Supplements and energy: which vitamins and minerals have been studied?
Short answer: No supplement simply switches on your energy. If you’re tired because of a deficiency, such as iron deficiency, replenishing it may help, but first have your GP check your levels. In a study of 198 fatigued women with low iron stores, the fatigue score decreased by 47.7% with iron and by 28.8% with a placebo (Vaucher et al., 2012). Caffeine works differently: studies have linked it to temporarily increased alertness, and up to 400 mg per day is considered safe for healthy adults (EFSA, 2015).
Last updated: October 26, 2026 · Written by Florian Fermin
Feeling tired is no fun, and the shelves are full of products promising more energy. What you’re allowed to claim about energy on a label is strictly regulated in the EU, and that’s a good thing. So here’s a summary of what’s been studied, how much you need, and where the limits are. With our supplements for energy and vitality, you can see which claim applies to each product.
Can supplements really give you more energy?
Supplements don’t automatically give you more energy. Fatigue is often related to sleep, stress, exercise, or your health. Only if you’re tired because of a nutrient deficiency, such as iron, can replenishing it make a difference. Caffeine and guarana work differently: they’re used for temporary alertness, but don’t resolve a deficiency.
There are roughly two approaches. The first is temporary alertness through caffeine, for example from coffee, tea, or guarana. The second is replenishing a deficiency with vitamins or minerals that you don’t get enough of through your diet.
These two approaches are often mixed up in advertising. A cup of coffee won’t fix an iron deficiency, and an iron tablet won’t wake you up within an hour.
When is iron useful for fatigue, and how much iron do you need per day?
Iron is particularly useful if you have a confirmed deficiency or low iron stores. According to the Netherlands Nutrition Centre, adult men need 11 mg of iron per day, and women before menopause need 16 mg. EFSA sets a safe level of 40 mg per day for adults, from food and supplements combined.
Iron is a mineral needed to make hemoglobin, the protein in red blood cells that carries oxygen. Ferritin is a measure of your iron stores, which your GP can measure in your blood.
In a Swiss study, 144 women with unexplained fatigue received 80 mg of iron or a placebo for four weeks. Their fatigue decreased by 29%, compared with 13% for the placebo, but only in women with ferritin levels of 50 micrograms per liter or lower (Verdon et al., 2003). A French study of 198 women found a similar pattern after 12 weeks (Vaucher et al., 2012).
Note: 80 mg per day is well above the safe level of 40 mg and should only be taken under a doctor’s supervision. The Netherlands Nutrition Centre advises not taking more than 100% of the recommended amount of iron from a supplement. So I would never take iron on a guess; I’d get a blood test first.
What does vitamin C do for iron absorption?
Vitamin C is often mentioned in connection with the absorption of iron from plant-based foods. This refers to non-heme iron, the type of iron found in vegetables, legumes, and most supplements. According to the Netherlands Nutrition Centre, adults need 75 mg of vitamin C per day, and no tolerable upper limit has been established.
Heme iron is found in meat and fish and is well absorbed. Non-heme iron is less well absorbed. Research found that vitamin C consumed in the same meal was associated with better absorption of non-heme iron (Lynch and Cook, 1980).
You don’t need to take a supplement for that. Vegetables and fruit with your meal, such as bell peppers or kiwi, contain vitamin C. However, more than 2 g of vitamin C per day may cause digestive problems, such as diarrhea (Netherlands Nutrition Centre).
How much magnesium do you need, and what is the upper limit for magnesium supplements?
According to the Netherlands Nutrition Centre, adult men need 350 mg of magnesium per day, and women need 300 mg. There is no upper limit for magnesium from food. If you take a supplement, the tolerable upper limit is 250 mg of magnesium per day from that supplement.
Magnesium is a mineral your body needs for many processes. Most people get it from regular food.
Magnesium is often linked to sleep, and good sleep naturally makes a difference in how fit you feel. A systematic review of 7,582 participants found an association between magnesium status and sleep quality in observational studies. The randomized studies had mixed results (Arab et al., 2022).
What is the difference between caffeine, guarana, and vitamins for fatigue?
Caffeine and guarana are used for temporary alertness; vitamins and minerals can only make up for a deficiency. According to EFSA, up to 400 mg of caffeine per day is safe for healthy adults, with a maximum of 200 mg at a time. For pregnant women, the limit is 200 mg per day from all sources combined.
In a review of studies on caffeine, low to moderate doses of about 40 to 300 mg were associated with improved alertness and reaction time (McLellan et al., 2016). The amount of caffeine in a cup varies by coffee and brewing method.
Guarana is a plant whose seeds naturally contain caffeine. In a meta-analysis of 8 studies with 328 participants, people responded slightly faster after taking guarana, with no difference in accuracy. It’s unknown whether this was due to caffeine or other compounds (Hack et al., 2023). Read more in what guarana is.
What is MCT oil used for?
MCT oil consists of medium-chain triglycerides, fats with shorter chains than most fats in your diet. People mainly use it in coffee, shakes, or as part of a low-carb diet. It’s a fat, not a vitamin or mineral, so it won’t make up for a deficiency.
