Author: Kate Scott, DipNut, mBANT, rCNHC, mIFM | DNApal co-founder, clinical nutrition & genetics specialist

If you’ve ever had your thyroid tested and been told, “Everything looks normal,” yet you still feel exhausted, foggy and unlike yourself, you’re not alone.

Many people experience symptoms that strongly suggest thyroid dysfunction, despite being told their blood tests are within the normal range.

Perhaps you’re dealing with:

• Constant fatigue, even after a full night’s sleep.
• Weight gain or difficulty losing weight despite eating well.
• Hair thinning or loss of the outer third of the eyebrows.
• Puffiness around the face or eyes.
• Waking between 2am and 4am.
• Brain fog and poor concentration.
• Feeling cold when everyone else is comfortable.
• Morning headaches that disappear quickly.
• Constipation or sluggish digestion.
• Low mood and reduced motivation.

If this sounds familiar, it’s worth understanding that thyroid health is far more complex than a single blood test result.

Why “Normal” Thyroid Tests Don’t Always Tell the Full Story

The most commonly requested thyroid marker is Thyroid Stimulating Hormone (TSH).

TSH is produced by the pituitary gland and acts as a signal to the thyroid, telling it how much hormone to produce. While it provides useful information, it doesn’t tell us how effectively thyroid hormones are being activated and used throughout the body.

A more complete picture includes:

• TSH
• Free T4 (thyroxine)
• Free T3 (triiodothyronine)
• Thyroid antibodies (TPOAb and TgAb)
• Sometimes Reverse T3

T4 is the primary hormone produced by the thyroid gland, but it is largely inactive. Before it can influence metabolism, energy production, temperature regulation and cognitive function, it must be converted into T3, the biologically active thyroid hormone.

This conversion process is where many people run into problems.

The Critical Conversion Step: Turning T4 into T3

Approximately 80% of T4-to-T3 conversion occurs outside the thyroid gland, primarily in the liver, gut and peripheral tissues.

Several factors can impair this conversion, including:

• Chronic stress
• Inflammation
• Poor gut health
• Blood sugar instability
• Selenium deficiency
• Zinc deficiency
• Iron deficiency
• Chronic illness
• Excessive calorie or carbohydrate restriction

When conversion is impaired, you may experience many classic symptoms of hypothyroidism despite having a TSH result that falls within the laboratory reference range.

Your Genes Influence Thyroid Function

At DNApal, we analyse several genes involved in thyroid hormone production, regulation and activation. Our Thyroid DNA Report gives you a full picture of how your genes might be impacting you, what to look out for and how to support yourself.

DIO1 and DIO2: The Thyroid Activation Genes

The DIO1 and DIO2 genes encode deiodinase enzymes responsible for converting inactive T4 into active T3. Certain genetic variants may reduce the efficiency of this conversion process, meaning some individuals naturally produce less active thyroid hormone at tissue level. For these individuals, factors such as stress, inflammation and nutrient deficiencies may have an even greater impact on energy, metabolism and cognitive function.

PDE8B: Influencing TSH Levels

The PDE8B gene helps regulate thyroid signalling and is strongly associated with TSH levels. Research suggests that certain variants may predispose individuals to naturally higher TSH levels, potentially affecting how thyroid function appears on blood tests. This means that two people with identical thyroid hormone levels may have different TSH readings based partly on their genetics.

TSHR: The Thyroid’s Communication System

The TSHR gene encodes the receptor that receives the TSH signal from the pituitary gland. Variations in this gene may influence how sensitive the thyroid gland is to stimulation, potentially affecting hormone production and overall thyroid efficiency.

TRHR: The Brain-Thyroid Connection

The TRHR gene plays a role higher up in the hypothalamic-pituitary-thyroid (HPT) axis.

It helps regulate the signals that ultimately control thyroid hormone production. Genetic differences may influence the way the brain communicates with the thyroid gland, potentially contributing to variations in thyroid function between individuals.

Other Important Thyroid-Related Genes

Our Thyroid DNA Report also explores genes involved in:

• Autoimmune thyroid risk.
• Inflammation pathways.
• Nutrient requirements relevant to thyroid health.
• Hormone metabolism and detoxification.
• Stress resilience and cortisol regulation.

This helps explain why two people with similar blood test results can experience very different symptoms.

What Does “Optimal” Thyroid Function Look Like?

Reference ranges are designed to identify disease, not necessarily optimal health. For example, the upper limit of the TSH reference range often extends to around 4.5 mIU/L. However, many functional and integrative practitioners observe that people often feel their best when thyroid markers sit within a much narrower optimal range.

Rather than focusing on a single number, it’s important to consider:

• Symptoms
• TSH
• Free T4
• Free T3
• Antibodies
• Nutrient status
• Genetics
• Lifestyle factors

The goal is not simply to be “within range” but to support thyroid hormone production, conversion and cellular activity.

The Bottom Line

If you’re experiencing fatigue, weight gain, hair loss, brain fog, cold intolerance or other classic thyroid symptoms, don’t assume that a “normal” TSH result tells the whole story.

Thyroid health involves far more than a single blood marker. Hormone conversion, nutrient status, stress, gut health, inflammation and genetics all play important roles.

Understanding your unique genetic blueprint can provide valuable insight into how your thyroid functions and where personalised nutrition and lifestyle strategies may help support optimal health.

Because when it comes to your thyroid, “normal” isn’t always the same as optimal.

Want to take control of your health today? Visit our DNA packages to get started.