5 reasons you could be tired all the time

Are your energy levels at an all-time low? Here are five reasons that could be causing your fatigue.

Feeling tired all the time is one of the most common reasons why people visit their doctor [1]. But sometimes finding out the underlying cause of low energy levels can be a long process of elimination. 

Although lack of sleep is not the only cause of feeling tired, not getting enough quality sleep can be detrimental to your health and cause several symptoms. 

Symptoms of lack of sleep include: 

  • Fatigue 
  • Weakened immune system 
  • Weight gain 
  • Cognitive impairment/brain fog 

You can read more about the risks of not getting enough sleep in our sleep - the best medicine? blog. 

Lack of sleep isn’t the only reason for low energy levels. Many people are left feeling exhausted even when they have had a good night’s sleep. 

If this is the case, it can be difficult to know whether you are simply doing too much or if your low energy levels are a symptom of an underlying health condition.  

So, if you’ve ever asked yourself “why do I feel tired all the time?”. Work through these five common causes of fatigue. 

What could be causing my constant tiredness?

There are a few things that could be a cause of your tiredness, these include:

Could low iron be causing my fatigue?

Iron is required for several bodily processes, including [2]: 

  • Creating new red blood cells 
  • Carrying oxygen around the body 
  • Strengthening the immune system 

Low levels of iron can lead to a decrease in the amount of oxygen carried around the body, resulting in iron deficiency anaemia – one of the most common causes of anaemia. 

Symptoms of anaemia include [3]: 

  • Fatigue 
  • Heart palpitations (noticeable heartbeats) 
  • Dizziness 
  • Headaches 

To reduce your risk of anaemia, it is recommended to increase your iron intake through diet and, in some cases, consider supplementation. 

Anaemia can be common and is easily detected through a simple blood test. You can measure your iron levels from the comfort of your own home with our Iron Blood Test

iron blood test product banner

Could diabetes be causing my low fatigue?

People who are prediabetic or have diabetes often experience fatigue because their blood sugar is too high or, if they are on medication, too low [4]. 

Diabetes is currently one of the biggest health issues in the UK and can cause several symptoms. 

Symptoms of diabetes include [5]

  • Frequent urination 
  • Extreme thirst 
  • Unexplained weight loss 
  • Fatigue 

For many, diabetes can go undetected for years. Our Diabetes (HbA1C) Blood Test is a simple finger-prick test that you can do from the comfort of your own home. Within your results, you’ll get advice from a qualified doctor on your next steps. 

Should your symptoms persist, or if you are worried about your symptoms, then seek medical care. 

In some cases, diabetes can be prevented with some simple lifestyle changes. Read more in 10 ways to reduce your risk of type 2 diabetes

diabetesblood test product banner

Could a thyroid condition be a cause of my fatigue?

The thyroid is responsible for producing key hormones which affect almost every cell in the body. The two main thyroid hormones are thyroxine (T4) and triiodothyronine (T3) [6]. 

A thyroid condition can mean your thyroid will either be underactive or overactive. 

An underactive thyroid (hypothyroidism) occurs when the gland does not produce enough of the thyroid hormones causing several symptoms. 

Symptoms of an underactive thyroid include [7]: 

  • Fatigue 
  • Sensitivity to the cold 
  • Weight gain 
  • Constipation 
  • Depression 
  • Loss of libido (sex drive) 

An overactive thyroid (hyperthyroidism) occurs when the thyroid makes too much T4 and T3 and can cause several symptoms. 

Symptoms of an overactive thyroid include [8]: 

  • Fatigue 
  • Nervousness, anxiety, and irritability 
  • Mood swings 
  • Difficulty sleeping 
  • Sensitivity to heat 
  • Weight loss 

Thyroid conditions are common and found in about 2% of the UK population [9]. If you are experiencing symptoms of a thyroid condition, then one of our tests can help you determine whether it is your thyroid or something else. 

You can read more about our thyroid tests in our Thyroid test buying guide. 

thyroid collection blood test product banner

Is low vitamin B12 causing me to feel tired all the time?

One of the most important nutrient groups to give you an energy boost is the B vitamins, as many are directly involved in creating energy at a cellular level. 

Key biological processes B12 is used in include [10]: 

  • Tissue and cell repair 
  • Energy production 
  • Red blood cell production 
  • Functioning of nerves and DNA 

vitamin b12 blood test product banner

Your body absorbs B12 from the foods you eat. 

The best food sources of B12 include: 

  • Dairy products 
  • Meat 
  • Fish 

If you eat a plant-based diet, there are other sources that you can get B12 from, including tofu and fortified plant milk. You can read more in our blog: plant-based diets and nutrition

Low levels of vitamin B12 can cause red blood cells to enlarge, affecting their oxygen-carrying capacity. 

