4 Common Nutrient Deficiencies: Symptoms, Testing and How to Correct Them

You can eat a relatively healthy diet and still be at risk of a nutrient deficiency.

Low levels of nutrients such as iron, vitamin D, iodine and magnesium can occur for a variety of reasons, including inadequate dietary intake, restrictive diets, increased nutritional requirements, certain medications and conditions that affect digestion or nutrient absorption.

Some deficiencies can also develop without obvious symptoms at first.

When symptoms do occur, they can be surprisingly nonspecific. Fatigue, weakness, muscle cramps, poor concentration, changes in mood or reduced exercise tolerance can have many possible causes — including, in some cases, inadequate levels of essential nutrients.

That's why guessing based on symptoms alone isn't enough.

A combination of your diet, symptoms, medical history and appropriate blood tests can provide a much clearer picture of your nutritional status.

How Common Are Nutrient Deficiencies?

Nutrient deficiencies aren't equally common across every population, but some are particularly relevant in Australia.

Vitamin D deficiency

According to the latest Australian Bureau of Statistics data, 20.6% of Australian adults were vitamin D deficient in 2022–24. That's down from 23.8% in 2011–12, but vitamin D deficiency remains relatively common.

Vitamin D is important for calcium absorption, bone health, muscle function and normal immune function.

Your vitamin D status can be influenced by factors including sun exposure, skin pigmentation, age, location, lifestyle and how much time you spend outdoors.

Iodine deficiency

Iodine is required to produce thyroid hormones, which help regulate metabolism and support normal growth and development.

Australian Health Survey data from 2011–12 found that 18.3% of Australian women of childbearing age had iodine deficiency, based on urinary iodine concentration. The same survey found that nearly two-thirds had iodine levels below the level recommended for women who are pregnant, breastfeeding or considering pregnancy.

Iodine requirements are particularly important during pregnancy because thyroid hormones play an essential role in fetal development.

Magnesium

Magnesium is involved in hundreds of biochemical reactions throughout the body. It contributes to normal muscle and nerve function, energy production, bone health and the regulation of calcium and potassium transport across cell membranes.

Assessing magnesium status isn't always straightforward. Less than 1% of the body's magnesium is found in blood serum, and serum magnesium is tightly regulated. As a result, a normal serum magnesium result doesn't necessarily provide a complete picture of total magnesium stores or magnesium concentrations in tissues.

Iron deficiency

Iron deficiency is one of the most common nutritional deficiencies worldwide, particularly among women and people with increased iron requirements.

Iron is essential for haemoglobin production and oxygen transport. When iron stores become depleted, symptoms can include fatigue, weakness, reduced exercise tolerance, headaches and difficulty concentrating. More severe deficiency can lead to iron-deficiency anaemia.

Importantly, iron deficiency and iron-deficiency anaemia aren't exactly the same thing. You can have depleted iron stores before developing anaemia.

Why Do Nutrient Deficiencies Happen?

A deficiency isn't always caused by simply "not eating enough healthy food."

Potential contributors include:

• A restrictive or highly limited diet

• Vegetarian or vegan diets without careful nutritional planning

• Heavy menstrual bleeding

• Pregnancy or breastfeeding

• Increased athletic training

• Low overall food intake

• Gastrointestinal conditions

• Reduced nutrient absorption

• Certain medications

• Previous gastrointestinal surgery

• Increased nutritional requirements

This is why a personalised approach is more useful than simply taking a multivitamin and hoping for the best.

Why Iron Supplements Can Be Difficult to Tolerate

Iron supplements can be extremely useful when iron deficiency has been identified, but some people find oral iron difficult to tolerate.

Common side effects can include:

• Nausea

• Constipation

• Abdominal discomfort

• Diarrhoea

• A metallic taste

• Dark stools

The amount and type of iron, the formulation and how frequently it is taken can all affect tolerability.

If standard iron tablets cause significant gastrointestinal side effects, don't simply abandon treatment.

Speak with your GP or healthcare professional about whether a different formulation, dosing schedule or treatment approach may be appropriate.

For people with significant iron deficiency or those who cannot tolerate or absorb oral iron adequately, intravenous iron may sometimes be considered under medical supervision.

What About Liquid Iron?

Liquid iron can be an alternative for people who struggle to swallow tablets or don't tolerate a particular tablet formulation.

However, liquid iron isn't automatically better absorbed than every tablet formulation, and it can still cause gastrointestinal side effects.

The most appropriate form and dose depend on the individual, their iron levels and the reason for the deficiency.

If you have confirmed iron deficiency, the goal isn't simply to find the supplement with the best marketing claims.

