Food first, supplements second

A multivitamin feels like an easy insurance policy. One tablet with breakfast, a small sense of security, and you can stop worrying about whether you ate enough leafy greens this week. The trouble is that a supplement can never quite replicate what food does. Whole foods deliver vitamins and minerals alongside fibre, healthy fats, phytonutrients and thousands of compounds we are still learning about, all working together in ways a tablet cannot copy.

The other issue is need. Most people eating a varied diet, with plenty of vegetables, fruit, wholegrains, pulses, eggs, dairy or fortified alternatives, and some fish or lean meat, are already meeting the majority of their requirements. Adding a multivitamin on top does not usually make a well-nourished person healthier. In some cases, it simply produces expensive urine.

So the honest answer to "do I need one?" is: sometimes, but not automatically. It depends on your diet, your lifestyle, your gut, your health status and your stage of life.

When a multivitamin genuinely earns its place

There are situations where a supplement is more than a comfort blanket. In the UK, specific nutrients are recommended for specific groups because food alone often falls short:

• Vitamin D: the NHS advises 10 micrograms daily during autumn and winter, and year-round for anyone who covers their skin or spends most of the day indoors. This is one nutrient food rarely supplies in enough quantity.
• Vitamin B12: essential for anyone following a vegan diet, and worth checking if you take long-term metformin or acid-reducing medication.
• Folic acid: 400 micrograms daily before conception and through the first twelve weeks of pregnancy.
• Iron: sometimes needed during pregnancy, with heavy periods, or after blood loss, but only on the basis of a blood test.
• Calcium and vitamin D together for some post-menopausal women and older adults.

If you fall into one of these groups, a targeted supplement usually makes more sense than a broad multivitamin, because you get a useful dose of what you actually need rather than a sprinkle of everything.

Your gut decides how much you absorb

Here is the part that rarely makes it onto the label. Swallowing a nutrient is not the same as absorbing it. Your stomach acid, pancreatic enzymes, the health of your small intestine lining and the balance of your gut bacteria all influence how much of a vitamin actually reaches your bloodstream.

Conditions such as coeliac disease, inflammatory bowel disease, low stomach acid, small intestinal bacterial overgrowth and chronic diarrhoea can all reduce absorption. So can long-term use of proton pump inhibitors. If your gut is struggling, a multivitamin may deliver far less than you expect, and the first step is usually investigating why rather than simply increasing the dose.

A fibre-rich, plant-diverse diet supports the gut bacteria that help produce and activate certain vitamins, including some B vitamins and vitamin K. In that sense, feeding your gut well is itself a form of supplementation.

Food sensitivity and supplements: a tricky overlap

If you react to certain foods, supplements deserve a closer look. Tablets and capsules contain more than active nutrients: binders, fillers, flavourings, sweeteners such as sorbitol and mannitol, and traces of lactose, gluten or soya. For someone with a genuine sensitivity, these excipients can trigger bloating, wind, loose stools or skin flare-ups.

Keep a simple symptom diary for a fortnight if you suspect a link, noting what you take, when, and how you feel. Be cautious about self-diagnosing, though. True food allergy, coeliac disease and lactose intolerance are medical diagnoses, and a multivitamin is rarely the sole culprit. If symptoms are persistent or severe, speak to your GP before cutting out whole food groups.

Reading the label like a practitioner

Not all multivitamins are created equal, and a higher dose is not automatically better.

• Check the percentage of the nutrient reference value (NRV) for each vitamin and mineral, rather than being impressed by long lists.
• Be wary of mega-doses. Fat-soluble vitamins A, D, E and K accumulate in the body, and high-dose vitamin A (retinol) is unsafe in pregnancy.
• Watch the iron. Unless you have been tested and found deficient, extra iron can cause constipation and stomach upset.
• Separate the competitors. Calcium and iron compete for absorption, so a single tablet containing large amounts of both is a compromise.
• Check for interactions. Vitamin K can affect warfarin, and some nutrients interfere with thyroid medication. Ask your pharmacist if you take prescribed medicines.

A practical way to decide

Start with a week of honest food tracking. Note your portions of vegetables and fruit, your sources of protein, oily fish, dairy or fortified alternatives, and how much time you spend outdoors. Most people find one or two clear gaps rather than a general deficiency.

Then fill those gaps with food where you can, and consider a targeted supplement where you cannot. If you do take a multivitamin, treat it as a trial rather than a lifelong habit: take it consistently for eight to twelve weeks, note any changes in energy, digestion or skin, and review. If you notice nothing and your diet is strong, you can reasonably stop.

Above all, remember that a supplement supplements. It tops up a diet that is already doing most of the work, and it works best when your gut is healthy enough to use it.