Symptoms of B12 deficiency include [11]: 

  • Fatigue 
  • Dizziness 
  • Feeling faint 
  • Persistent headaches 

You can check to see if you are deficient in B12 with our simple at-home Vitamin B12 Blood Test.

Knowing whether you are deficient in B12 means that with simple lifestyle changes (and sometimes medical intervention if a medical condition is causing malabsorption) you can help alleviate symptoms. 

Is low vitamin D causing my fatigue?

Vitamin D (commonly referred to as the sunshine vitamin) is important for maintaining healthy teeth, muscles, and bones. 

When you are exposed to the sun, the body creates vitamin D using nutrients obtained from certain foods. 

Foods that contain vitamin D include [12]: 

  • Oily fish 
  • Red meat 
  • Liver 
  • Egg yolks 
  • Fortified cereals 

In the UK, from the end of September to late March, it is recommended to take a vitamin D supplement. If you do not get enough vitamin D, you can become deficient. 

Around 20% of adults in the UK are deficient in vitamin D [13]

Symptoms of vitamin D deficiency include: 

  • Fatigue 
  • Muscle weakness 
  • Mood swings 

You can check to see if you are deficient in vitamin D with our simple finger-prick Vitamin D Blood Test from the comfort of your own home. 

With simple lifestyle changes, your vitamin D levels can be improved.  

Lifestyle changes to improve vitamin D levels include: 

  • Getting out in the sun more 
  • Eating more vitamin D-rich food 
  • Taking vitamin D supplements 

You can read more about vitamin D and vitamin D deficiency in our vitamin D guide. 

vitamin d blood test product banner

How can I get to the bottom of me feeling tired all the time?

Investigating your health from your own home has never been easier. With our quick and convenient service, you can have your health check results delivered online within just a few days. 

If you need help choosing the right test, then try our test finder or see our health and wellness buying guide. 

There are many causes of feeling tired, which aren’t all mentioned in this article. If you are feeling tired all the time or persistently fatigued, discuss this with your doctor so they can investigate the root cause.


  1. UK. 2021. Sleep and tiredness. [online] Available at: <https://www.nhs.uk/live-well/sleep-and-tiredness/> [Accessed 21 December 2021]. 
  2. Abbaspour N, Hurrell R, Kelishadi R. Review on iron and its importance for human health. J Res Med Sci. 2014 Feb;19(2):164-74. PMID: 24778671; PMCID: PMC3999603. 
  3. UK. 2021. Iron deficiency anaemia. [online] Available at: <https://www.nhs.uk/conditions/iron-deficiency-anaemia/> [Accessed 21 December 2021]. 
  4. Rasch B, Born J. About sleep's role in memory. Physiol Rev. 2013 Apr;93(2):681-766. doi: 10.1152/physrev.00032.2012. PMID: 23589831; PMCID: PMC3768102. 
  5. UK. 2021. Diabetes. [online] Available at: <https://www.nhs.uk/conditions/diabetes/> [Accessed 21 December 2021]. 
  6. Shahid MA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. [Updated 2021 May 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK500006/ 
  7. UK. 2021. Underactive thyroid (hypothyroidism) - Symptoms. [online] Available at: <https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/symptoms/> [Accessed 21 December 2021]. 
  8. UK. 2021. Overactive thyroid (hyperthyroidism). [online] Available at: <https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/> [Accessed 21 December 2021]. 
  9. Ingoe, L., Phipps, N., Armstrong, G., Rajagopal, A., Kamali, F. and Razvi, S., 2017. Prevalence of treated hypothyroidism in the community: Analysis from general practices in North-East England with implications for the United Kingdom. Clinical Endocrinology, 87(6), pp.860-864. 
  10. od.nih.gov. 2021. Office of Dietary Supplements - Vitamin B12. [online] Available at: <https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/> [Accessed 21 December 2021]. 
  11. UK. 2021. Vitamin B12 or folate deficiency anaemia. [online] Available at: <https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/> [Accessed 21 December 2021]. 
  12. UK. 2021. Vitamin D. [online] Available at: <https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/> [Accessed 21 December 2021]. 
  13. Crowe, F., Jolly, K., MacArthur, C., Manaseki-Holland, S., Gittoes, N., Hewison, M., Scragg, R. and Nirantharakumar, K., 2019. Trends in the incidence of testing for vitamin D deficiency in primary care in the UK: a retrospective analysis of The Health Improvement Network (THIN), 2005–2015. BMJ Open, 9(6), p.e028355. 

Related tests