Vitamin Deficiency Test in London: Identify and Treat What Is Missing
Vitamin and mineral deficiencies are among the most common treatable causes of fatigue, brain fog, hair loss, low mood, and muscle weakness in the UK. The Online GP by The Wellness offers private vitamin deficiency blood testing at our Marylebone clinic with same-day appointments, results in 24 to 48 hours, and doctor interpretation that goes beyond simply flagging numbers as "normal" or "abnormal." Approximately 1 in 5 UK adults are deficient in vitamin D. Approximately 1 in 4 women of reproductive age are iron deficient. Vitamin B12 deficiency is increasingly common, particularly among vegetarians, vegans, and older adults. A single blood test can identify these deficiencies and others, and treatment is typically straightforward with rapid improvement in symptoms.
Book a Vitamin Test - WhatsApp | Email: team@thewellnesslondon.com | Call: 020 3951 3429
The Vitamins and Minerals That Matter Most
Not every vitamin needs testing. Your doctor will recommend a panel based on your symptoms, diet, lifestyle, and risk factors. Here are the deficiencies we investigate most frequently and why.
Vitamin D. The "sunshine vitamin" is essential for bone health, immune function, mood regulation, and muscle strength. The UK's northern latitude means that from October to March, sunlight is insufficient for the skin to produce adequate vitamin D. People who work indoors, cover their skin, have darker skin, or avoid sun exposure are at particular risk. Symptoms of deficiency include fatigue, muscle weakness, bone and joint pain, low mood, and increased susceptibility to infections. NICE recommends that all UK adults consider supplementation during autumn and winter, but the correct dose depends on your current level. A blood test provides this information.
Vitamin B12. Essential for nerve function, red blood cell production, DNA synthesis, and cognitive function. Deficiency causes fatigue, weakness, numbness or tingling in the hands and feet (peripheral neuropathy), a sore or unusually smooth tongue, mouth ulcers, cognitive difficulties, mood changes, and in severe cases, balance problems. B12 is found primarily in animal products, making vegetarians and vegans particularly vulnerable. Older adults are also at risk because stomach acid production (needed for B12 absorption) declines with age. Medications including metformin (for diabetes) and proton pump inhibitors (for acid reflux) can reduce B12 absorption.
Iron and ferritin. Iron is essential for haemoglobin production (carrying oxygen in the blood) and energy metabolism. Ferritin is the body's iron store. Crucially, ferritin can be depleted (causing fatigue, brain fog, hair loss, and reduced exercise tolerance) well before haemoglobin drops low enough to be classified as anaemia. This means your full blood count can look "normal" while your iron stores are dangerously low. Women of reproductive age are at highest risk due to menstrual blood loss. Heavy periods are the most common cause of iron deficiency in premenopausal women.
Folate (vitamin B9). Works alongside B12 in red blood cell production and DNA synthesis. Deficiency causes similar symptoms to B12 deficiency (fatigue, weakness, mouth ulcers) and is particularly important in women planning pregnancy, as adequate folate levels reduce the risk of neural tube defects. NICE recommends 400 micrograms of folic acid daily from before conception to week 12 of pregnancy.
Magnesium. Involved in over 300 enzymatic reactions in the body, including energy production, muscle contraction, nerve function, and sleep regulation. Deficiency causes muscle cramps, twitching, fatigue, difficulty sleeping, anxiety, and irregular heartbeat. It is common in people with high alcohol intake, diabetes, gastrointestinal conditions, and those on certain medications.
Zinc. Essential for immune function, wound healing, taste and smell, and skin health. Deficiency causes impaired immunity (frequent infections), slow wound healing, hair loss, skin problems, loss of taste or smell, and low mood. Common in vegetarians, vegans, and older adults.
Calcium. Essential for bone health, muscle function, nerve signalling, and blood clotting. Deficiency causes muscle cramps, numbness, tingling, and over time contributes to osteoporosis. Often tested alongside vitamin D, as the two work synergistically.
