Why more vitamins, antioxidants, and probiotics don’t always mean better health, and how precision nutrition could change how we prescribe supplements.
When the prescription becomes part of the problem
Imagine entering a pharmacy carrying a shopping basket filled with medicines, vitamins, minerals, probiotics, fish oils, herbal extracts and antioxidants.
Every item has a purpose. Every product promises a benefit. Yet nobody has checked whether all these substances are necessary, whether they interact, or whether the body can safely handle them together.
Could the very supplements intended to improve health sometimes become another source of illness?
This question occupied my thoughts after two encounters this week.
The first was with a lady living with diabetes, hypertension, high cholesterol, vasculitis, chronic constipation, adrenal insufficiency and mast cell activation syndrome. She was taking numerous prescribed medications alongside an extensive collection of supplements.
My immediate concern was that she might have several nutritional deficiencies, perhaps requiring antioxidant support or correction of specific hormonal and metabolic problems.
But another question soon emerged: would adding even more supplements genuinely help her?
The second encounter was a conversation with a professor interested in metabolic health, recently returned to London after delivering his annual lecture in India. We discussed precision medicine, polypharmacy and the growing interest in personalised supplementation.
These conversations highlighted a paradox.
Modern medicine increasingly recognises the dangers of inappropriate polypharmacy. Yet nutritional medicine sometimes responds to complex illness by adding more supplements.
Perhaps we need to reconsider that approach.
From polypharmacy to poly supplementation
Polypharmacy refers to the use of multiple medicines, often necessary when someone has several chronic conditions.
It is not automatically harmful. A person with diabetes, hypertension and adrenal insufficiency may require several essential medicines, each serving a different purpose.
The problem arises when treatment becomes poorly coordinated, unnecessarily complicated or potentially harmful.
The same principle applies to supplements.
Consider someone taking a multivitamin, B-complex, magnesium, vitamin D, zinc, fish oil, turmeric, probiotics and several antioxidant formulations.
Some may be beneficial. Others may duplicate nutrients already present in the multivitamin. Some could interact with medication.
For example, certain herbal preparations can alter drug metabolism, high-dose vitamin E may increase bleeding concerns, and excessive vitamin B6 can damage peripheral nerves.
The NHS advises against taking more than 10 mg of supplemental vitamin B6 daily without medical advice. [1]
A 2026 update from the NHS Specialist Pharmacy Service reinforces the importance of person-centred medication reviews, particularly in people managing multiple conditions.
We should apply the same discipline to nutritional prescriptions.
The question is not how many supplements a person takes, but how many they actually need.
The body is a sophisticated chemical factory, not an unlimited storage warehouse
Imagine the human body as a large factory.
The gut is the receiving department. The liver processes and transforms many incoming substances. The kidneys regulate blood chemistry and eliminate numerous water-soluble waste products. The bloodstream transports nutrients to where they are needed.
Now imagine delivering several truckloads of materials when the factory needs only one.
Some materials may be stored. Others are excreted. Some accumulate, and certain substances can cause toxicity.
This analogy helps explain why excess supplementation deserves attention.
Fat-soluble vitamins, including A and D, can accumulate and become harmful at excessive doses. Excess vitamin D may raise blood calcium and cause kidney injury.
Water-soluble vitamins are generally eliminated more readily, but that does not guarantee safety. Excess vitamin B6 may cause neuropathy, while high-dose niacin can injure the liver.
Importantly, the liver and kidneys do not necessarily become overworked simply because a person takes supplements. Harm depends on the nutrient, formulation, dose, duration, interactions and underlying health.
The body also doesn’t absorb only what it needs from food. Food can also provide excessive nutrients. However, typical dietary patterns generally deliver nutrients in lower concentrations, along with fibre, water, and other food components.
Concentrated supplements can bypass some of the practical limits of normal food intake.
This is why the dose matters.
What might dark urine and urinary discomfort be telling us?
Patients sometimes report dark urine, burning, irritation or discomfort while taking numerous supplements.
Bright yellow urine may simply reflect riboflavin (vitamin B2), which produces a harmless colour change.
