Mental Health Is Multifactorial – But Biology Still Counts

When Low Mood Isn’t “Just in Your Head”: How Physical Health Can Drive Mental Health Symptoms

Living with low mood, anxiety, or persistent brain fog is hard enough. It’s worse when you get told things like:

“It’s just stress.”
“It’s just depression.”
“Your bloods are normal.”

You walk out thinking: If it’s all just in my mind, why does my whole body feel wrong?

Mental health is never “just one thing”. Life events, relationships, work, finances, trauma, sleep, personality, neurodiversity – all of it matters. But there’s a major piece that is often under-checked:

Physical (organic) health problems can directly drive or worsen mental health symptoms.

That doesn’t mean your feelings aren’t real. It means your brain is part of your body. If the body is off, mood, anxiety, and thinking often go with it.

Mental Health Is Multifactorial – But Biology Still Counts

Most people intuitively understand the psychological and social side of mental health:

• Life stresses: relationship conflict, work pressure, money worries, caring responsibilities, bereavement.
• Past experiences: childhood adversity, trauma, long-term stress.
• Lifestyle: poor sleep, inactivity, heavy alcohol use, recreational drugs.
• Neurodiversity: ADHD, autism and others – often linked with higher anxiety and depression, especially in an unsympathetic environment.
• Primary psychiatric illness: bipolar disorder, schizophrenia, schizoaffective disorder, OCD, etc.

All of these are real and important. But there is another layer

• Organic (physical) conditions that affect brain chemistry and nervous system function.

Modern guidance on depression – including NICE – explicitly reminds clinicians to consider physical causes such as anaemia, thyroid disease, and B12 deficiency when assessing low mood. That’s not “functional medicine”; that’s baseline good practice.

When Should You Be Especially Suspicious of an Organic Cause?

You cannot diagnose yourself from a blog. But some patterns should make any GP think about biology more seriously.

1. Minimal or No Psychosocial Stressors

You feel:

• Low, flat, or emotionally “numb”, or
• Highly anxious, restless, or on edge

…but:

• No major relationship or work crisis
• No recent bereavement or big life shock
• No obvious external trigger

That doesn’t prove a physical cause, but it raises the odds that organic factors (hormones, deficiencies, metabolic issues) are contributing.

2. Intrusive or Obsessive Thoughts With Sudden or Severe Onset

Intrusive or obsessive thoughts can occur in primary psychiatric conditions too – OCD, mood disorders, psychosis and others. The point is not to claim they’re always organic.

The key is change and context:

• The thoughts are new or clearly out of character, and
• They appear relatively suddenly, and
• They sit alongside new physical symptoms such as:
  
  • Marked fatigue
  • Neurological changes (tingling, clumsiness, imbalance)
  • Palpitations
  • Weight change
  • Temperature intolerance, sweats
  • Bowel or menstrual changes

In that situation, it is reasonable to think about organic contributors as well as psychiatric causes. Not instead of – as well as.

3. Ongoing Physical Symptoms Alongside Mood Symptoms

You have low mood, anxiety, or brain fog and:

• Breathlessness or palpitations
• Dizziness or feeling “faint”
• Unexplained weight loss or gain
• Changes in bowel habit
• Hair loss or dry, thinning hair
• Feeling cold when others are fine
• Muscle weakness or aches
• Pins and needles / numbness in hands or feet
• Headaches that are new or changing

Again: no single symptom proves anything. But taken together, they’re strong justification for checking your physical health properly, not just assuming “it’s all psychological”.

Common Physical Causes That Can Affect Mood and Thinking

Here are some of the key organic contributors that can feed directly into mental health.

1. Low Vitamin B12

B12 is essential for:Nerve function

• Red blood cell production
• DNA synthesis
• Several pathways involved in brain chemistry

Mental symptoms can include:

• Fatigue and low energy
• Brain fog, poor concentration
• Irritability
• Low mood and anxiety
• In more severe cases: cognitive changes, personality change, even psychosis-like symptoms

Physical clues can include:

• Numbness or tingling in hands/feet
• Balance problems or clumsiness
• A sore tongue, mouth ulcers
• Pale skin
• Sometimes bowel changes

Someone with significant B12 deficiency may be labelled “depressed and anxious” while their nervous system is literally starved of a key vitamin.

2. Low Iron / Iron Deficiency (With or Without Anaemia

You can have iron deficiency with normal haemoglobin. That’s often missed.

Mental symptoms:

• Marked tiredness
• Brain fog
• Poor motivation
• Irritability
• Heightened anxiety or a sense of inner restlessness

Physical clues:

• Shortness of breath on exertion
• Palpitations
• Restless legs
• Headaches
• Heavy periods
• Pale skin
• Hair loss

If only haemoglobin is checked and nobody looks at ferritin or iron studies, this is very easy to overlook.

3. Thyroid Problems

Your thyroid hormones are your metabolic “volume knob”.

• Hypothyroidism (underactive thyroid) can cause:
  
  • Low mood, apathy
  • Fatigue and sleepiness
  • Weight gain
  • Slowed thinking and memory problems
  • Constipation
  • Feeling cold, dry skin, hair loss
• Hyperthyroidism (overactive thyroid) can cause:
  
  • Anxiety, agitation, irritability
  • Palpitations and tremor
  • Heat intolerance and sweating
  • Weight loss despite normal or increased appetite
  • Sleep disturbance

In both cases, the mental health symptoms can be prominent enough that the thyroid issue is missed if nobody checks.

4. Vitamin D Deficiency

Vitamin D is involved in:

• Bone metabolism
• Immune function
• A range of signalling pathways, including some affecting the brain

Evidence suggests an association between low vitamin D and:

• Low mood
• Fatigue
• Generalised aches and pains

It is rarely the sole cause of depression, but severe deficiency can drag overall resilience and mood down.

