What vitamin should I take if I don't eat enough?

Reviewed and updated: 4 September 2026

What vitamin should I take if I don't eat enough? The short answer

What vitamin should I take if I don't eat enough is one of the most sensible questions anyone can ask me, and the honest answer is that it is rarely one vitamin. When your overall food intake drops, almost everything in your diet drops with it, so the sensible starting point is a good general multivitamin and mineral at close to 100% NRV, then a separate top-up of the two or three nutrients that fall short fastest: vitamin D, vitamin B12 and, for many women, iron. That combination covers the widest gap for the least fuss.

I want to be clear about what this article is and is not. This is written for people who are simply not eating very much, whether that is because your appetite has gone quiet, you have been unwell, you are older and food has stopped appealing, or your diet has narrowed down to a handful of foods you can face. It is not about deliberately cutting calories to lose weight. If that is what you are doing, my guide to supplements while eating less is the better read, and the two articles are meant to sit side by side.

The quick answer

• What it is. A small, simple stack rather than one magic tablet: a broad multivitamin and mineral, plus vitamin D, plus B12, plus iron if your intake of meat or fortified foods has dropped.
• Who it is for. Anyone whose food intake has genuinely fallen: low appetite, recovery from illness, older age, a very narrow diet, or long stretches of skipped meals.
• The key thing to know. Eating less lowers how much of each nutrient goes in, not how well you absorb it. So the fix is usually about topping up intake, not about anything exotic.
• One honest caution. If your appetite has dropped without you choosing it, or your weight is falling, a supplement is not the answer on its own. That is a conversation to have with your GP.

Why eating less lowers your intake rather than your absorption

This is the part almost every article skips, and it changes how you should think about the problem. Your gut does not become worse at absorbing zinc because you had toast instead of dinner. What happens is much simpler. Vitamins and minerals arrive in food, so when the volume of food falls, the volume of nutrients falls in almost exact proportion. A day that used to deliver 2,200 calories across meat, dairy, vegetables, grains and fruit might now deliver 1,100 calories across tea, toast and a biscuit, and every micronutrient in that first list has quietly halved or worse.

There is a nice piece of research that makes this concrete. Calton and Calton analysed the suggested daily menus of four well-known, carefully constructed diet plans and checked them against the reference intakes for 27 micronutrients. Not one of the four menus met the reference intake for all 27, and on average they hit sufficiency for fewer than 12 of them at around 1,750 calories a day. Vitamin D, biotin, vitamin E, chromium, iodine and molybdenum came out consistently low across all four (Calton and Calton, 2010). If a menu written by a professional falls short at that intake, an unplanned day of picking at food will fall a lot shorter.

The same pattern shows up in real people rather than paper menus. A Spanish study of 190 older adults at nutritional risk, published in the British Dietetic Association's own journal, found their calories and protein were broadly fine, and yet calcium, vitamin D, vitamin E and folate intakes all came in below two thirds of the recommended amount, with more than an 85% probability of inadequate intake for each (Fernandez-Barres et al., 2016). That is the exact trap I want you to sidestep. A small diet can look adequate on the headline numbers and still be missing several of the things that matter most.

The nutrients that run short first when you are not eating much

Here is my nutrient-by-nutrient answer, with the UK reference numbers so you can actually check a label rather than guess. Where a nutrient has an authorised wording in the GB nutrition and health claims register, I have used that exact wording, because vague phrases like "supports wellbeing" tell you nothing.

Vitamin B12

B12 comes almost entirely from animal foods: meat, fish, eggs, dairy, and fortified cereals or plant milks. It is usually the first casualty when someone stops cooking proper meals, and it is the one I would not skip. The UK reference nutrient intake for adults is 1.5 micrograms a day, and the nutrient reference value used on labels is 2.5 micrograms. Supplement doses are typically far higher than both, because absorption of a single large dose is limited. B12 contributes to normal energy-yielding metabolism, to the reduction of tiredness and fatigue, and to normal red blood cell formation. If you would like the full picture on forms and doses, I have written a longer UK guide to vitamin B12.

