How Do I Know Which Supplements I Actually Need?

Most people buy supplements the wrong way round, and I include a younger version of myself in that. You hear someone on a podcast rattle off their morning stack, it sounds impressive, and a week later there are eleven tubs on the kitchen counter and no real idea which of them is doing anything. We've written about a couple of those famous stacks ourselves, so I'm not throwing stones.

So the better way in is to start from a gap rather than a product. For most people the gaps come from three places: where you live, your stage of life and the way you eat, and what your blood results actually say. Goals like sleep, focus and energy come after that, as a second layer. Get the order right and you'll usually end up buying less, and getting more out of what you do buy.

Start with where you live

If you live in Ireland, vitamin D is the closest thing to a universal answer. Our skin can only make it from roughly late March to late September, and for the rest of the year we're relying on food and supplements. The largest study of vitamin D status in older Irish adults, run by TILDA at Trinity College Dublin, found that one in eight people over 50 were deficient, rising to one in four in winter. The striking part is the comparison the researchers drew: Finland, which is further north and gets less sun than we do, has a deficiency rate under 1%, largely because of a national policy of fortification and supplementation (Trinity College Dublin, 2017).

That study looked at over-50s, so younger readers shouldn't assume the same numbers apply to them. But the sunlight problem is the same for everyone on this island, and from about October to March most adults here have a reasonable case for a daily vitamin D supplement. Ours is Vitamin D3 3,000iu, and there's more on the winter side of things in our honest guide to immune season.

Then your stage of life and what you eat

This is where things get personal, and where a few needs are well established enough that nobody serious argues about them.

If you're trying for a baby or could become pregnant, the HSE advises a daily folic acid supplement. We don't stock a standalone folic acid, and you don't need a specialist shop for it anyway, any pharmacy will have it for a few euro.

If you eat a fully plant-based diet, vitamin B12 is the one to sort out, because there's next to none of it in plant foods. Plenty of people eat that way and do well on it, provided they supplement or eat fortified foods without fail. The same vitamin is worth keeping an eye on as you get older, since the body tends to absorb B12 from food less efficiently with age. You'll find B12 and the other single vitamins in our Vitamins & Minerals range.

If you have heavy periods, or you're coming into menopause and feeling flattened, iron may be part of the picture, but this is the one nutrient I'd never take on a hunch. Too much iron is harmful for both women and men (trust me, I know - I have hemochromatosis!), and the only way to know whether you're low is a blood test.

And if you train hard, protein and creatine are the two with the strongest case behind them, with creatine carrying an EU-authorised claim for physical performance in short bursts of high-intensity exercise at 3g a day. The creatine guide covers it, whoever you are.

Get your bloods done

If you only take one thing from this post, make it this. Your GP can test for vitamin D, B12, folate and ferritin (the measure of your iron stores), and if the waiting list is long there are private tests available. A blood result turns "I think I might need" into "I know I need", and it gives you a baseline to retest against in a few months, which is the only reliable way to know whether a supplement is doing its job.

It can save you money too. If the reason you've been flat for months turns out to be low iron or low B12, no energy supplement on any shelf was going to fix it, and a blood test would have told you as much in about a week.

Then, and only then, your goals

Once the basics are covered, the second layer is about what you want more of: better sleep, steadier focus, more resilience when life gets busy. This is where most of our range lives, and it's a perfectly reasonable place to spend money, as long as you're honest with yourself about which column a product sits in.

I'll use myself as the example. I take Brain & Body Creatine most days, mostly because it keeps the afternoon brain fog away for me, and MagTech at night because I sleep deeply on it. Neither of those is in my "need" column. They're in my "I like how I feel on them" column, and I think that distinction matters, because it stops you treating every new product as essential.

If sleep is your thing, start with magnesium and sleep. If it's focus, Do Nootropics Actually Work? is the honest version. If you've been running on stress for months, What Stress Takes From Your Body covers the nutrients that tend to get used up along the way.

What about a multivitamin?

A multivitamin is a reasonable insurance policy if your diet is patchy, and there's no harm in one for most people. But it's worth knowing what it isn't. In 2022 the US Preventive Services Task Force reviewed the evidence and concluded there wasn't enough of it to say whether multivitamins help prevent heart disease or cancer in healthy adults, and it advised against beta-carotene and vitamin E supplements for that purpose (JAMA, 2022). That review looked at disease prevention rather than everyday wellbeing, but it's a useful corrective to the idea that a daily multi is doing heavy lifting. The other thing to watch is overlap: a multi plus a few targeted products can easily double your intake of something like zinc without you noticing.

How to tell if it's working

Add one thing at a time. Give it six to eight weeks, which is long enough for most nutrients to make a difference you'd notice, and jot down how you're sleeping, how your energy holds up in the afternoon, whatever it was you were hoping to change. For anything you had tested, retest after about three months. If you can't tell any difference and there was no gap to fill in the first place, that's an answer too, and a cheap one.

When you do buy, buy from someone who'll tell you what's in the tub and in what amounts. Our red flags guide covers what to check before you pay. Everything we stock ships from Dublin, the same day if you order by 4pm.

So there you have it: a supplement shop telling you to buy fewer supplements!

Frequently asked questions

Do I need supplements if I eat a healthy diet?

Often not many. A varied diet covers most nutrients for most people, but vitamin D is the usual exception in Ireland from October to March, and certain life stages and diets, such as pregnancy or a plant-based diet, bring specific needs of their own.

Should everyone in Ireland take vitamin D?

Most adults here have a good case for it through the winter months, because the sun is too weak to make vitamin D in the skin from roughly late September to late March. If you're unsure of your levels, your GP can test them.

Can my GP test me for deficiencies?

Yes. A GP can arrange blood tests for vitamin D, B12, folate and ferritin, which is the measure of your iron stores. Private testing is also available if you'd rather not wait.

Is a multivitamin enough?

It can be a sensible safety net for a patchy diet, but the doses of individual nutrients are often modest, and a 2022 review found insufficient evidence that multivitamins prevent heart disease or cancer. If a blood test shows a specific shortfall, a targeted supplement usually makes more sense.

How long before I know if a supplement is working?

Give most supplements six to eight weeks, add one at a time so you can tell what's doing what, and retest anything you had measured after around three months.

This article is for general information only and is not medical advice. If you are pregnant, breastfeeding, taking medication or managing a health condition, speak to your GP or pharmacist before starting any supplement.