve before iron stores are fully replenished, so treatment often needs to continue beyond the point at which someone starts feeling better.

Follow-up blood work can help determine whether the treatment is working and whether iron stores are actually being restored.

If ferritin or hemoglobin is not responding as expected, that is useful information. It may indicate a need to reassess the dose, adherence, absorption, ongoing blood loss or another underlying contributor.

The bottom line

Iron deficiency is about more than just hemoglobin.

Someone can have depleted iron stores while their CBC still looks normal, and symptoms such as fatigue, brain fog, hair shedding, restless legs or reduced exercise tolerance may warrant a closer look at iron status.

A comprehensive assessment can include:

Ferritin → iron storage
Serum iron + transferrin/TIBC + transferrin saturation → iron availability and transport
CBC → impact on red blood cell production
Clinical context → diet, menstrual or other blood loss, inflammation, digestion, medications and exercise

When supplementation is needed, no single “best” form of iron fits everyone. Individualize the form, dose, timing, and frequency based on the person's needs and tolerance.

And perhaps most importantly, if iron deficiency persists or keeps coming back, the goal shouldn't be simply to keep taking more iron. Understanding why the deficiency developed in the first place is an important part of long-term management.

Dr. Megan Woroch, ND, is a Toronto-based naturopathic doctor with a focus on digestive health, immune and environmental health, and root-cause approaches to chronic health concerns. She uses evidence-informed naturopathic medicine, clinical nutrition, functional testing, and individualized supplementation to support her patients.

Disclaimer: This information is for educational purposes only and is not intended to provide or replace medical advice, diagnosis, or treatment. Always consult your qualified healthcare provider for individualized recommendations.