Tired all the time? Causes and the nutrients that play a role

Most of us have spells when it feels as if our batteries are flat. In a survey in Germany, 31% of people over 16 said they sometimes or often have signs of fatigue². Women are affected more often than men². If it turns into constant tiredness, though, it’s worth taking a closer look.

Causes of tiredness: what’s behind it?

In GPs’ experience, the most common reasons for tiredness that goes on for a long time are to do with lifestyle and emotional wellbeing¹. These include worries at work or at home, too little exercise and disturbed sleep¹. If you’re not very active, it’s easy to fall into a vicious circle: you lose strength, everyday activities get harder, and the tiredness grows¹.

Depression and anxiety disorders often come with tiredness². Other causes include pauses in breathing at night (sleep apnoea), side effects of medicines, alcohol and the after-effects of infections². In one review, only about 3% of people who saw their GP because of tiredness turned out to have anaemia².

Some medicines cause tiredness, for example certain blood pressure or allergy medicines¹. So tell your GP about everything you take, including anything you’ve bought over the counter. But don’t stop taking any medicine without talking to your doctor first¹.

Constantly tired despite plenty of sleep: what could be the reason?

Spending a long time in bed doesn’t mean you’re sleeping well. Broken sleep, including sleep disrupted by breathing problems, can be both a cause of tiredness and a symptom that comes with it¹. Alcohol in the evening and sleeping tablets can make your sleep less restful¹. So mention it to your GP if you snore loudly, stop breathing briefly during sleep or nod off during the day without meaning to².

When should you have your blood tested?

If tiredness lasts more than four weeks and there’s no known cause, the German guideline for GPs considers some blood tests useful². These include blood sugar, a full blood count, a marker of inflammation, liver function tests and a thyroid test (TSH)². In women of childbearing age, ferritin (the protein that stores iron) can also be measured². Further tests are done if what you tell your GP, or their examination of you, points to something specific².

Vitamin B12 and vitamin D aren’t part of this basic list². Whether a test makes sense depends on your situation. Older people and vegetarians, for example, have a higher risk of vitamin B12 deficiency⁴. The Deutsche Gesellschaft für Ernährung (the German Nutrition Society) recommends measuring vitamin D when there’s good reason to suspect a deficiency, or in people in at-risk groups⁵.

Which nutrients play a role in tiredness?

For some nutrients, there’s an authorised health claim relating to tiredness. Iron, vitamin B12, vitamin C, folate, niacin, pantothenic acid, riboflavin and vitamin B6 contribute to the reduction of tiredness and fatigue, and magnesium contributes to a reduction of tiredness and fatigue³. A supplement makes sense mainly when your intake really is low. The safest way to find out is to talk to your GP.

Iron

One study included 198 tired women aged 18 to 53 who were still having periods, with ferritin below 50 µg/l and no anaemia⁶. On 80 mg of iron a day, their fatigue score fell by 48% over twelve weeks, compared with 29% on placebo⁶. The German GP guideline is more cautious: it finds a clear benefit mainly when iron stores are markedly depleted².

So take iron only once a blood test has shown that you need it. An iron supplement can then help top up your iron intake. When it’s best to take iron is explained in our article on when to take iron: morning, evening or with a meal.

Vitamin B12

Vitamin B12 contributes to the reduction of tiredness and fatigue and to normal energy-yielding metabolism³. A deficiency can develop over years, and tiredness is one of the possible signs⁴. Older people, people with gastrointestinal conditions and vegetarians are affected more often⁴. If you’d like to top up your intake, a vitamin B12 supplement is one way to do it.

Magnesium

Magnesium contributes to a reduction of tiredness and fatigue, to normal energy-yielding metabolism and to normal muscle function³. As a supplement, magnesium in capsules is one option. How the different forms of magnesium compare is explained in our article on which magnesium is right for you.

Vitamin D

There’s no authorised health claim for vitamin D in relation to tiredness. Its authorised health claims include that vitamin D contributes to the maintenance of normal muscle function and to the normal function of the immune system³. Almost 60% of people in Germany don’t reach the desirable blood level of 50 nmol/l⁵. In later life, the skin makes considerably less vitamin D than it did when you were younger⁵.

When it comes to tiredness, the studies are inconsistent. In one study of 120 tired adults with low vitamin D levels, four weeks after a single high dose, the fatigue score had fallen further than with placebo⁷. But the participants were only 29 years old on average. The German GP guideline finds no link between low vitamin D and increased tiredness².

Don’t take more than the recommended daily amount. If you take any medicines, check with your doctor before starting any food supplement.

What helps with tiredness in everyday life?

The guideline recommends a step-by-step approach that starts from what you can manage at the moment¹. Physical activity pitched at the right level for you has proven effective, and so has behavioural therapy, for a range of causes¹. The aim is a better balance between activity and rest¹. Results don’t usually come overnight¹.

There’s one important exception. If you feel worse for a long time after physical or mental exertion, a separate illness may be behind it: ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome)¹. In that case, more exercise won’t help and can do harm. Talk to a doctor about it before you increase your activity¹.

Frequently asked questions about constant tiredness