Which vitamin for fatigue: what iron, vitamin D and B12 do and do not explain

In this article you will read which vitamin plays a role in fatigue, which vitamin and mineral deficiencies go with tiredness, what studies with iron, vitamin D and vitamin B12 found, and when a blood test makes sense. That matters, because fatigue comes from many more things than a deficiency. If you are tired and have no other symptoms, a blood test rarely finds a cause.⁠⁴ The BioProfile energy scan measures how much your fatigue bothers you and shows where you stand today. The scan is not a diagnosis. The scan gives you insight to make better choices about your diet and lifestyle. Only a doctor can identify a cause.

Which vitamin for fatigue: which deficiency goes with it

Thuisarts lists what usually causes tiredness:

• stress, grief or money worries
• worrying, anxiety or depression
• little exercise, an unhealthy diet, smoking or alcohol
• illnesses such as flu, COVID-19, diabetes, thyroid problems and heart conditions
• unwanted side effects of medicines.⁠⁴

Food is only one line on that list.

Two deficiencies are known causes of fatigue. With too little iron, you may tire quickly, look pale, get out of breath easily and have restless legs.⁠⁵ A B12 deficiency leads to a form of anaemia that can cause tiredness, dizziness, palpitations and ringing in the ears. This kind of deficiency is uncommon.⁠⁶ Vitamin D has also been tested for fatigue, in people with a low level.⁠²

In plain words: a deficiency is one possible cause among many others. If your energy dips mainly after lunch, read why your energy dips after lunch.

Iron status: where most of the studies are

One study followed 198 menstruating women aged 18 to 53 with unexplained fatigue. All of them had low iron stores, and none had anaemia. For 12 weeks they took 80 mg of iron or a placebo every day. With iron, fatigue fell by 47.7 per cent, and with the placebo by 28.8 per cent. Iron made no measurable difference to quality of life, depression or anxiety.⁠⁷ A review of six similar studies found the same pattern. In tired people with an iron deficiency but no anaemia, iron reduced fatigue slightly more than a placebo did.⁠¹

What this means for you: if a blood test shows too little iron, even without anaemia, extra iron can make you slightly less tired. The placebo groups also felt better, so not all of the change came from the iron.

Women in their fertile years can get too little iron more easily, because blood is lost during menstruation. For this group the Voedingscentrum advises 16 mg of iron a day. For men, and for women after the menopause, the advice is 11 mg. True iron deficiency with anaemia is rare in the Netherlands. Iron supplements are not recommended without a medical reason, and only a blood test through your GP can show whether you have a deficiency.⁠⁵

Vitamin D: one study in people with a low level

In a double-blind study, 120 tired but otherwise healthy adults with low vitamin D were given either a single dose of 100,000 units of vitamin D3 or a placebo. Their average age was 29. Four weeks later, 72 per cent of the vitamin D group felt less tired. In the placebo group, it was 50 per cent.⁠²

What this means for you: in people who were tired and had little vitamin D, a dose made a noticeable difference within a month. It was a single study, and it says nothing about people with a normal vitamin D level.

Separately from fatigue, the Voedingscentrum advises an extra 10 micrograms of vitamin D a day for a number of groups. These are children up to 3, women aged 50 to 69, and people aged 4 to 69 who have dark skin or get little sun. Everyone aged 70 and over is advised to take 20 micrograms a day.⁠⁸

Vitamin B12: important if you have a deficiency

If you get too little B12, it often takes a few months or even a year before you notice. Three groups are most at risk: people who eat no animal products, people whose bodies absorb B12 poorly, and older adults. Vegans are advised to take a supplement of 2.8 micrograms a day.⁠⁶ Nobody knows whether extra B12 helps against fatigue if you are not deficient. A review of 16 studies found only one that measured unexplained fatigue, and that is too little to draw a conclusion.⁠³

In plain words: B12 matters if you are deficient in it. If you are not deficient, there is no evidence that a B12 supplement gives you more energy.

Fatigue in Crohn’s disease

Of adults with Crohn’s disease or ulcerative colitis, 47 per cent live with fatigue. That rises to 72 per cent when the disease is active, and in remission it is still 47 per cent. The factors most strongly linked to the fatigue were disturbed sleep, anxiety, depression and anaemia.⁠⁹

What this means for you: fatigue is common in Crohn’s disease, even in remission. Sleep, mood and anaemia are the points to discuss with your doctor.

When to see your GP

Contact your GP if your fatigue lasts longer than a month. Also contact your GP if other symptoms come along with it:

• heavy sweating at night
• less appetite
• changes in your bowel movements
• shortness of breath
• being very thirsty and needing to wee often
• heart palpitations
• feeling very low or very tense.⁠⁴

What the energy scan measures

The energy scan asks five questions about the past two weeks and turns your answers into an energy score. The score shows how much fatigue you are carrying and gives you a baseline to compare against later. A questionnaire cannot measure blood values such as iron, vitamin D or B12, and it cannot find the cause of your fatigue. Finding the cause is a job for a doctor.

In summary

Fatigue has many causes, and a deficiency is only one of them.⁠⁴ Iron has been studied the most, and iron helps a little in tired people with an iron deficiency.⁠¹ In one study, vitamin D made a difference in people with a low level.⁠² For B12, there is too little research on fatigue to say anything.⁠³ A blood test through your GP shows whether you have too little iron,⁠⁵ and the energy scan shows how much fatigue you are carrying today.