Updated: Nov 26, 2020

Do you feel tired all the time? Do you drift through most days in a sluggish state – despite having a full night’s sleep? Unfortunately, fatigue is multi-factorial which can make it hard to track down the exact cause and is not always easy to determine.

Fatigue is a common problem involving a physical and mental state of being extremely tired.

This article will discuss some common causes of fatigue- to help understand why you might be constantly feeling so tired.


Chronic stress may have a profound effect on your energy levels and overall quality of life. Although some stress is normal, excessive levels of stress have been linked to fatigue.

When the body is exposed to stress, it releases cortisol (stress hormone) from the adrenal glands. Normally, when a stressor goes away, the release of cortisol reduces. However, in the modern world, many of us are constantly activating our body to release cortisol as we are often stressed.

When we’re exposed to chronic stressors over a long period of time, our adrenals pump out more and more cortisol as we become more and more resistant to its effects. The negative feedback cycles that normally keep things in check get turned off, and our health suffers as a result. Eventually, our bodies cannot keep up with the demand for cortisol, and cortisol levels become low (1) which can ultimately cause fatigue.

Although cortisol is the body’s primary stress hormone for modulating the body’s daily and long-term responses to stress, cortisol is not the only hormone related to stress. DHEA, the other major hormone released from the adrenal glands, helps balance cortisol, especially when cortisol levels get too high. An individual who has more DHEA than cortisol seems to experience fewer negative effects from the same stressors than a person who has a lower ratio of DHEA to cortisol.

What can you do?

  • Start a mind-body activity practice like being present in prayer, meditation, yoga or journaling to reduce mental and emotional stress. The benefits of implementing a stress management practice grow over time, so the sooner you start, the better!

  • Do not go too long without eating. If you’re worried about your stress levels, I’d caution against skipping breakfast (or any meal, actually) on a regular basis. Getting a high protein breakfast in the morning stabilises your blood sugar levels throughout the day, which in turn helps to reduce stress on your body.


Your energy levels are determined by what you eat because your body converts the fats, proteins, and carbohydrates you eat into daily energy. Therefore, if your diet is less than ideal, it could be a cause of constant fatigue.

1. A diet filled with refined simple carbohydrates

A diet filled with refined simple carbohydrates such as white pasta, white bread, sugary desserts, and sweetened fizzy drinks and fruit juices, can all contribute to fatigue.

Refined simple carbohydrates can cause a rapid spike in blood sugar levels, which leads to a surge of insulin to move sugar out of the blood and into the cells, followed by a drop in blood sugar levels – all of which can leave you feeling tired and fatigued.

2. Not eating enough

Eating a well-balanced diet including plenty of colourful vegetables, moderate amounts of fruit, lean protein, and sources of healthy fats like olive oil and fish is also crucial as you could be deficient in essential nutrients, which is another common cause of fatigue.

Common deficiencies linked to fatigue include vitamin B12, folate, iron, and zinc.

In addition, when you are not eating enough, your metabolism slows down in order to conserve energy, potentially causing fatigue.

What can you do?

  • Limit refined simple carbohydrates and focus on whole grain fibrous carbohydrates such as oats, sweet potatoes, quinoa, brown, red and wild rice, bulgur wheat, freekah, whole barley, rye and spelt.

  • When you do eat carbohydrates, combine them with protein and healthy fat to slow absorption and stabilise your blood sugar.

  • Eat a well-balanced meal containing healthy fats, protein and complex carbohydrates with plenty of colour vegetables.

  • Limit caffeinated beverages as it can trick your body into thinking that you have more energy available than you actually do.


Good quality sleep is essential. Sleep affects almost every type of tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Inadequate or poor-quality sleep is a common cause of fatigue. Getting several hours of uninterrupted sleep allows your body and brain to recharge, allowing you to feel energised during the day.

What can you do?

  • Go to bed at roughly the same time every night will create consistency which can improve the quality and duration of your sleep as our bodies become accustomed to schedule.

  • Develop a ‘winding down’ routine before bedtime by dimming the lights in your house and reduce blue or full-spectrum light in your environment by shutting off all electronics 1 or 2 hours before sleep.

  • Adopt relaxation techniques before bed. Proven methods include prayer, deep breathing exercises, meditation, a hot bath or keeping a gratitude journal.

  • Get plenty of activity during the day (no later than 2 to 3 hours before going to bed as performing it too late in the day may cause sleep problems due to the stimulatory effect of exercise, which increases alertness and hormones like adrenaline)


Iron deficiency anaemia is a common cause for feeling weak and tired. In fact, it is the most common nutritional deficiency in the world (2). It is caused by a lack of iron, one of the key nutrients needed to produce healthy blood. Without enough iron, your body cannot produce enough haemoglobin, the important substance found in red blood cells that enables them to carry oxygen throughout the body. Therefore, less oxygen reaches your tissues and muscles, depriving them of energy.