It's to restore your iron status safely while identifying why your levels are low in the first place.

What About Iron Patches?

You may also see transdermal iron patches marketed as an alternative to oral iron supplements.

However, evidence supporting transdermal iron as an effective treatment for iron deficiency is limited. A patch shouldn't be assumed to provide the same amount of absorbable iron as a clinically appropriate oral or intravenous treatment.

If you have confirmed iron deficiency, use a treatment approach recommended by your doctor or appropriately qualified healthcare professional rather than relying on an unproven delivery method.

Magnesium: Does the Form Matter?

If you're considering magnesium supplementation, the type of magnesium can matter.

Research reviewed by the US National Institutes of Health indicates that the absorption of magnesium varies between different supplemental forms. Magnesium citrate, lactate, chloride and aspartate generally have greater bioavailability than magnesium oxide.

Magnesium citrate can also have a laxative effect, which may be useful for someone experiencing constipation but unpleasant for someone with sensitive digestion.

Magnesium glycinate is another popular supplement form, although claims that it is universally "the best absorbed" magnesium aren't supported strongly enough to make that a blanket recommendation.

More isn't necessarily better, either. The appropriate dose depends on your diet, health status, kidney function, medications and reason for supplementation.

What Should You Eat to Support Your Nutrient Levels?

Before reaching for supplements, look at your diet.

Iron-rich foods

Good sources include:

• Lean red meat

• Seafood and shellfish

• Eggs

• Lentils

• Beans

• Tofu

• Pumpkin seeds

• Dark leafy greens

If you follow a plant-based diet, combine plant sources of iron with vitamin C-rich foods such as capsicum, citrus fruit, berries or tomatoes to support non-haem iron absorption.

Vitamin D-rich foods

Dietary sources include:

• Oily fish such as salmon and sardines

• Egg yolks

• Fortified dairy products

• Fortified plant-based milks

However, food isn't the only source of vitamin D. Sun exposure is an important contributor to vitamin D status.

Iodine-rich foods

Sources include:

• Iodised salt

• Seafood

• Dairy products

• Eggs

Seaweed can contain very high and highly variable amounts of iodine, so more isn't necessarily better. Excessive iodine intake can also affect thyroid function.

Magnesium-rich foods

Include plenty of:

• Pumpkin seeds

• Almonds and other nuts

• Chia and other seeds

• Legumes

• Whole grains

• Spinach and other leafy greens

• Dark chocolate

A varied, minimally processed diet can provide a significant amount of magnesium without relying entirely on supplements.

Should You Take Supplements?

Not necessarily.

Supplements can be extremely useful when there is a confirmed deficiency, inadequate dietary intake or an increased nutritional requirement.

But taking multiple supplements "just in case" isn't always the best approach.

For example, taking high-dose iodine without a clear reason can be problematic for thyroid health, while excessive supplementation with certain nutrients can interfere with medications or cause adverse effects.

The goal should be targeted supplementation rather than supplementing everything.

How Do You Know If You're Deficient?

This is where testing can be helpful.

If you're experiencing unexplained fatigue, weakness, poor exercise tolerance, muscle symptoms or other persistent symptoms — or if your diet puts you at increased risk of nutritional deficiencies — speak with your GP about whether testing is appropriate.

Depending on your individual circumstances, your healthcare professional may consider tests relating to nutrients such as:

• Iron and ferritin

• Vitamin D

• Vitamin B12

• Folate

• Iodine

• Magnesium

The appropriate tests will depend on your symptoms, medical history and risk factors. Not every nutrient can be accurately assessed with a standard blood test, so testing should be individualised.

Don't Guess — Find Out What's Actually Missing

Feeling tired doesn't automatically mean you need iron.

Muscle cramps don't automatically mean you need magnesium.

And low energy doesn't automatically mean you have a vitamin D deficiency.

These symptoms can have many causes.

Instead of guessing, identify the potential nutritional gap first and then create a plan to address it.

A personalised nutrition approach can combine your symptoms, dietary intake, lifestyle and appropriate test results to determine where your diet may need support.

Once a deficiency has been identified, your nutrition and supplement strategy can be tailored to your individual needs and monitored over time.

Ready to Find Out What Your Body Needs?

If you suspect you may have a nutrient deficiency, we can help you identify potential nutritional gaps and work with your healthcare practitioner where appropriate to arrange testing.

From there, we can develop a personalised food and supplement plan designed around your individual results, dietary preferences and health goals.

The aim isn't to take every supplement on the shelf.

It's to give your body what it actually needs — and nothing it doesn't.