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Iron Supplement Without Constipation: What Actually Helps (UK Guide)
Looking for an iron supplement without constipation? Why iron upsets the gut, and the practical steps — sensible dose, well-tolerated form, taking it with food and vitamin C — that genuinely help.
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Best Multivitamin Supplements UK: How to Compare Formulas
Reviewed and updated: 25 July 2026 Best multivitamin supplements UK: how to compare formulas without the marketing noise The best multivitamin supplements in the UK are not the ones with the longest ingredient list or the boldest label, they are the ones whose formula actually matches the gaps in your own diet, uses well-absorbed forms at sensible doses, and stays inside safe upper limits. This guide gives you a clear, honest framework for comparing formulas so you can decide what is genuinely worth your money. TL;DR: what to look for in a multivitamin What it is: a single product combining several vitamins and minerals, usually somewhere around the Nutrient Reference Value (NRV) for each. Who it is for: people who want a convenient nutritional baseline, and specific groups (vegans, older adults, people on restricted diets) who are more likely to fall short on certain nutrients. Key checks: meaningful doses (a nutrient at roughly 15% NRV or more is doing a real job), well-absorbed forms, vitamin D present at a useful level, zinc balanced with copper, and amounts that respect safe upper limits. Honest caveat: in adults who already eat well, large studies have not shown that a daily multivitamin lowers the risk of death. Think of it as insurance against shortfalls, not a health upgrade on top of a good diet. 1. Start with the NRV and the 15% rule Every vitamin and mineral on a UK label is shown as a percentage of its Nutrient Reference Value (NRV), the reference amount for an average adult. This single number is the quickest way to sort a real formula from a decorative one. As a working rule, a nutrient needs to be present at roughly 15% of its NRV per daily dose before it is contributing anything meaningful. If you see a nutrient listed at a token 2 to 3% NRV, treat it as label decoration rather than a real contributor, it is there to lengthen the ingredient list, not to help you. 2. Nutrient coverage: breadth that matches your diet A good multivitamin covers the nutrients people commonly fall short on, rather than padding the label with forty obscure extras. For most UK adults the useful core is the B vitamins, vitamin D, magnesium, zinc, selenium and, for some people, iron. At meaningful doses the reasons to include them are well established: vitamin D contributes to the normal function of the immune system, magnesium contributes to the reduction of tiredness and fatigue, and zinc contributes to the protection of cells from oxidative stress. In other words, these are the workhorses, and a sensible formula gets them right before reaching for anything exotic. 3. B vitamins: the forms matter A complete formula usually includes all eight B vitamins (B1, B2, B3, B5, B6, B7/biotin, B9/folate and B12). Better formulas use the forms the body can use directly, such as methylcobalamin for B12 and methylfolate (5-MTHF) for folate. These can matter for people with common genetic variations in folate processing. An honest note: for most people with normal folate metabolism, ordinary folic acid is also converted efficiently, so methylated forms are a sensible default rather than a proven advantage for everyone. B12 contributes to normal energy-yielding metabolism and to the reduction of tiredness and fatigue, though it only relieves tiredness that is actually caused by a shortfall. 4. Vitamin D: get the dose right The NHS recommends 10 micrograms (400 IU) of vitamin D a day, and advises that everyone in the UK consider a daily supplement in autumn and winter, when sunlight is too weak for the skin to make enough. Many multivitamins quietly under-dose vitamin D, so check the figure. Choose D3 (cholecalciferol), which raises blood levels more effectively than D2. Vitamin D contributes to the normal function of the immune system and to the maintenance of normal bones. On the safety side, the NHS advises adults not to take more than 100 micrograms (4000 IU) a day from supplements. See our UK guide to vitamin D3 and K2 dosing for more. 5. Zinc, and why copper belongs with it Zinc contributes to the normal function of the immune system and to the maintenance of normal hair, skin and nails. A multivitamin only needs a modest amount. The important detail is that sustained higher-dose zinc can interfere with copper absorption, which is why a small amount of copper is often added alongside it. The UK and EU safe upper limit for zinc from supplements is 25 mg a day, so watch out for stacking a high-zinc multivitamin with a separate zinc product. Our guide to zinc forms, copper and dosage covers this in detail. 6. Selenium: an antioxidant mineral with a narrow window Selenium contributes to the protection of cells from oxidative stress and to the normal function of the immune system. A daily amount near the NRV (around 55 to 70 micrograms) is plenty. Selenium has a relatively narrow margin between enough and too much: the EFSA tolerable upper intake level is 300 micrograms a day, so avoid stacking several selenium sources at once. 7. Iron: include it only if you need it Iron contributes to the reduction of tiredness and fatigue and to normal oxygen transport in the body, but it only helps if you are genuinely low. Many adults, particularly men and post-menopausal women, do not need extra iron, and too much can cause constipation and, rarely, a build-up over time. Iron-free or low-iron multivitamins exist for exactly this reason. If you suspect low iron, ask for a ferritin blood test rather than guessing, and read our practical UK guide to raising ferritin. 