Read what MCT oil is to find out what research has found about MCT.
Which nutrients and amounts are associated with fatigue, all in one overview?
The table shows the recommended amounts and upper limits for adults, along with research findings. The amounts are from the Netherlands Nutrition Centre and EFSA. When taking a supplement, always check how much you already get from your diet.
| Substance | Recommended daily amount (adults) | Upper limit or safe level | What research has found |
|---|---|---|---|
| Iron | Men 11 mg, women up to menopause 16 mg | 40 mg per day (EFSA, safe level) | Less fatigue in women with low ferritin (Verdon 2003, Vaucher 2012) |
| Vitamin C | 75 mg | No upper limit, digestive issues above 2 g | Improved absorption of non-heme iron (Lynch and Cook, 1980) |
| Magnesium | Men 350 mg, women 300 mg | 250 mg per day from supplements | Association with sleep quality in observational studies, mixed results in trials (Arab 2022) |
| Caffeine | No recommended amount | 400 mg per day, 200 mg at a time (EFSA) | Improved alertness and reaction time at 40-300 mg (McLellan 2016) |
| Guarana | No recommended amount | Count the caffeine | Slightly faster reaction time, no difference in accuracy (Hack 2023) |
When should you have your GP check your fatigue first?
If you’ve been tired for weeks without a clear reason, see your GP before buying supplements. A blood test can, for example, measure your iron stores. That way, you won’t take anything you don’t need or miss an underlying cause.
This is certainly true of iron. Too much iron is not harmless, because excess iron in your body can damage organs (EFSA, 2024). And a deficiency always has a cause that you’ll want to know. To learn more about substances often mentioned for focus, read our article on nootropics.
Summary in 3 points
- Supplements don’t automatically give you energy. Taking a supplement can make a difference only if you have a deficiency, such as low iron stores, and you should get tested first.
- Recommended daily intake for adults: iron 11 to 16 mg, vitamin C 75 mg, magnesium 300 to 350 mg. Upper limits: iron 40 mg, magnesium from supplements 250 mg.
- Caffeine and guarana are used for temporary alertness. EFSA considers 400 mg of caffeine per day safe for healthy adults.
Frequently asked questions
Which vitamin do you need if you’re always tired?
That depends on the cause. Fatigue can be caused by a deficiency, such as iron deficiency, but also by sleep, stress, or your health. So have your GP investigate the cause first before taking anything.
How much iron can you take per day from a supplement?
The Netherlands Nutrition Centre advises taking no more than 100% of the recommended amount from a supplement: 11 mg for men and 16 mg for women before menopause. EFSA considers 40 mg per day safe from all sources combined.
How much magnesium can you take per day from a supplement?
For magnesium from supplements, the tolerable upper intake level is 250 mg per day. Magnesium from regular food does not count toward this limit.
How much caffeine is safe per day?
For healthy adults, EFSA sets a limit of 400 mg per day, with a maximum of 200 mg at a time. For pregnant women, the limit is 200 mg per day.
How soon can you notice an effect from an iron supplement?
The studies measured results after 4 to 12 weeks, and reduced fatigue was seen only in women with low iron stores.
Sources
- Vaucher P, Druais PL, Waldvogel S, Favrat B (2012). Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ, 184(11), 1247-1254. Europe PMC 22777991
- Verdon F, Burnand B, Stubi CLF, et al. (2003). Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ, 326(7399), 1124. Europe PMC 12763985
- EFSA Panel on Nutrition, Novel Foods and Food Allergens (2024). Scientific opinion on the tolerable upper intake level for iron. EFSA Journal, 22(6), e8819. Europe PMC 38868106
- Lynch SR, Cook JD (1980). Interaction of vitamin C and iron. Annals of the New York Academy of Sciences, 355, 32-44. Europe PMC 6940487
- Arab A, Rafie N, Amani R, Shirani F (2022). The Role of Magnesium in Sleep Health: a Systematic Review of Available Literature. Biological Trace Element Research, 201(1), 121-128. Europe PMC 35184264
- McLellan TM, Caldwell JA, Lieberman HR (2016). A review of caffeine's effects on cognitive, physical and occupational performance. Neuroscience and Biobehavioral Reviews, 71, 294-312. Europe PMC 27612937
- Hack B, Penna EM, Talik T, Chandrashekhar R, Millard-Stafford M (2023). Effect of Guarana (Paullinia cupana) on Cognitive Performance: A Systematic Review and Meta-Analysis. Nutrients, 15(2), 434. Europe PMC 36678305
- EFSA (2015). Caffeine. Topic page and scientific advice on the safety of caffeine, May 27, 2015. efsa.europa.eu, accessed October 26, 2026.
- Netherlands Nutrition Centre. Encyclopedia: iron, magnesium and vitamin C, accessed October 26, 2026.
This article is for informational purposes and is not medical advice. Dietary supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. If in doubt, during pregnancy, or when taking medication, consult your doctor or pharmacist.