Iron

Iron intake falls fast when red meat, pulses and fortified breakfast cereals drop out of a diet, and it matters more for some people than others. The UK reference nutrient intake is 14.8 mg a day for women aged 19 to 50, and 8.7 mg for men and for women over 50. The label NRV is 14 mg. Iron contributes to normal formation of red blood cells and haemoglobin, to normal oxygen transport in the body, and to the reduction of tiredness and fatigue. Two practical notes. Vitamin C increases iron absorption, so taking iron with something like a small glass of orange juice is genuinely useful. And tea, coffee and calcium all reduce absorption, so leave a gap of an hour or so. My article on how to increase ferritin goes into the stores side of this properly.

Vitamin D

Vitamin D is the odd one out, because you get very little of it from food at the best of times. Between October and March at UK latitudes the sunlight is too weak for your skin to make any, which is why official advice here is that everyone should consider a daily 10 microgram supplement through autumn and winter, and that some groups should take it all year round: people who are indoors most of the time, people who cover most of their skin, and people with darker skin tones. Vitamin D contributes to the maintenance of normal bones, to normal muscle function, and to the normal function of the immune system. If you take one thing from this article and you live in Britain, take that. There is more detail in my piece on vitamin D in winter in the UK.

Calcium

Calcium is concentrated in a small number of foods, mostly dairy, fortified plant milks, tinned fish with bones, and some leafy greens. Lose the milk on your cereal and the cheese in your sandwich and a large chunk of your daily intake goes with it. The UK reference nutrient intake for adults is 700 mg a day, and the label NRV is 800 mg. Calcium is needed for the maintenance of normal bones and teeth, and it contributes to normal muscle function. This is one where food genuinely beats a tablet if you can manage even small amounts, because 200 ml of milk gets you roughly a third of the way there in one go.

Folate

Folate comes from green vegetables, pulses, and fortified cereals, all of which tend to disappear early from a shrinking diet. The UK reference nutrient intake is 200 micrograms a day for adults, which is also the label NRV. Folate contributes to normal blood formation, to normal amino acid synthesis, and to the reduction of tiredness and fatigue. Women who could become pregnant are advised to take 400 micrograms of folic acid daily, which is a separate piece of UK advice and worth following regardless of appetite.

Zinc

Zinc tracks protein intake closely, so it drops when meat, shellfish, dairy, nuts and seeds drop. The UK reference nutrient intake is 9.5 mg a day for men and 7 mg for women, with a label NRV of 10 mg. Zinc contributes to normal macronutrient metabolism, to the maintenance of normal hair, skin and nails, and to the normal function of the immune system. There is a long-standing observation that zinc status and taste perception are linked, which is worth knowing if food has started tasting like very little, although it is not something to self-diagnose, and I have gone into that link and the other nutrients involved in which vitamins can help increase appetite. My guide to zinc forms, copper and dosage explains why a decent zinc product includes a little copper.

Magnesium

Magnesium sits in wholegrains, nuts, seeds, pulses and leafy greens, and UK intakes are often below the reference even in people eating normally. The reference nutrient intake is 300 mg a day for men and 270 mg for women, with a label NRV of 375 mg. Magnesium contributes to normal energy-yielding metabolism, to normal muscle function, to normal functioning of the nervous system, and to the reduction of tiredness and fatigue. If you want to compare forms sensibly, start with my guide to choosing a magnesium supplement in the UK.

The rest of the B group and vitamin C

Thiamine, riboflavin, niacin and vitamin B6 all contribute to normal energy-yielding metabolism, and they come from a wide spread of everyday foods, so they thin out gradually rather than crashing. Vitamin C contributes to normal collagen formation for the normal function of skin, bones, cartilage and blood vessels, to normal immune function, and to the reduction of tiredness and fatigue. A standard multivitamin covers this whole group comfortably, which is one of the better arguments for starting there rather than buying eight separate bottles.