Vitamin B12 is also involved in the formation of red blood cells and helps to support healthy cognitive function and mood - as a result, fatigue is often the most prevalent symptoms of a vitamin B12 deficiency. In addition, vitamin B12 is needed to convert folic acid into its active form so it can be utilised by your body – for this reason, low levels of vitamin B12 are often associated with low levels of folic acid.

Low levels of vitamin D can also cause fatigue that has a severe negative effect on quality of life (7,8,9).

What can you do?

If you think you may have a nutritional deficiency, you can speak to your GP to test your levels. A simple blood test can confirm if you have a deficiency. Afterward, you can then easily increase your nutrient intake, through your diet or with a supplement, if your healthcare practitioner recommends.


The thyroid gland affects virtually every organ in the body. The thyroid produces hormones that regulate every bodily process – even in governing physiological energy demands (6).

The two main hormones made by the thyroid gland are T3 (triiodothyronine) and T4 (thyroxine).

The production of these two hormones is regulated by another hormone, TSH (thyroid-stimulating hormone), which is produced in the brain.

Various factors can cause your thyroid to make either too much T3 or T4 (hyperthyroidism) or too little T3 and T4 (hypothyroidism) – and either extreme can cause fatigue and other issues.

What can you do?

A reliable way to determine if the thyroid gland is the cause of your fatigue is by testing the thyroid’s key hormones – TSH, free T3, T4 and sometimes even testing thyroid antibodies such as TPO and TG to determine if it’s a thyroid issue or an immune system issue.


Neglecting water intake can lead to fatigue. According to the National Hydration Council, symptoms such as tiredness and fatigue make up around 20% of GP visits and it’s estimated that of these visits, dehydration is the cause of 1 in 10 (3).

Studies show that even mild dehydration (1-3% of body weight) can impair many aspects of brain function, concentration, and fatigue (4, 5).

What can you do?

The NHS recommends drinking 1.5 and 2 litres of water a day but this amount can fluctuate depending on a number of factors: How much exercise are you doing? Have you suffered from a bout of diarrhoea or sickness? Are you in a hot, tropical climate? Therefore, there are a few variables to consider, in general, though, we should try to adhere to the 1.5 – 2L rule, more or less.


Some antidepressants, anti-hypertensives, statins, steroids, antihistamines, medication withdrawal, sedatives, and anti-anxiety drugs can cause fatigue. In addition changes in doses or stopping medications can also be a cause.

Bottom line:

The problem with fatigue is that it’s such a non-specific symptom; it has numerous potential causes, and often requires a lot of investigation to determine the primary cause and driver. If you are concerned about feeling tired all the time, I would recommend that you speak to your healthcare practitioner because there may be other underlying issues or health concerns that may need addressing.



1) Robert-Paul Juster, Shireen Sindi, Marie-France Marin et al. (2011). A clinical allostatic load index is associated with burnout symptoms and hypocortisolemic profiles in healthy workers. Psychoneuroendocrinology. 36:6:797-805.

2) World Health Organisation. Micronutrient deficiencies. Available from: https://www.who.int/nutrition/topics/ida/en/

3) National hydration council. 2015. Available from: https://www.naturalhydrationcouncil.org.uk/press/gps-reveal-uk-tired-all-the-time/

4) Armstrong LE, Ganio MS et al. (2012). Mild dehydration affects mood in healthy young women. J Nutr. 142(2):382-8.

5) Ganio MS, Armstrong LE, Casa DJ, McDermott BP, Lee EC. (2011). Mild dehydration impairs cognitive performance and mood of men. Br J Nutr. 106(10):1535-43.

6) Medici M, Visser WE, Visser TJ, Peeters RP. (2015). Genetic determination of the hypothalamic-pituitary-thyroid axis: where do we stand? Endocr Rev. 36(2):214-44.

7) Johnson K, Sattari M. (2015). Vitamin D deficiency and fatigue: an unusual presentation. Springerplus. 7;4:584.

8) Roy, S., Sherman, A., Monari-Sparks, M. J., Schweiker, O., & Hunter, K. (2014). Correction of Low Vitamin D Improves Fatigue: Effect of Correction of Low Vitamin D in Fatigue Study (EViDiF Study). North American journal of medical sciences, 6(8), 396–402.

9) Ecemis GC1, Atmaca A. (2013). Quality of life is impaired not only in vitamin D deficient but also in vitamin D-insufficient pre-menopausal women. J Endocrinol Invest. 36(8):622-7.