Do GLP-1s Cause Iron Deficiency?

Can GLP-1s cause iron deficiency?

Research shows people on GLP-1s are more likely to be iron deficient. But this isn't a direct effect of the treatment. Instead, the way they work and affect your metabolism may reduce your body's ability to absorb iron.

In this guide, we’ll go through ways GLP-1s may indirectly lead to low iron levels, symptoms of iron deficiency, and how to prevent it.

Medically reviewed by

Sanjeda Chowdhury, Superintendent Pharmacist + Independent Prescriber

Delayed gastric emptying

Delayed gastric emptying is one mechanism by which GLP-1 receptor agonists help you feel fuller, as food remains in the stomach for longer. This often leads to reduced appetite and lower overall food intake, which can reduce dietary iron consumption. Less iron consumption = less overall iron absorption.

Iron is primarily absorbed in the small intestine. But before this can happen, it needs to be released from food and converted into a more absorbable form by digestion in the stomach.

When food and bacteria sit in the stomach for longer, it allows bacteria to multiply in the intestine. This potentially increases the risk of small intestinal bacterial overgrowth (SIBO), a condition where excessive bacteria accumulate in the small intestine. SIBO may impair the absorption of nutrients, including iron, as bacteria compete for available nutrients and the associated inflammation can reduce the intestine's absorptive capacity.

Appetite suppression

GLP-1 medications reduce appetite, which helps you eat less. While this is effective as a weight loss strategy, it can also mean you get less nutrients from your diet.

It can also lower your enjoyment of rich foods like steak or lamb, which are high in iron. Side effects like nausea can create food aversions, making foods with strong flavours, textures or appearances unappealing. For example, steak may be perceived as too meaty, or spinach as too green. This change in diet and reduction in food intake can result in many people who used to eat enough iron no longer doing so.

Inflammation in the body

GLP-1 medicines generally reduce inflammation and often improve liver health. But in rare cases, they can indirectly contribute to liver problems.

GLP-1 medicines slow stomach emptying and may reduce gallbladder emptying. When combined with rapid weight loss, this can increase the risk of gallstone formation. If a gallstone blocks your bile ducts, bile can’t drain properly, which can lead to cholestasis (a condition where bile flow is blocked) and liver inflammation. Because the liver plays an important role in iron regulation and storage, impaired liver function can affect your body's iron balance.

You’re more likely to experience liver problems if you have certain underlying conditions, lose weight too quickly, or have other risk factors. But even then, it’s still quite rare.

Symptom	Why?	Can be mistaken for:
Fatigue	Without enough iron, your body can’t make haemoglobin, the protein that carries oxygen around your body. As less oxygen reaches the tissues and muscles, it can cause fatigue and weakness.	Reduced calorie intake from GLP-1s can cause fatigue.
Hair thinning	Iron is essential for healthy hair growth. Low levels of it can deprive your hair of essential nutrients and oxygen, causing your hair to thin.	Significant weight loss can cause temporary hair loss known as telogen effluvium.
Shortness of breath	Low haemoglobin levels force your heart and lungs to work harder to send enough oxygen to your muscles.	People who didn’t previously maintain a regular fitness routine may find that managing increased physical activity becomes more challenging while using GLP-1 medicines.
Feeling cold	Lack of iron reduces your body’s ability to produce heat, making you feel constantly cold.	Fat acts as a natural insulator. As you lose excess fat, you might feel colder.
Heart palpitations	When haemoglobin is low, the heart may beat faster or harder to deliver enough oxygen around the body, which can cause palpitations.	A fast heart rate is a rare side effect of GLP-1 medicines. Dehydration caused by nausea and vomiting can lead to an electrolyte imbalance, which may increase heart rate.

Symptom

Why?

Can be mistaken for:

Fatigue

Without enough iron, your body can’t make haemoglobin, the protein that carries oxygen around your body. As less oxygen reaches the tissues and muscles, it can cause fatigue and weakness.

Reduced calorie intake from GLP-1s can cause fatigue.

Hair thinning

Iron is essential for healthy hair growth. Low levels of it can deprive your hair of essential nutrients and oxygen, causing your hair to thin.

Significant weight loss can cause temporary hair loss known as telogen effluvium.

Shortness of breath

Low haemoglobin levels force your heart and lungs to work harder to send enough oxygen to your muscles.

People who didn’t previously maintain a regular fitness routine may find that managing increased physical activity becomes more challenging while using GLP-1 medicines.

Feeling cold

Lack of iron reduces your body’s ability to produce heat, making you feel constantly cold.

Fat acts as a natural insulator. As you lose excess fat, you might feel colder.

Heart palpitations

When haemoglobin is low, the heart may beat faster or harder to deliver enough oxygen around the body, which can cause palpitations.

A fast heart rate is a rare side effect of GLP-1 medicines. Dehydration caused by nausea and vomiting can lead to an electrolyte imbalance, which may increase heart rate.