But dark brown urine, persistent burning, blood in the urine, or urinary pain should never be automatically attributed to vitamin elimination.
Possible causes include dehydration, urinary infection, kidney stones, blood or muscle breakdown products, and liver or kidney disease.
People with persistent symptoms may need urine testing, kidney-function assessment, and other investigations.
The lesson is straightforward: urinary symptoms are clinical warning signs, not proof that the body is successfully detoxifying itself.
Precision nutrition: the right nutrient for the right person
Conventional medicine is increasingly using genetic and molecular information to guide selected treatments.
Pharmacogenomics can help predict how some people metabolise medicines, although it is not yet routinely useful for every drug.
Nutrigenomics investigates how genes influence responses to nutrients and how dietary exposures affect gene expression.
For example, genetic variation may influence caffeine metabolism, lactose digestion and aspects of lipid metabolism.
But genetic information is only one piece of the puzzle.
A person’s nutritional needs also depend on age, dietary intake, gut function, medications, disease activity, kidney function and lifestyle.
A genetic variant does not automatically establish a deficiency or justify lifelong supplementation.
The future of precision nutrition therefore requires combining genetic information with clinical assessment, validated biomarkers and meaningful outcomes.
Think of it as using a satellite navigation system.
Genetics provides part of the map. Blood tests describe current conditions. Symptoms indicate possible obstacles. Dietary assessment reveals the available resources.
Only by combining these signals can we choose a sensible route.
Are we testing the right nutrients?
Clinicians commonly measure vitamin D, especially when clinically indicated.
But other nutritional problems may remain undetected.
For example, people taking metformin for diabetes can develop vitamin B12 deficiency. Older adults may have impaired B12 absorption, while restrictive diets can increase the risk of iron, calcium or other nutrient shortfalls.
Rather than ordering expensive comprehensive nutrient panels for everyone, clinicians should use targeted testing.
A useful assessment might include B12 and a full blood count when risk factors or symptoms are present, ferritin when iron deficiency is suspected, or electrolytes and kidney function when supplements or medications create relevant risks.
In selected cases, methylmalonic acid can help clarify uncertain B12 results.
Routine testing of every B vitamin is rarely necessary. Some nutrient tests are poorly standardised or difficult to interpret.
The goal isn’t to produce the longest laboratory report.
It is to identify a clinically meaningful problem that can be corrected and monitored.
Gut health: the missing foundation
Imagine purchasing expensive fertiliser for a garden without checking whether the soil can support plant growth.
Something similar may happen when we prescribe nutrients without considering digestion and absorption.
The gastrointestinal tract breaks down food, absorbs nutrients, interacts with the immune system and supports an enormous microbial ecosystem.
Conditions such as coeliac disease, inflammatory bowel disease, pancreatic insufficiency and certain gastrointestinal surgeries can impair nutrient absorption.
Chronic constipation also deserves proper evaluation, although it does not automatically indicate malabsorption.
Supporting gut health may involve adequate dietary fibre, appropriate hydration, physical activity, identifying underlying disease and reviewing constipating medicines.
What about probiotics?
The science is more selective than marketing suggests. The American Gastroenterological Association’s clinical guideline found evidence for probiotic formulations in specific circumstances, but insufficient evidence to recommend routine probiotic use for many digestive disorders. [2]
Fermented foods such as live yoghurt and kefir can be useful dietary choices for many people, although they are not guaranteed substitutes for clinically indicated probiotics.
For people with suspected mast cell activation problems or histamine sensitivity, fermented foods may trigger symptoms and require individual assessment.
Restoring gut function matters, but it doesn’t mean everyone needs a probiotic capsule.
Do we need antioxidant supplements or a rainbow on the plate?
Our cells continuously produce reactive oxygen species as part of normal metabolism.
Imagine tiny sparks emerging from a working engine.
Some sparks are part of normal cellular signalling. Excessive, uncontrolled oxidative stress can damage tissue.
Antioxidants help maintain balance.
However, the aim is not to eliminate every reactive molecule. Some are essential for immune defence, adaptation to exercise and normal cell signalling.