Who Should Get Tested
Anyone with persistent fatigue. Vitamin deficiency is one of the most common and most treatable causes. A comprehensive panel can identify the specific deficiency responsible.
Vegetarians and vegans. Plant-based diets can be nutritionally complete with proper planning, but B12, iron, zinc, and omega-3 levels should be monitored regularly. B12 supplementation is essential for vegans.
Women with heavy periods. Menstrual blood loss is the leading cause of iron deficiency in premenopausal women. If your periods are heavy, regular iron monitoring is important.
Pregnant women or those planning pregnancy. Folate, iron, vitamin D, and B12 are all critical for healthy pregnancy. Testing before conception allows deficiencies to be corrected in advance.
Older adults. B12 absorption declines with age. Vitamin D synthesis decreases. Calcium absorption reduces. Regular monitoring and supplementation can prevent deficiency-related complications.
People with darker skin tones. Higher melanin levels reduce vitamin D production from sunlight, increasing deficiency risk in the UK.
People taking medications that affect absorption. Metformin (B12), proton pump inhibitors (B12, magnesium, calcium), oral contraceptives (B6, folate), and others.
Anyone who wants a baseline. Even if you feel well, knowing your vitamin levels provides a reference point for the future and may identify early deficiencies before symptoms develop.
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Why Doctor Interpretation Changes Everything
The difference between a raw lab report and a doctor-interpreted result can be the difference between "your levels are fine" and "your levels explain exactly why you feel the way you do."
Laboratory reference ranges define the statistical normal range for the general population. They do not define the optimal range for you. A vitamin D level of 52 nmol/L is technically "sufficient" by UK guidelines but many people feel significantly better at levels above 75 nmol/L. A ferritin of 20 mcg/L is above the 15 mcg/L threshold for formal deficiency but is low enough to cause fatigue, hair loss, and brain fog in many women. A B12 of 200 pg/mL is within the normal range but is at the lower end, and some patients experience neurological symptoms at this level.
At The Online GP by The Wellness, your doctor does not just report whether your numbers fall within a reference range. They assess whether your levels are optimal for your age, sex, symptoms, and health goals. They consider the interaction between different nutrients (vitamin D and calcium, B12 and folate, iron and vitamin C). And they prescribe specific treatment: the right supplement, at the right dose, for the right duration, with a recheck scheduled to confirm improvement.
This is medical care, not a data service.
Discuss Your Results With a Doctor - WhatsApp | Email: team@thewellnesslondon.com | Call: 020 3951 3429
Frequently Asked Questions
What vitamins can you test? Vitamin D, B12, folate, iron/ferritin, magnesium, zinc, calcium, and other micronutrients based on your symptoms.
How much does it cost? Contact us for current pricing. All tests include doctor interpretation and consultation.
What are the symptoms of vitamin deficiency? Fatigue, hair loss, brain fog, muscle weakness, mood changes, numbness/tingling, frequent infections, mouth ulcers, and more. Symptoms overlap between deficiencies, making testing essential.
Do I need a referral? No. Book directly. A £49 phone consultation can help determine which tests are right for you.
How common is vitamin D deficiency? Approximately 1 in 5 UK adults. Higher in winter, in people with darker skin, and those who spend most time indoors.
Why is doctor interpretation important? Because "normal" on a lab report does not always mean "optimal for you." Your doctor assesses levels in clinical context and prescribes targeted treatment.
Can I get vitamin injections? B12 injections are available where clinically indicated. Your doctor will recommend the most appropriate supplementation route.
The Online GP by The Wellness provides private doctor-led healthcare from our Marylebone clinic. Contact us on WhatsApp at +44 7961 280835, email team@thewellnesslondon.com, or call 020 3951 3429.
References
NICE. Vitamin D deficiency in adults: treatment and prevention. Updated 2024.
NICE. Anaemia: iron deficiency. CKS. Updated 2025.
British Society for Haematology. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Updated 2024.
WHO. Iron deficiency anaemia: global prevalence. Updated 2024.
British Dietetic Association. Vitamin D and bone health. Updated 2025.
