Why Am I Tired All the Time? 10 Causes and Blood Tests

Feeling tired all the time is one of the most common reasons people see a GP. Sometimes the cause is simple, such as too little sleep or a demanding few months. Sometimes it is a treatable medical problem, such as low iron or an underactive thyroid. The good news is that most causes can be found and improved.

This guide covers the most common reasons for constant tiredness, the blood tests that help find a cause, what you can change yourself, and when to see a doctor.

Quick answer

If you are tired all the time, the cause is usually everyday: too little or poor quality sleep, stress, alcohol, caffeine or too little activity. Common medical causes include iron deficiency anaemia, an underactive thyroid, low vitamin D or B12, diabetes, depression and sleep apnoea. If tiredness lasts more than four weeks, or comes with weight loss, breathlessness or night sweats, see a GP, who may suggest blood tests.

Everyday causes of tiredness

• Not enough sleep, or poor quality sleep: most adults need seven to nine hours. Late screens, shift work, noise and young children all chip away at this.
• Stress and a busy life: long-term stress keeps the body on alert and is draining even when you are sitting still.
• Alcohol and caffeine: both disrupt deep sleep, even when you fall asleep easily.
• Too little activity: it sounds backwards, but inactivity makes most people more tired, and regular movement increases energy.
• Irregular eating: skipping meals and relying on sugary snacks causes energy dips.

Emotional causes

Low mood, depression and anxiety very often show up as tiredness, poor sleep and a lack of motivation. If you have lost interest in things you usually enjoy, or feel worried most of the time, speak to your GP.

Medical causes

• Iron deficiency anaemia: particularly common in women with heavy periods, and in pregnancy. Breathlessness and feeling cold are other signs.
• Underactive thyroid: tiredness with weight gain, feeling cold, constipation and dry skin.
• Low vitamin D, B12 or folate: common in the UK, especially in winter or with a plant-based diet.
• Diabetes: tiredness with thirst, passing more urine or blurred vision.
• Coeliac disease: tiredness with bloating, diarrhoea or low iron.
• Sleep apnoea: loud snoring, pauses in breathing and waking unrefreshed.
• After a viral illness: tiredness can last for weeks after flu or Covid.
• Perimenopause and menopause: night sweats and broken sleep often cause daytime fatigue.
• Medicines: some blood pressure tablets, antihistamines and antidepressants can cause tiredness.
• ME/CFS: long-term exhaustion that worsens after activity and is not relieved by rest.

Why am I tired all the time as a woman?

Women are more likely to have low iron because of periods and pregnancy, and more likely to have thyroid problems. Hormonal changes around periods, after pregnancy and in the perimenopause also affect sleep and energy. Caring responsibilities add to the load. Checking iron stores and thyroid function is a sensible first step.

Why am I so tired in pregnancy?

Feeling tired, or even exhausted, is very common in pregnancy, especially in the first 12 weeks, when hormonal changes can leave you feeling tired, sick and emotional. Energy often improves in the middle of pregnancy and then dips again in the final weeks as sleep becomes harder. Anaemia is common in pregnancy and can add to tiredness, which is why iron levels are checked at antenatal appointments. Rest when you can, eat regular meals and keep gently active. Tell your midwife or GP if you feel exhausted, breathless, dizzy or very low.

Blood tests that help find a cause

• Full blood count and ferritin for anaemia and iron stores
• Thyroid function
• Vitamin D, B12 and folate
• HbA1c for blood sugar and diabetes
• Liver and kidney function
• Coeliac screening if you have gut symptoms
• Inflammation markers if you also have aches or feel unwell

Tired all the time and gaining weight

Tiredness with weight gain is a common combination. An underactive thyroid is a classic cause, often with feeling cold, constipation and dry skin; see underactive thyroid symptoms. Other possibilities include poor sleep and sleep apnoea, low mood, the perimenopause, being less active, and some medicines. Useful blood tests include thyroid function, HbA1c for blood sugar, and a full blood count. If you snore loudly or wake gasping, mention this to your GP as well.

What you can do now

• Keep a regular bedtime and wake time, even at weekends
• Stop screens 30 to 60 minutes before bed
• Cut caffeine after midday and reduce alcohol
• Walk every day, ideally in daylight
• Eat regular meals with protein and whole foods
• Keep a two-week energy and sleep diary to spot patterns

When to see a GP

• Tiredness has lasted more than four weeks without an obvious reason
• You have lost weight without trying
• You have night sweats, fevers or new lumps
• You are breathless, or your periods are very heavy
• You notice blood in your stools or a change in bowel habit
• You feel low, hopeless or anxious most of the time

Frequently asked questions

Why am I tired even after sleeping well?

Sleep may be less restful than it seems, for example with sleep apnoea, or the cause may be something else, such as low iron, thyroid problems or low mood. Blood tests are a good starting point.

Can low vitamin D make you tired?

Yes. Low vitamin D is common in the UK and can cause tiredness and aches. The NHS advises considering a daily vitamin D supplement in autumn and winter.

Is being tired all the time a sign of something serious?

Usually not, but tiredness with weight loss, night sweats, lumps or breathlessness should always be checked promptly.

How long should I wait before seeing a doctor?

If tiredness has lasted about four weeks and simple changes have not helped, book an appointment.

Fatigue assessment and blood tests in Chiswick

Omnia Lifestyle offers blood tests for tiredness and a practitioner review of the results at our clinic in Chiswick, W4. Results can be shared with your GP.

• Blood tests for tiredness in Chiswick: no GP referral needed, and the blood draw usually takes under ten minutes. Individual tests include vitamin B12, iron and ferritin, full blood count, thyroid, vitamin D and HbA1c.
• Tired All The Time health check: 43 biomarkers in one test, with an Omnia practitioner going through the results with you and a written report to share with your GP.

Omnia Lifestyle is at 8 to 9 Bedford Corner, The Avenue, Chiswick W4 1LZ, close to Turnham Green station, on bus routes 94, E3 and 272. Limited parking is available on request when booking.

Read more about fatigue, thyroid disorders and poor sleep, explore blood tests, or book an appointment.

This article is general information, not medical advice. If you have any of the warning signs listed above, see your GP.