High-dose antioxidant supplementation has not consistently shown the expected health benefits, and certain formulations can harm specific populations.
A more reliable starting point is a colourful, varied diet.
Think of the rainbow as a natural nutritional orchestra.
Red tomatoes provide lycopene. Orange carrots supply carotenoids. Purple berries contain anthocyanins. Green vegetables offer folate and numerous phytochemicals.
No single compound plays the entire symphony.
Eating a variety of plant foods delivers different compounds within a complex food matrix.
This is not evidence that food can treat every deficiency or replace necessary medical therapy. Rather, it supports using dietary patterns as the foundation, with targeted supplements when indicated.
Omega-3, omega-6 and individual metabolic differences
Omega-3 fatty acids have important roles in cellular membranes and biological signalling.
Oily fish such as salmon, sardines, herring and mackerel provide EPA and DHA.
Some people may benefit from omega-3 supplementation, particularly in specific clinical circumstances. Prescription-strength preparations also have defined uses, including certain lipid disorders.
But a high omega-6:omega-3 ratio alone does not establish a diagnosis or prove that supplements are necessary.
Omega-6 fatty acids are essential nutrients, not toxins. The balance between different fatty acids matters, but clinical decisions should consider the overall dietary pattern, triglycerides, cardiovascular risk and evidence for interventions.
For many adults, eating oily fish regularly is a sensible food-first strategy.
Those who do not eat fish may consider suitable alternatives, such as algae-derived DHA and EPA, based on their needs.
Should nutrients always travel through the gut?
Oral supplementation is convenient, but it is not universally effective.
Vitamin B12 injections may be appropriate for certain causes of deficiency, including some forms of malabsorption. High-dose oral B12 can also work in many circumstances.
Sublingual preparations are available, but evidence does not establish that they are routinely superior to swallowed supplements.
Transdermal delivery is well established for some medicines, including certain hormones, but evidence for many vitamin patches remains limited.
The skin is an effective barrier, not an open doorway through which every nutrient can pass.
Intravenous supplementation should generally be reserved for recognised medical indications, such as severe deficiency, inability to use the gastrointestinal tract or specific hospital treatments.
Select each route based on evidence, safety, and clinical need, not simply because it appears more advanced.
Young adults and older adults: different risks, different priorities
In younger adults, supplementation may be influenced by fitness trends, social media, restrictive diets and the pursuit of energy, beauty or longevity.
Certain groups have legitimate needs, including folic acid around conception, vitamin B12 for people following vegan diets, and vitamin D based on national guidance and individual risk.
In older adults, the challenges often change.
Reduced appetite, lower food intake, impaired absorption, frailty, chronic illness and multiple medications can increase nutritional vulnerability.
Yet older adults may also be more susceptible to adverse effects from inappropriate supplementation, particularly when kidney function is reduced.
The answer is neither to prescribe supplements universally nor to discourage them indiscriminately.
It is to recognise that nutritional requirements evolve throughout life.
The five questions every supplement prescription should answer
Before prescribing or continuing a supplement, I believe clinicians and patients should be able to answer five questions.
- Why is it needed?
Is there a confirmed deficiency, established risk or evidence-based clinical indication?
- What is the safest effective dose and form?
Consider age, organ function, medication interactions and overlapping ingredients.
- How long should it continue?
Some treatments are temporary. Others, such as B12 replacement for irreversible absorption disorders, may be lifelong.
- How will success and safety be assessed?
Use symptoms, relevant laboratory markers and agreed clinical outcomes.
- Can dietary intake eventually replace it?
Where appropriate, move towards sustainable food sources rather than indefinite supplementation.
This approach fits with NICE guidance on structured medication reviews, which explicitly includes prescribed, over-the-counter and complementary products. [3]
For complex patients, coordination between their doctor, pharmacist, dietitian and relevant specialists is essential. Hormonal treatment for confirmed adrenal insufficiency, for example, cannot be replaced by nutritional or so-called adrenal support supplements.
If you found this discussion useful, you may be interested in my recently published book, “Your Metabolic Shift”, which explores these concepts in greater depth.
