Vitamin D
Why nearly everyone in the UK is Vitamin D deficient in winter
The UK's latitude means UVB radiation is insufficient for synthesis between October and March. What the data shows about supplementation dose.
UK reference values · No supplements to sell
Know which nutrients you actually need
Most people self-prescribing supplements are either taking the wrong ones, the wrong dose, or ones that make no difference to their specific situation. The deficiency risk assessment gives you a clear picture based on your diet, lifestyle, and symptoms.
Sample Risk Profile
Vitamin D
High risk
Magnesium
Moderate
Vitamin B12
Moderate
Iron
Low risk
Omega-3
Moderate
Zinc
Low risk
Deficiency Risk Assessment
Eight questions about your diet, lifestyle, and symptoms. We score your risk for the six most commonly deficient nutrients in the UK — Vitamin D, B12, iron, magnesium, zinc, and omega-3.
Question 1 of 8
Your Risk Profile
Recommended actions
Supplement Guide
Evidence tiers for the most commonly discussed supplements in the UK — strong evidence, moderate evidence, or popular but weak. UK dosing guidelines used throughout.
Clarity over complexity
The UK supplement market is worth £500 million. Very little of it is necessary for people eating a varied diet.
UK reference values
We use SACN and NHS daily reference values, not US RDAs. Dosing context specific to the UK population and diet.
Evidence tiered clearly
Strong evidence, moderate evidence, or popular but weak — labelled on every supplement card so you can make an informed decision.
Food first, always
Where dietary sources can meet your needs, we say so before mentioning a supplement. Supplementation is a second option, not a default.
Symptom-based scoring
Fatigue, poor wound healing, frequent infections — each symptom pattern correlates with specific nutrient deficiencies in the clinical literature.
Diet type context
Vegan, vegetarian, pescatarian, and omnivore dietary patterns have different deficiency risk profiles — your assessment accounts for this.
No upsell, no conflict
No affiliate links, no recommended brands, no sponsored content. The tool earns trust by having no financial interest in your choices.
Nutrition science explained
Evidence-based guides that explain the research, not the marketing.
B12
B12 deficiency on a vegan diet: what the evidence says about dose and form
Cyanocobalamin vs methylcobalamin, daily vs weekly dosing, and why food fortification alone is rarely sufficient for fully plant-based diets.
Magnesium
Magnesium: the nutrient most people are slightly short of without knowing it
UK population surveys show mean intake below reference values. Why it matters for sleep, muscle function, and stress response — and which form is best absorbed.
Common questions
For most supplements, it is not essential before starting at maintenance doses. Vitamin D at 1,000–2,000 IU daily is safe for essentially all adults without testing. However, iron is an exception — excess iron is harmful, and iron supplementation should only begin if a serum ferritin test confirms deficiency. B12 testing is useful if you have been symptomatic for more than a few months.
Completely free. No account, no email address, no subscription. The entire assessment runs in your browser. Deficiency Lab has no financial relationship with any supplement brand, and we do not earn commission on any products mentioned.
It is a structured risk assessment, not a clinical test. The scoring model is based on well-established risk factors in the literature — vegan diet predicts B12 risk, UK latitude predicts Vitamin D risk, low red meat and menstruation predict iron risk. It gives you a well-reasoned starting point. It does not replace blood testing or a dietitian consultation.
For most people eating a varied diet, no. The evidence for multivitamins reducing disease risk or improving outcomes in healthy, well-nourished adults is weak. A better approach is identifying specific deficiency risks — which this tool helps with — and addressing only those. The exception is Vitamin D, which the UK government recommends everyone supplement October to March regardless of diet.
B12 is the only nutrient that cannot be obtained reliably from a well-planned plant-based diet — it is strongly recommended for all vegans. Vitamin D supplementation is recommended for the UK population generally. Iodine is often overlooked: it is primarily obtained from dairy and fish in omnivore diets, and is deficient in many plant milks. Omega-3 as algae-based DHA/EPA is worth considering if you do not eat fish.
Yes, for several nutrients. Fat-soluble vitamins (A, D, E, K) accumulate and can cause toxicity at high doses. Iron excess is toxic and correlated with increased oxidative stress. Zinc at high doses suppresses copper absorption. Water-soluble vitamins like B and C are largely excreted at excess, but B6 causes peripheral neuropathy at sustained high doses. Stick to maintenance-level supplementation unless directed by a clinician.
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