Start with vitamin D. If you live in the UK, the NHS advises everyone to consider 10 micrograms a day through autumn and winter. After that, the most common shortfalls are magnesium, vitamin E, vitamin A and vitamin C. Calcium too if you skip dairy. B12 moves up the list if you're vegan or getting older. Everything else depends on what you eat.
That answer is less exciting than the supplement aisle wants it to be. The aisle sells 40 single bottles. The data points at a handful of gaps, and they're the same gaps for most people.
The short version
- Vitamin D first, at least October to March. NHS: 10mcg a day.
- Magnesium, vitamins E, A and C are the common US shortfalls.
- Vegan or getting older? Add B12 to the list.
- Fix the diet first, then fill what's left with one product.
- Skip megadoses. Trials don't support them for disease prevention.
What vitamins should I take? Look at where people actually fall short
The best answer to "what vitamins should I take" comes from intake data, not from marketing. The cleanest dataset is a 2011 analysis in the Journal of Nutrition that used NHANES 2003-2006 data from 16,110 Americans to compare what people take in (food, fortified food and supplements combined) against the estimated average requirement, the intake level that covers half of healthy people. The authors declared no conflicts of interest.
Most nutrients came out fine. For vitamin B6, folate and zinc, 8% of people fell below the average requirement. For B12, thiamin, riboflavin, niacin, copper and selenium it was under 6%. A small group of nutrients looked very different.
| Nutrient | Below the average requirement (food plus supplements) | Main food sources |
| Vitamin D | 70% | Oily fish, egg yolks, fortified foods |
| Vitamin E | 60% | Nuts, seeds, vegetable oils |
| Magnesium | 45% | Nuts, seeds, beans, whole grains, leafy greens |
| Calcium | 38% | Dairy, tinned fish with bones, fortified foods |
| Vitamin A | 34% | Liver, eggs, dairy, orange and dark green veg |
| Vitamin C | 25% | Peppers, citrus, kiwi, broccoli |
Potassium was the outlier. Only 3% of people reached the adequate intake, though potassium comes mostly from food (potatoes, beans, fruit, veg), and multivitamins carry only a small fraction of a day's worth. Calcium is mostly a dairy question. If you eat dairy most days you are probably covered, and if you don't, it needs a look.
Those figures include people already taking supplements. Strip supplements out and the gaps get wider. A newer NHANES analysis of 26,282 US adults from 2005-2016 put inadequate intake at 95% for vitamin D, 84% for vitamin E, 46% for vitamin C and 45% for vitamin A. Worth knowing: that paper's authors work for a supplement company, so lean on the older, independent numbers if you want the conservative view. Both point the same way.
For more on how this breaks down for men specifically, see the nutrient deficiency map.
Why the answer changes from person to person
A shortfall in a national survey tells you where the risk sits. It doesn't tell you about your plate. A few things move you up or down the list.
Where you live and when. Between October and early March, the NHS says the UK sun is not strong enough for your skin to make the vitamin D you need. From late March to September most people make enough outdoors. So in the UK, vitamin D is a seasonal question with a fixed answer for half the year.
What you eat. Someone who eats oily fish twice a week, a handful of nuts most days and two or three portions of veg is in a different position from someone living on chicken, rice and protein shakes. The second diet is common among men who train, and it's light on exactly the nutrients in the table above.
Your age and your diet type. Vitamin B12 is the clearest example. A diet with meat, fish and dairy usually provides enough B12, according to the NHS, while vegans who don't take a supplement or eat fortified foods are at risk. Age matters too. A 2004 review in the Canadian Medical Association Journal found B12 deficiency in more than 20% of elderly people, and in over 60% of cases the cause was food-cobalamin malabsorption: the body struggles to release B12 from food, even when the diet contains plenty. That's why B12 comes up for older men even if they eat meat. We cover the early signs in B12 deficiency symptoms.
What to do, in order
- Fix the obvious food gaps first. The NHS recommends at least 2 portions of fish a week, one of them oily. Add nuts or seeds daily, beans a few times a week and coloured veg at most meals, and you cover a lot of the table above with food alone.
- Take vitamin D from October to March at minimum. The NHS says 10 micrograms (400 IU) a day is enough for most people and warns against going above 100 micrograms (4,000 IU) a day. If you're indoors most of the year, consider it year-round.
- If you're vegan, add B12. The NHS vegan diet guidance also flags vitamin D, iodine, selenium and calcium as harder to get.
- Cover the remaining gaps with one product instead of six. Magnesium, vitamins A, C and E, and a sensible spread of the rest can sit in a single daily serving. Six separate bottles mostly add cost and the risk of doubling up.
- Get a blood test if something feels off. Vitamin D and B12 are easy to measure, and a result beats guessing.
If you're trying to work out what a decent all-in-one should contain, this breakdown of what a multivitamin should contain goes nutrient by nutrient.
What you probably don't need
Filling a shortfall and chasing disease prevention are two different jobs. The second one has a poor track record.
In 2022 the US Preventive Services Task Force reviewed the trials and concluded that vitamin E supplements give no net benefit for preventing heart disease or cancer, that the harms of beta carotene supplements outweigh the benefits for the same purpose, and that the evidence on multivitamins for preventing either is insufficient. The same statement notes that 52% of US adults use at least one supplement and 31% take a multivitamin, most often for general health and to fill dietary gaps.
So vitamin E shows up in two places in this post, and both are true. Most people fall short of the average requirement from diet, and taking big doses to prevent heart disease doesn't work. Covering the gap is a reasonable goal. Megadosing for protection isn't. We went through the trial evidence in more detail in are multivitamins worth it.
The same logic rules out most single-nutrient megadoses sold on a "more is better" pitch. If you aren't short of something, extra doesn't add a benefit, and for fat-soluble vitamins like D, the upper limits exist for a reason.
When to see a doctor
Supplements are for covering dietary gaps. They aren't a fix for symptoms you haven't explained. If you have ongoing tiredness, pins and needles, numbness, mouth ulcers or unexplained weight loss, see your GP and ask for bloods before you start buying bottles. The same goes if you take prescription medication, since some vitamins interact with drugs. The best-known example: the NHS says not to take vitamin K supplements while on warfarin. Fireblood contains vitamin K, so the same applies to us.
The short answer, again
Vitamin D through the dark months. Then look honestly at your diet for magnesium, vitamin E, vitamin A and vitamin C, and add B12 if you're vegan or getting older. That covers most men. The shelf of 40 bottles covers mostly the shop's margins.
We built Fireblood to cover those gaps in one scoop: vitamin D3 at 50mcg (2,000 IU), magnesium at 100mg, vitamin E at 45mg, vitamin A at 900mcg as retinyl palmitate (no beta carotene), vitamin C at 500mg and B12 at 2.5mcg as methylcobalamin, alongside 33 other ingredients. The 100mg of magnesium is a top-up, so keep the nuts and seeds. It won't replace a decent diet, and it isn't meant to. See the full formula here.
Photo: Pexels.