Frequently asked questions
- Is taking a daily multivitamin harmful?
Not necessarily. Standard-dose multivitamins are generally well tolerated, but benefits depend on dietary adequacy and individual risk. Multiple overlapping products can lead to excessive intake.
- Can supplements damage the liver or kidneys?
Yes, certain supplements can cause toxicity, especially at high doses or in susceptible people. Herbal products and contaminated formulations can also present risks. However, normal supplement use does not automatically cause organ damage.
- Should everyone test their vitamin levels?
No. Targeted testing based on symptoms, diet, medications and medical history is usually more useful than broad routine screening.
- Can nutrigenomics tell us exactly which supplements to take?
Not yet. Genetic testing can provide useful information in selected settings, but most commercial nutrigenomic recommendations lack sufficient evidence to dictate precise supplement prescriptions.
- Are food-based nutrients always better than supplements?
Food is generally the preferred foundation of nutrition, but supplements may be essential when diet cannot meet requirements or absorption is impaired.
- When should supplements be stopped?
When the indication has resolved, there is no meaningful benefit, risks outweigh benefits, or the planned course has ended. Some deficiencies require long-term treatment. Review decisions with the relevant clinician.
The future: fewer guesses, better outcomes
Precision nutrition should not mean prescribing a personalised mountain of capsules.
It should mean understanding the individual well enough to prescribe only what is necessary.
We need better coordination between conventional and nutritional medicine, improved recognition of genuine deficiencies, greater awareness of excessive intake, and clear plans for monitoring and discontinuation.
We also need to distinguish proven clinical treatments from attractive but unvalidated ideas about detoxification, antioxidant support and genetic optimisation.
This becomes especially important for patients with multiple chronic illnesses.
The most valuable intervention may sometimes be adding a nutrient.
At other times, it may be removing an unnecessary supplement, correcting an underlying digestive disorder, improving food quality or preventing an interaction.
Final reflection
We have entered an era when it is easier than ever to buy nutrients, but not necessarily easier to know whether we need them.
The future of healthcare should not be a competition between pharmaceuticals, supplements and food.
It should be a partnership built on scientific evidence, individual biology and careful clinical judgement.
Perhaps the most important question in precision nutrition is no longer, “What else can we add?” but “What does this person truly need—and what can we safely leave out?”
That is the difference between simply taking more and genuinely achieving better health.
This article is intended for educational purposes only and should not replace personalised medical advice. Readers with existing medical conditions should consult their healthcare professional before making significant dietary or lifestyle changes.
References and further reading
- NHS. Vitamins and minerals: B vitamins and folic acid. National Health Service. NHS guidance on B vitamins and supplement safety.
- Su GL, Ko CW, Bercik P, et al. AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020;159(2):697–705. DOI: 10.1053/j.gastro.2020.05.059.
- National Institute for Health and Care Excellence (NICE). Medicines optimisation: the safe and effective use of medicines to enable the best possible outcomes. NICE Guideline NG5. 2015. NICE NG5.
- EFSA Panel on Nutrition, Novel Foods and Food Allergens. Scientific opinion on the tolerable upper intake level for vitamin B6. EFSA Journal. 2023;21(5):8006. DOI: 10.2903/j.efsa.2023.8006. The panel established an adult upper intake level of 12 mg/day, including dietary and supplemental intake.
- US Preventive Services Task Force. Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer: Preventive Medication. 2022. USPSTF recommendation statement.
- National Institutes of Health, Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. NIH vitamin D evidence and toxicity review.
- NHS Specialist Pharmacy Service. A person-centred approach to polypharmacy and medication review. Published January 2025; updated February 2026. NHS SPS clinical guidance.
- US Food and Drug Administration. Biotin Interference with Troponin Lab Tests. FDA laboratory safety information. High-dose biotin can interfere with certain diagnostic blood tests, illustrating another overlooked risk of supplementation.
- British Geriatrics Society. Comprehensive Geriatric Assessment: Medication History and Review. 2025. British Geriatrics Society guidance.
- NHS England. Structured Medication Reviews and Medicines Optimisation. NHS England medication review framework.