Who tends to under-eat without meaning to

It helps to know whether you are in one of the groups where this is common, because it changes how urgently you should act.

• Older adults. Appetite and food intake genuinely decline with normal ageing, and researchers call it the anorexia of ageing. A review of the endocrinology behind it points to shifts in cholecystokinin, leptin, ghrelin and various cytokines as part of the explanation (Chapman, 2004). It is not laziness or fussiness, it is physiology.
• Anyone recovering from illness, surgery or a course of treatment, where appetite takes weeks to come back.
• People whose diet has narrowed, whether through sensory sensitivity, low mood, grief, or simply cooking for one and losing interest.
• Vegans and vegetarians eating small amounts, because B12, iron and often zinc are already harder to reach on a plant-based diet, and a small plant-based diet compounds it.
• People on very restricted diets for medical reasons, including some elimination diets, where the restriction itself removes whole food groups.
• Anyone eating very little for a long stretch of time, since stores of some nutrients, notably iron and B12, run down slowly and the shortfall can be invisible for months.

Food first, and what that actually looks like on a small appetite

Telling someone with no appetite to "eat a balanced diet" is not advice, it is a shrug. Here is what food-first actually means when you can only manage a little.

• Go for nutrient density, not volume. A boiled egg, a small pot of full-fat yoghurt, a handful of nuts, a slice of oily fish on toast. Small things that carry a lot.
• Fortified foods do a surprising amount of the work. Most UK breakfast cereals and plant milks are fortified with B vitamins, iron, calcium and often vitamin D, and a small bowl still delivers.
• Drinkable calories are easier than chewable ones. Milk, a milky coffee, a smoothie with yoghurt and fruit, or a soup with lentils stirred in.
• Little and often beats three proper meals when the sight of a full plate puts you off.
• Cold and plain foods are often more tolerable than hot, strong-smelling ones when appetite is low.
• Do not fill up on tea and water right before eating. Drink between meals instead.

The point of supplements here is to sit behind that, not to replace it. Food brings protein, fibre, energy and hundreds of compounds no tablet contains.

How to choose a supplement when you are eating very little

This is where most people waste money, so I will be blunt about what I look for.

• Start broad, then top up. One multivitamin and mineral near 100% NRV across the board, then single products only for the nutrients you know are short.
• Check the %NRV column, not the front of the box. Something at 8% NRV is decoration. For a general top-up you want most nutrients somewhere between 50% and 100% NRV.
• Avoid megadoses. When your intake is already low, the goal is to fill a gap, not to overshoot it by twenty times. High doses are where the safety issues live.
• Look at the form for the ones that matter. Magnesium glycinate is gentler on the stomach than oxide. Iron as ferrous fumarate or bisglycinate is usually better tolerated than sulphate. Vitamin D3 is the form to want.
• Fewer tablets is a real feature. If swallowing is the bottleneck, a stack you can actually take beats a perfect one you cannot.
• Look for straight answers about quality. Everything we make is formulated in the UK and tested for purity and heavy metals at our GMP-certified facility, and a brand that will not tell you that much is telling you something.

If you want the longer version of how to read a formula properly, my guide to comparing UK multivitamin formulas walks through it label by label.

How much is too much: the UK limits worth knowing

Taking more when you are eating less feels intuitive, and it is exactly the wrong instinct. These are the UK numbers I would want you to have in your head.

• Vitamin B6. NHS advice is not to take more than 10 mg a day from supplements unless a doctor has told you to. High intakes over long periods have been linked with loss of feeling in the arms and legs. This is the single most common overshoot I see on B complex labels, so check yours.
• Folic acid. Adults are advised not to exceed 1 mg a day. There is a genuine debate behind that number, which I come back to below.
• Vitamin D. Do not take more than 100 micrograms, which is 4,000 IU, a day. The 10 microgram daily amount recommended for autumn and winter is nowhere near this.
• Zinc. Do not exceed 25 mg a day from supplements. Long-term high zinc interferes with copper.
• Iron. Do not take more than 17 mg a day from supplements unless advised. Higher amounts commonly cause constipation and nausea, and iron is genuinely dangerous in overdose, particularly for children.
• Magnesium. Keep supplemental magnesium at or below 400 mg a day. Above that you will usually find out via your gut.
• Selenium. Do not exceed 350 micrograms a day.
• Vitamin C. Above about 1,000 mg a day you may get stomach pain and diarrhoea, which is the last thing you need on a small appetite.

