Why am I always tired? Seven hidden causes of fatigue in women over 40

Persistent fatigue in women over forty often stems from seven specific, treatable underlying conditions including perimenopause, iron deficiency, thyroid dysfunction, sleep apnoea, vitamin deficiencies, dehydration, and chronic stress.

In this article, Dr Izie Allison-Omoruyi, a GP and lifestyle medicine physician, goes into expert detail. 

What are the hormonal factors causing exhaustion?

Perimenopause is the leading cause of energy loss as fluctuating oestrogen and progesterone directly disrupt sleep cycles and metabolic function. The decline in oestrogen reduces mitochondrial efficiency, creating a constant feeling of heaviness even after restful nights. Rising cortisol levels during this transition fragment deep REM sleep, preventing true restoration for 85 per cent of women in this age group.

Thyroid dysfunction represents the second hidden cause, where an underactive gland slows the body's entire metabolism. This hypothyroid state forces the heart to work harder to maintain body temperature, leaving patients with chronic lethargy and cold sensitivity. Blood tests measuring TSH and free T4 are essential to rule out this silent contributor before attributing symptoms simply to ageing or stress.

Which nutritional and physical deficits drain energy?

Iron deficiency anaemia acts as the third major culprit, particularly for women experiencing heavier menstrual periods during perimenopause. Low ferritin levels deprive red blood cells of oxygen, meaning muscles cannot generate enough power for daily tasks, resulting in early fatigue. Vitamin B12 and D deficiencies form the fourth and fifth causes respectively, as low B12 impairs nerve function while insufficient Vitamin D leads to muscle weakness and persistent low mood.

Dehydration often functions as the sixth hidden cause, especially when fluid intake drops due to reduced thirst mechanisms in older adults. Even mild dehydration thickens the blood, making it harder for the heart to pump oxygen to tissues. Finally, chronic stress creates a seventh cause by keeping the nervous system in a constant "fight or flight" mode, which depletes adrenal reserves and prevents the body from entering recovery states.

• Iron stores below thirty micrograms per litre correlate directly with severe fatigue scores.
• Vitamin D levels under twenty nanograms per millilitre are linked to significant muscle weakness.
• Sleep apnoea risks increase significantly after forty due to weight gain and hormonal shifts.
• Magnesium insufficiency impairs energy production at the cellular level within mitochondria.

Standard blood screens sometimes miss borderline deficiencies, requiring a detailed nutritional assessment to uncover these root causes. Supplementation should only follow confirmed results to avoid masking other underlying health issues.

References

1. National Institute for Health and Care Excellence. Menopause: diagnosis and management. NICE Guideline NG23. Updated 2024.
2. British Thyroid Foundation. Understanding Hypothyroidism and Symptoms. 2023.
3. British Dietetic Association. Food Fact Sheet: Iron. 2023.
4. Royal College of Physicians. Fatigue in adults: assessment and management. Clinical Guidelines, 2022.
5. British Sleep Society. Guidelines for the Management of Insomnia and Fatigue. 2023.