8. Respect the safe upper limits The risk with a high-strength everything multivitamin is not the multivitamin alone, it is stacking it with other supplements until you cross a safe limit. Useful reference points for adults are: vitamin D 100 micrograms (4000 IU) a day, zinc 25 mg a day, and selenium 300 micrograms a day. Preformed vitamin A (retinol) should be kept low, especially in pregnancy. The more single-nutrient products you take, the more carefully you need to add up the totals. Interactions and who should be cautious Pregnancy: avoid high preformed vitamin A (retinol) and choose a pregnancy-specific formula that provides folic acid; speak to your midwife or GP. Warfarin and other blood thinners: vitamin K affects how these medicines work, so any K-containing product should be discussed with your GP or pharmacist. Kidney disease: be cautious with mineral loads (including magnesium and potassium) and take medical advice first. Biotin: high doses can interfere with some laboratory blood tests (including thyroid and certain heart tests), so tell the person taking your blood that you use it. Medication timing: iron, zinc and calcium can reduce absorption of some antibiotics and thyroid medicine, so separate them by a few hours. Suitability: vegan, vegetarian and allergen-free If you follow a plant-based diet, check that the vitamin D is D3 from a vegan source such as lichen, and that the capsule shell is not gelatin. Look for clear gluten-free, dairy-free and nut-free declarations if you have allergies. A trustworthy label states all of this plainly rather than leaving you to guess. Clean label, quality and value Prefer formulas with minimal fillers and no unnecessary colours or sweeteners, and a transparent ingredient list that names the exact forms used. At Pure Vitamins our products are formulated in the UK and tested for purity and heavy metals at our GMP-certified facility. On value, look at the cost per day rather than the headline price, and check the capsule count so you know how long a pack lasts. Does a multivitamin actually work? Here is the honest picture, and it is genuinely mixed. According to PubMed, a 2024 analysis of nearly 400,000 generally healthy US adults across three large cohorts found that regular multivitamin use was not associated with a lower risk of death over up to 27 years of follow-up (Loftfield and colleagues, JAMA Network Open, https://doi.org/10.1001/jamanetworkopen.2024.18729). On the other side of the ledger, the COSMOS randomised trials found something more encouraging for older adults: in COSMOS-Web, a daily multivitamin improved memory compared with placebo (Yeung and colleagues, American Journal of Clinical Nutrition, https://doi.org/10.1016/j.ajcnut.2023.05.011), and a pooled analysis across three COSMOS cognitive substudies reported a modest benefit for global cognition and memory, roughly equivalent to reducing cognitive ageing by around two years (Vyas and colleagues, American Journal of Clinical Nutrition, https://doi.org/10.1016/j.ajcnut.2023.12.011). The effects were modest, and the participants were older adults, so this is not a promise for everyone. The sensible reading is that a multivitamin earns its place by correcting a real shortfall, from diet, life stage or restricted eating, rather than by adding benefit on top of an already good diet. Match the formula to your gaps and it can be a tidy nutritional baseline. How Pure Vitamins approaches this Rather than crowd forty nutrients into one tablet at token doses, we focus on well-dosed formulas you can combine to suit your needs. The Immunity & Energy Support Trio pairs Zinc, Vitamin D3+K2 and Magnesium Glycinate, three of the most commonly useful additions for UK adults, at meaningful doses and in well-absorbed forms. If your priority is everyday energy, our guide to vitamins for tiredness and our immunity guide are good next reads. You can also browse the full range on our home page. Shop the Immunity & Energy Support Trio Frequently asked questions What is the best multivitamin in the UK? There is no single best multivitamin for everyone. The best one for you provides the nutrients your diet is short on, at meaningful doses (at least 15% NRV), in well-absorbed forms, and within safe upper limits. Match the formula to your own gaps rather than chasing the longest ingredient list. Do I really need a multivitamin? Not necessarily. People who eat a varied, balanced diet may get little from one, while vegans, older adults and people on restricted diets are more likely to benefit from targeted nutrients such as vitamin D, B12 and, sometimes, iron. Is it safe to take a multivitamin every day? For most adults a sensibly dosed multivitamin is fine daily. The main risk is stacking it with other supplements and exceeding safe limits, for example more than 100 micrograms (4000 IU) of vitamin D, 25 mg of zinc or 300 micrograms of selenium per day. Should a multivitamin contain iron? Only if you need it. Iron is useful for people who are genuinely low, but unnecessary iron can cause constipation and build-up. If in doubt, ask for a ferritin test before choosing an iron-containing formula. Does a multivitamin help memory or brain function? The evidence is early but interesting. The COSMOS randomised trials found a modest memory and cognition benefit from a daily multivitamin in adults aged 60 and over, while large mortality studies show no benefit in generally well-nourished adults. It is best seen as a possible small edge for older adults, not a proven brain boost for everyone. Dr. Miron, Founder of Pure Vitamins UK. This article is for general information and education only and is not medical advice. Food supplements are not a substitute for a varied, balanced diet and a healthy lifestyle. If you are pregnant, breastfeeding, taking medication or living with a health condition, speak to your GP or pharmacist before starting a supplement. If that is useful, see also why medical research references matter.
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