The folic acid and B12 question, honestly

You will read in a lot of places that folic acid "masks" B12 deficiency. It is worth understanding what is actually being argued, because the evidence is not settled. Reynolds reviewed the literature and argued that the 1 mg upper level is unsound, and that there is already evidence of harm to the nervous system from long-term folic acid between 0.5 and 1 mg in people who are low in B12 (Reynolds, 2016). A later review by van Gool and colleagues went back over the 1945 to 2017 literature and reached the opposite conclusion, finding that the masking concept does not hold up as usually described and that the 1 mg upper level is safe (van Gool et al., 2020). Two careful reviews, two different readings. My practical takeaway is unchanged and uncontroversial: if you are supplementing folate and you are also in a group at risk of low B12, cover both rather than one, and stay inside the 1 mg folic acid limit.

How and when to take them

• Fat-soluble vitamins go with food that contains fat. Vitamins A, D, E and K absorb considerably better alongside a meal with some fat in it. On a small appetite, even a spoon of yoghurt or a bit of butter on toast is enough to help.
• Water-soluble vitamins are more forgiving. The B group and vitamin C can go with or without food, though some people find B vitamins on an empty stomach a bit much.
• Iron likes vitamin C and dislikes tea, coffee and calcium. Space it away from your cup of tea by an hour where you can.
• Space iron away from levothyroxine by at least four hours if you take it, and check the timing of any other medicines with your pharmacist.
• Zinc and iron compete, so if you take both at high doses, take them at different times of day.
• Consistency beats timing. A tablet taken every day with breakfast will do more for you than a perfectly optimised schedule you abandon in a fortnight.

Fluids and electrolytes when you are eating very little

Something people forget: a decent share of your daily fluid and a good chunk of your sodium and potassium come from food, not drinks. When you stop eating properly, both drop at once, and the light-headedness, headaches and muscle cramps that follow often get blamed on the lack of food when the real problem is fluid and salt. If you have been eating very little, keep drinking steadily through the day, do not cut salt out of what little you are eating, and reach for potassium-rich foods like potatoes, bananas, beans and yoghurt where you can manage them. If you are also losing fluid through vomiting or diarrhoea, that is a pharmacist or GP conversation, not a supplement one.

Signs your intake has been low for a while

None of these confirms anything on its own, and several have other explanations entirely. They are reasons to get a blood test, not to self-diagnose.

• Tiredness that does not lift with rest, breathlessness on stairs you used to manage, or unusual pallor.
• Hair shedding more than usual, brittle nails, or skin that has become dry and slow to heal.
• Pins and needles, numbness, or a change in balance, which can relate to B12 and always warrants a GP appointment.
• Mouth ulcers, a sore or smooth tongue, or cracks at the corners of the mouth.
• Muscle cramps, twitches, or feeling weaker than your activity level explains.
• Getting every bug going, and taking longer than usual to shake it off.
• Food tasting bland or metallic.

What to realistically expect

I would rather be honest than encouraging here. If your intake has genuinely been low and you start topping it up, the water-soluble nutrients replenish quickly, within days to a couple of weeks. Iron stores are a different matter: ferritin rebuilds over months, not weeks, and a few weeks of tablets will not undo a year of low intake. Vitamin D takes several weeks to move your blood level meaningfully. And none of it fixes the underlying reason you are not eating. If a small appetite is the root of the problem, supplements buy you insurance while you and your GP work out what is going on, which is a genuinely useful thing for them to do, but it is not the whole job.