5. Calcium and Parathyroid Disorders

Calcium that is significantly too high or too low can affect:

• Mood
• Irritability
• Concentration and memory
• In more severe cases, confusion or agitation

The parathyroid glands regulate calcium. When they’re over- or underactive, you can see a mixture of:

• Bone pain
• Abdominal discomfort
• Kidney stones (with high calcium)
• Muscle cramps and tingling (with low calcium)
• Low mood, anxiety, or cognitive slowing

6. Blood Sugar, Sleep, Inflammation and More

Other important contributors include:

• Blood sugar dysregulation
  • Hypoglycaemia and poorly controlled diabetes can cause irritability, fatigue, and “brain crashes”.
• Chronic inflammation and infection
  
  • The immune system and brain talk constantly. Long-term inflammation can sap energy and flatten mood.
• Obstructive sleep apnoea
  
  • Night-time breathing pauses, low oxygen, and fragmented sleep → daytime exhaustion, poor focus, low mood, and irritability.
• Medication side-effects
  
  • Steroids, some blood pressure drugs, hormonal treatments, and others can significantly affect mood and anxiety.
     

The point isn’t that every case of depression or anxiety is “just a deficiency” or “just thyroid”. The point is that if you never look, you will miss people whose symptoms are at least partly reversible.

How Can You Tell If There Might Be a Physical Element?

You can’t self-diagnose from this list. But you can decide that further assessment is reasonable.

Ask yourself:

• Do I have persistent physical symptoms along with my mental health symptoms?
• Are my symptoms out of proportion to the stresses in my life?
• Did my intrusive or obsessive thoughts or personality changes appear fairly suddenly, and do they feel unlike me?
• Have I actually had a full physical check and appropriate blood tests, or just a quick “Your bloods are normal” with no details?

If the answer to several of those is “yes”, your next step isn’t to panic – it’s to have a more structured conversation with a doctor.

What a Thoughtful Physical Screen Might Include

This is not a rigid shopping list; tests should always be guided by your story. But commonly a GP might reasonably consider:

• Full blood count (FBC) – anaemia, infection clues
• Iron studies / ferritin – iron stores, not just Hb
• Vitamin B12 and folate
• Thyroid function tests (TSH ± T4/T3)
• Vitamin D (in many UK patients)
• Urea & electrolytes / kidney function
• Liver function tests
• Glucose and/or HbA1c – for blood sugar/diabetes
• Calcium, and in some cases parathyroid hormone
• Inflammatory markers if there is suspicion of inflammatory or autoimmune disease

Normal results are still valuable – they rule things out. Abnormal results don’t automatically mean “this is the whole story”, but they give you concrete targets to address.

Mind and Body, Not Mind or Body

Two equally unhelpful extremes:

• “It’s all in your head. Therapy and antidepressants only.”
• “It’s all deficiencies and hormones. Therapy is pointless.”

Reality:

• Psychological therapies, social support, lifestyle change, and sometimes medication are crucial.
• Organic factors like B12, iron, thyroid, vitamin D, calcium, blood sugar, sleep, and inflammation can significantly influence how well those other treatments work – and sometimes are key drivers themselves.

The aim of checking organic causes is not to replace therapy or meds; it’s to stop you fighting your brain with one hand tied behind your back.

What You Can Do If This Resonates

Practical steps, not grand gestures:

1. Write everything down
   
   • Mood, anxiety, intrusive/obsessive thoughts, sleep, concentration.
   • Physical symptoms: breathlessness, palpitations, dizziness, weight change, bowel change, periods, hair/skin changes, numbness, headaches.
   • When things started, and how they’ve changed.
2. Find out what’s already been checked
   
   • Ask your GP (or check your online records if available):
     
     • Which blood tests have you had in the last 1–2 years?
     • Were B12, iron/ferritin, thyroid, vitamin D, glucose, calcium included?
   • Were any results borderline or low-normal and just not commented on?
3. Have a specific conversation
   For example:
   “I know life stress is part of my mental health, but I’m also worried about possible physical contributors like B12, iron, thyroid or vitamin D. Could we review my physical health more systematically?”
4. Don’t DIY yourself into trouble
   
   • Avoid high-dose supplements, hormones, or abrupt stopping of psychiatric medication without medical advice.
   • Use your curiosity to get better assessment, not to replace it.
5. Know when it’s urgent
   Whatever the cause, you need urgent assessment (GP same day, NHS 111, or A&E depending on intensity) if you have:
   
   • Suicidal thoughts with intent or plans
   • Hallucinations or delusions
   • Severe agitation, confusion, or sudden major behaviour change
   • Suspected overdose or dangerous self-harm

Organic and psychiatric causes can overlap. Both need respect.

A Calm Next Step

If you’ve been living with low mood, anxiety, intrusive thoughts or brain fog, especially if:

• You don’t have obvious major psychosocial stressors, and/or
• You have clear physical symptoms at the same time,

then it’s reasonable to ask whether your physical health has been properly explored, or just briefly glanced at.

A GP with an interest in metabolic and organic contributors to mental health at Rubicon Private Health can review your symptoms, history and blood tests in a structured way. Not as a magic fix, but as part of a joined-up plan that treats your mind and body as one system.

Disclaimer

This article is for general information only. It is not a diagnosis and not a substitute for a consultation with your own GP or mental health professional. If you are experiencing suicidal thoughts, hallucinations, severe agitation, or sudden major changes in behaviour, seek urgent medical attention via your GP, NHS 111, or A&E.