Constant tiredness is one of the most common reasons women see a doctor. Here are the usual causes, the blood tests worth asking about and when fatigue needs prompt care.
The short answer
Most ongoing tiredness has a common, fixable cause: not enough sleep or poor-quality sleep, stress, low iron, low vitamin B12 or D, an underactive thyroid, depression or anxiety, or a medicine side effect. If you have felt exhausted for more than a few weeks despite reasonable sleep, it is worth seeing a doctor and asking about simple blood tests.
Iron deficiency: the big one for women
Heavy periods, pregnancy, breastfeeding and plant-based diets all raise the risk of low iron. Iron stores (ferritin) can run low before haemoglobin drops, so you can feel tired, breathless on stairs, or notice hair shedding, brittle nails, restless legs or ice cravings even before you are anaemic. Ask for a full blood count and ferritin. If iron is low, your doctor will look for the cause and suggest supplements, usually for at least three months. Don’t take high-dose iron without testing, as too much is harmful.
Other common medical causes
- Underactive thyroid: tiredness, feeling cold, weight gain, constipation, dry skin. A TSH blood test checks it.
- Low vitamin B12 or folate: more common with vegan diets, metformin, acid-reducing medicines or gut conditions.
- Low vitamin D: common in Canadian winters.
- Blood sugar problems: prediabetes or diabetes can cause fatigue, thirst and frequent urination.
- Sleep apnoea: loud snoring, gasping, morning headaches and daytime sleepiness; more common after menopause.
- Pregnancy and perimenopause: both commonly cause fatigue.
- Depression and anxiety: low energy is often a main symptom.
The short version
Blood tests to ask about
- Complete blood count and ferritin
- TSH (thyroid)
- Vitamin B12, and folate if relevant
- HbA1c or fasting glucose
- Vitamin D only if you are at risk
- Pregnancy test if possible
Your doctor will decide which tests suit your symptoms and history.
Everyday habits that help
- Aim for 7 to 9 hours in bed at consistent times
- Eat regular meals with protein and iron-rich foods, plus vitamin C to help absorb plant iron
- Move every day, even a 10-minute walk
- Limit alcohol and late caffeine
When to see a doctor promptly
Book soon if tiredness comes with unexplained weight loss, fever or night sweats, heavy or unusual bleeding, shortness of breath or chest pain, low mood or thoughts of self-harm, or if it lasts more than a few weeks.
Frequently asked questions
What blood tests should I ask for if I am always tired?
Commonly a full blood count, ferritin (iron stores), thyroid TSH, vitamin B12 and blood sugar. Your doctor will tailor them to you.
Can low iron make you tired without anaemia?
Yes. Low ferritin can cause fatigue, hair shedding and breathlessness before haemoglobin falls into the anaemic range.
Why am I tired before my period?
Hormone shifts can disturb sleep and mood in the days before a period. Heavy periods can also lower iron over time.
Should I take iron supplements for tiredness?
Only after a blood test shows low iron. Too much iron can be harmful.
Track your energy
If your tiredness comes with cycle changes, hot flushes or poor sleep in your 40s, the free Menopause Starter Kit includes a simple symptom tracker to take to your appointment.
