Daniel Fletcher
Why supplements are not a shortcut
A supplement is exactly what its name suggests: something that tops up an existing shortfall. It cannot make up for a diet low in fruit and vegetables, poor sleep, or a week spent sitting down. In the UK, most adults who eat a varied diet and get outside regularly meet their vitamin and mineral needs from food alone, and the evidence for routine supplementation in healthy people is thin. Where supplements do earn their place is in specific, well-defined situations: a diagnosed deficiency, a restricted diet, a particular life stage, or a season of limited sunlight. A supplement supports health; it does not create it.
Vitamin D: the one the UK advises for almost everyone
Because of our northern latitude, the sun here is only strong enough for skin to make vitamin D between roughly late March and the end of September. From October to March, the NHS advises adults and children over the age of one to consider a daily supplement of 10 micrograms (400 international units).
Those who cover their skin, spend most of the day indoors, or have darker skin may benefit from taking it all year round. Vitamin D matters for bone strength and muscle function, and low levels are common in the UK. Very high doses are not better: taking more than 25 micrograms a day without medical advice is not recommended, as it can raise blood calcium over time.
Vitamin B12 and folate: vital for certain diets and life stages
Vitamin B12 occurs naturally in meat, fish, eggs and dairy, so most people get plenty. Those at risk of low levels include vegans, some vegetarians, older adults whose stomach acid has reduced with age, and anyone taking long-term medication for acid reflux or diabetes. Adults need about 1.5 micrograms a day, and a daily supplement is a cheap, sensible safeguard for anyone avoiding animal foods.
Folate is a separate B vitamin, found in green leafy vegetables, pulses and fortified cereals. It is especially important in the earliest weeks of pregnancy, when the neural tube forms. Women are advised to take 400 micrograms of folic acid daily from before conception until 12 weeks of pregnancy. If you have a higher risk of neural tube defects, a doctor may recommend a larger dose.
Iron, calcium and magnesium: useful only when there is a genuine gap
Iron deficiency is one of the most common nutritional problems in the UK, particularly among menstruating women, but tiredness alone is not proof of it. Iron supplements are worth taking only after a blood test has confirmed low iron stores, because too much iron causes constipation and, rarely, more serious harm. Adults need around 8.7mg a day (14.8mg for women up to 50). Red meat, pulses, dark green vegetables and fortified cereals all contribute, and a glass of orange juice with a meal helps your body absorb plant iron, while tea and coffee at the same time hinder it.
Calcium, needed at about 700mg a day, is best obtained from dairy, fortified plant milks, tinned fish with bones and leafy greens. Supplements are rarely needed and can cause stomach upset. Magnesium has become fashionable for sleep and muscle cramps, but the evidence is mixed; nuts, seeds, wholegrains and beans are reliable sources, and large supplemental doses often loosen the bowel.
Vitamin C and multivitamins: popular, rarely necessary
Adults need just 40mg of vitamin C a day — easily met by a single orange or a portion of peppers. Mega-doses do not prevent colds in the general population, though they may modestly shorten one. Multivitamins are not harmful for most people, but they are no substitute for food and can quietly push you past safe limits if combined with other products. Bear in mind that high-dose vitamin A should be avoided in pregnancy, and very high doses of vitamin B6 over long periods can affect the nerves.
Practical steps before you buy anything
- Fix food first: one extra portion of vegetables, a few eggs, or a handful of nuts often closes the gap a tablet was meant to fill.
- Check whether you are in a group with official advice — vitamin D in winter, folic acid before pregnancy, B12 if you are vegan.
- Ask your GP or pharmacist before starting a supplement if you take prescription medicines. Iron, calcium and magnesium can block the absorption of thyroid tablets, and vitamin K can interfere with warfarin.
- Stick to the label dose. More is not better, and "natural" does not mean risk-free.
- Tell your GP, nurse or midwife about anything you take, including herbal products.
- Buy from a reputable UK retailer and check for a supplement quality mark, so what is on the label is what is in the tablet.
For many people, a modest vitamin D supplement through the winter, a B12 supplement if they avoid animal foods, and a blood test before anything else, is all the supplementation they need. Eating well remains the foundation, and a conversation with a health professional is the best way to decide whether a supplement adds anything at all.
