Micronutrients for Lifters
Macros get the attention and micronutrients cause the problems. Four are worth checking, and iron is the one most often both deficient and over-supplemented.
Last updated: 1 July 2026
Overview
Macronutrients decide whether you grow. Micronutrients decide whether the machinery works while you try.
Most people who train do not need a cupboard of supplements. Four nutrients are worth knowing your position on, because deficiency in any of them is common, has real training consequences, and is easy to miss.
Quick Answer
The micronutrients most often short in a training diet are iron, vitamin D, B12 and calcium. NHS guidance sets iron at 8.7mg a day for men and women over 50, and 14.8mg a day for women aged 19 to 49.
Key Points
- Iron requirement is nearly twice as high for women aged 19 to 49.
- Iron is the one to test before supplementing, not after.
- Vitamin D is hard to get from food at UK latitudes in winter.
- B12 is a non-negotiable supplement on a fully plant-based diet.
- More is not better. Several of these are harmful in excess.
Iron
Iron carries oxygen. Being short of it shows up as fatigue, breathlessness and poor endurance long before anything dramatic happens, which is exactly why it gets mistaken for being unfit or under-slept.
NHS figures for daily need:
| Group | Daily iron |
|---|---|
| Men 19 and over | 8.7mg |
| Women 19 to 49 | 14.8mg |
| Women 50 and over | 8.7mg |
The gap between 14.8 and 8.7 is menstrual blood loss, and it is why iron deficiency is far more common in women of reproductive age. Endurance athletes of any sex are also at higher risk.
Do not supplement iron on a hunch. NHS guidance is that doses above 20mg a day can cause constipation, nausea, vomiting and stomach pain, and that very high doses can be fatal, particularly for children. Supplements of 17mg a day or less are said to be unlikely to cause harm.
Iron overload is a genuine condition and the body has no good way to excrete excess. If you suspect deficiency, ask for a blood test rather than guessing.
Food sources per NHS guidance include liver, red meat, beans such as kidney beans, edamame and chickpeas, nuts, dried apricots, fortified breakfast cereals and soy bean flour.
Vitamin D
The one nearly everyone in the UK is short of for part of the year, because it is made in skin from sunlight and there is not enough of it between about October and March.
It matters for bone health and muscle function, and low levels are associated with reduced muscle strength. Food sources are limited: oily fish, egg yolks and fortified products.
Public health advice in the UK is to consider a daily supplement during autumn and winter. It is cheap, well tolerated, and one of the few supplements with a clear case behind it.
B12
Found almost exclusively in animal foods. A vegan diet without supplementation or fortified foods will run short eventually, and deficiency causes neurological damage that is not always reversible.
This is the one nutrient on this page where supplementing is not optional for the group at risk. See [plant-based nutrition](/wiki/articles/plant-based-nutrition).
Calcium
Bone is built by loading it and supplied by eating calcium. Resistance training does the first job; dairy, fortified plant milks, tinned fish with bones and dark greens do the second.
It matters most for people who avoid dairy without replacing it, and around and after menopause, when bone loss accelerates.
Who is most at risk
| Group | Watch |
|---|---|
| Women 19 to 49 | Iron |
| Vegans | B12, iron, calcium, omega 3 |
| Vegetarians | Iron, B12 |
| Anyone in the UK, Oct to Mar | Vitamin D |
| Endurance athletes | Iron |
| Long or aggressive dieters | Everything, through low total intake |
| People avoiding dairy | Calcium |
That last row is the general principle: the main cause of micronutrient shortfall in people who train is not an exotic requirement, it is eating too little food overall or eating a very narrow range of it.
Do you need a multivitamin
It is inexpensive insurance if your diet is restricted, monotonous, or in a long deficit. It is not necessary for someone eating a varied diet with plenty of vegetables, fruit and whole foods.
What a multivitamin does not do is fix a diet. It covers small gaps; it does not substitute for the food.
Common Mistakes
| Mistake | Why it causes problems | Better approach |
|---|---|---|
| Supplementing iron without testing | Excess is harmful and hard to shed | Get a blood test first |
| Assuming fatigue is under-training | Iron deficiency looks identical | Rule it out |
| Skipping vitamin D in winter | Sunlight is insufficient at UK latitudes | Supplement Oct to Mar |
| Vegan without B12 | Risk of irreversible harm | Supplement, no exceptions |
| Megadosing anything | Several are toxic in excess | Stay near the stated amounts |
Frequently Asked Questions
How much iron do I need a day?
NHS guidance is 8.7mg for men and for women over 50, and 14.8mg for women aged 19 to 49.
Should I take an iron supplement?
Not without evidence you are low. Excess iron is harmful, and a blood test settles it.
Do I need vitamin D?
In the UK, a daily supplement through autumn and winter is the standard advice, because sunlight is not sufficient to make enough at these latitudes.
Will a multivitamin improve my training?
Only if it fills a real gap. It does nothing for someone already eating a varied diet, and it does not compensate for eating too little.
Sources
NHS guidance on iron - https://www.nhs.uk/conditions/vitamins-and-minerals/iron/
NHS guidance on vitamin D - https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
NHS vitamins and minerals overview - https://www.nhs.uk/conditions/vitamins-and-minerals/
British Nutrition Foundation - https://www.nutrition.org.uk/