A few cautions worth knowing

• Medication interactions are the big one. Iron and calcium interfere with levothyroxine and with several antibiotics. Vitamin K affects warfarin. Magnesium and zinc can bind some antibiotics. If you take any regular medicine, run your list past a pharmacist. It takes five minutes and it is free.
• Pregnancy and breastfeeding. Do not take supplements containing vitamin A in the form of retinol, and follow the UK folic acid and vitamin D advice specifically for pregnancy.
• Kidney disease. Magnesium, potassium and several other minerals are cleared by the kidneys, so doses need to be discussed with your clinician rather than chosen off a shelf.
• Biotin and blood tests. High-dose biotin can interfere with several common laboratory assays, including thyroid and troponin tests. Tell whoever takes your blood what you are taking.
• Haemochromatosis or any condition involving iron loading. Do not take iron unless you have been told to.
• Unintended weight loss. If you are losing weight without trying, please treat that as a medical question first and a nutrition question second.

When to speak to your GP, pharmacist or a dietitian

Book an appointment rather than shopping if any of the following apply: your appetite has dropped and stayed down for more than a few weeks, your weight is falling without you intending it, you have swallowing difficulty or pain when eating, you have numbness or tingling, or you feel breathless and exhausted in a way that is new. A blood test for full blood count, ferritin, B12, folate and vitamin D is straightforward, cheap for the NHS, and turns guesswork into a plan. A pharmacist is the right person for interaction questions and for choosing between products. A registered dietitian is the right person if your diet has narrowed a long way and you need help widening it again.

Frequently asked questions

Is a multivitamin enough if I am barely eating?

For most people it is the right foundation but not the whole answer. A standard multivitamin at close to 100% NRV covers the B group, vitamin C, zinc and a modest amount of iron and vitamin D. What it usually does not carry is enough vitamin D for a British winter, or enough iron if your intake has really collapsed. So: multivitamin first, then look at vitamin D and B12, then iron if it applies to you.

Should I take vitamins on an empty stomach if I cannot face food?

Water-soluble vitamins are fine without food, though some people find them uncomfortable. Fat-soluble vitamins A, D, E and K absorb better with something containing fat, so try to pair them with whatever small thing you can manage, even a spoonful of yoghurt or a little cheese. Iron is the awkward one, since it absorbs best without food but is much easier on the stomach with it. If it makes you feel sick, take it with a small snack and accept slightly less absorption.

Can supplements make up for not eating?

No, and I would not want anyone to read this article and conclude otherwise. Supplements cover vitamins and minerals. They do not provide energy, protein, fibre, essential fats, or the many compounds in real food that we have not finished cataloguing. Think of them as insurance on the micronutrient side while the eating side gets sorted out.

How long does it take to top up after eating badly for months?

It depends entirely on the nutrient. B vitamins and vitamin C respond within days to weeks. Vitamin D blood levels shift over several weeks. Iron stores are the slow one, often taking three to six months of consistent intake to rebuild, which is why people give up too early and conclude iron did nothing.

Is it dangerous to take more than the label says if I am eating very little?

Yes, it can be, and eating little does not create extra headroom. The UK limits on B6, folic acid, vitamin D, zinc, iron and selenium apply regardless of how much you are eating, and a low intake actually makes some of them more relevant, not less, because you are more likely to be stacking several products at once. Add up what your multivitamin, your single-nutrient tablets and any fortified foods contribute before you increase a dose.

Where to start

If you would like the whole nutrient-gap question covered in one order rather than assembled bottle by bottle, our Complete Daily Bundle brings together the six formulas that map most closely onto the gaps described above: vitamin D3 with K2, vitamin B12, magnesium glycinate, zinc with copper, omega-3 and a probiotic. You can also browse everything we have written in one place on our supplement guides hub, or start from the Pure Vitamins UK home page.

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Dr. Miron, Founder of Pure Vitamins UK

Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. This article is for general information and is not medical advice. If you are concerned about your appetite, your weight or your nutrient status, please speak to your GP or pharmacist.