Updated by Dr Francesca Haarer BSc, PG Cert (Med Ed), BMBS, MRCS and Dr Kate Smith BSc, MBChB 

Updated date May 2025

We live in a fast-paced world, and finding time to rest can be challenging. It’s no wonder that feeling fatigued and lacking energy is common among many of us, including women.

If you've been feeling noticeably tired and can't figure out why, it's essential to rule out pregnancy first. It's common to feel very tired or even exhausted during pregnancy. This is because your hormones are changing dramatically, and can leave you craving a nap.

However, if you’re confident you’re not pregnant, let’s dive into 6 of the other most likely reasons you’re feeling a regular slump in energy. We’ll cover thyroid dysfunction, low iron levels, type 2 diabetes, and vitamin deficiencies.

You can also take H&B&Me’s Energy blood test, which tests for all 6 potential causes we discuss below, and gets you doctor-reviewed results within 48 hours.

1. Underactive thyroid

An underactive thyroid is a common health issue that can cause low energy in women.¹ The thyroid gland produces thyroid hormone, which regulates your metabolism (the body’s process of converting food and drink into energy).¹

An underactive thyroid, also known as hypothyroidism, can lead to various symptoms, including fatigue, weight gain, and depression.¹ Hypothyroidism is more common in females than males.¹ You can take our Energy blood test to learn more about your thyroid function.

2. Low iron levels

Low iron levels are a major culprit for tiredness in females and are commonly characterised by fatigue, shortness of breath and paler skin.² Iron is essential for producing healthy red blood cells that carry oxygen throughout your body without trouble.³

A lack of iron can lead to iron deficiency anaemia, which women are particularly susceptible to due to blood loss during menstruation.³

You can understand your iron levels by using a reliable test,⁴ and having it interpreted by  a doctor before you start any iron replacement.

It's important to note that the cause of iron deficiency anaemia needs to be worked out so you can get the  right diagnosis and treatment. ² There are more serious causes of low iron levels, so it's important to see a doctor to assess any signs or symptoms of low iron.

3. Type 2 diabetes

Type 2 diabetes is a serious health condition that causes your blood sugar to become too high.⁵ It’s where your body can’t make enough insulin or the insulin it produces doesn’t work as it should, which is different from type 1 diabetes.⁶ Type 1 diabetes is a condition where your body isn’t able to make any insulin because your own immune system has destroyed the cells that make insulin (an autoimmune condition).⁶

If type 2 diabetes isn’t recognised and treated quickly, it can cause serious damage to your organs, your blood vessels and even your eyesight.⁷ 

Feeling tired all the time is one of the main symptoms of diabetes. Other signs of the condition include feeling unusually thirsty, losing weight without meaning to, blurred vision, and needing to pee more often than usual.⁸ 

Being overweight and not doing exercise is a common risk factor for diabetes, so it’s important to try and stay within a healthy weight range and to stay active.⁸ Having high blood pressure can also be a risk factor, along with your family history of type 2 diabetes.⁸ You can check if you may be at risk for diabetes with this blood test.

4. Vitamin D deficiency

Vitamin D contributes to the maintenance of normal bones, muscle function and teeth as well as the normal function of the immune system.⁹ It's known as 'the sunshine vitamin' because sun exposure is the main way your body produces it.

Not many foods provide your body with enough vitamin D, so supplementation is recommended by the NHS during the winter months.⁹ For some it is recommended to consider a vitamin D all year round - for example if you don’t get outside much, wear high-coverage clothing or have brown or black skin.

Being deficient in vitamin D is linked with low energy levels in some people.¹⁰ On top of that, there’s even a correlation between low vitamin D and sleep disorders, which could mean less rest, lower sleep quality or general sleepiness.¹¹

The good news is that if you're low in vitamin D, supplementation may make you feel less tired if you are deficient in vitamin D.¹⁰

5. Vitamin B12 deficiency

Unlike vitamin D, vitamin B12 is naturally found in many foods. However, these are mainly animal foods, like meat, fish, and dairy, so you're at higher risk of vitamin B12 deficiency if you eat a vegan diet.¹²

Tiredness and low energy are two main symptoms of vitamin B12 deficiency,¹³ alongside a red, sore tongue, breathlessness, vision issues, headaches, and sensory disturbances like pins and needles.

Like iron, vitamin B12 contributes to normal red blood cell formation.¹⁴ Red blood cells carry oxygen around your body, so if they're not working correctly, your body doesn’t get the oxygen it needs.¹⁵ This can lead to anaemia (where either there aren’t enough red blood cells or they aren’t working properly), and it can make you feel pretty exhausted.¹⁶ To get insights into your vitamin B12 levels, you can take H&B&Me's Energy blood test.

6. Folate deficiency

Folate, also known as vitamin B9, has similar functions to B12 and therefore similar symptoms if you don’t have enough of either.¹⁷ Folate  contributes to the reduction of tiredness and fatigue and the normal function of the immune system.¹⁷,¹⁸ It also contributes to normal blood formation, normal psychological function and to maternal tissue growth during pregnancy.¹⁹

Folate is common in many foods, like leafy green vegetables, peas and chickpeas.¹⁴
However, your body doesn’t store folate on a long term basis, so your levels can drop if you’re not regularly getting enough folate in your diet.¹⁴ So if you’ve neglected to eat  a healthy, balanced diet recently and feel relentlessly tired, you might be at risk of a folate deficiency.

On top of tiredness, other folate deficiency symptoms include mouth ulcers, muscle weakness, and shortness of breath. ¹³ Folate levels are one of the biomarkers measured in our Energy blood test.

Finally, if you're pregnant, the NHS recommends you take 400 micrograms of daily folic acid (the supplement form of folate) from before pregnancy until 12 weeks into your pregnancy.²⁰ They recommend this so there’s a reduced risk of developmental problems for the baby (or babies) in those early weeks of pregnancy.²⁰

The final word

Low energy levels and unusual tiredness in females can be due to many reasons, such as pregnancy, an underactive thyroid, low iron levels, type 2 diabetes, and deficiencies in vitamins D, B12, and folate.

It's essential to uncover the root cause of your fatigue so you can effectively and safely address it. H&B&Me's Energy blood test offers a simple, quick, way to assess for some of the underlying reasons of low energy.

With doctor-reviewed results for all six of the most common causes of tiredness in females outlined in this article available within 48 hours, you may find the reason behind your energy slump to potentially help you  bring back your zest for life.

An important reminder: low energy and tiredness can be related to other serious conditions not discussed in this article. H&B&Me's energy test does test for some important conditions related to tiredness, but not all of them. If you have persistent, unexplained tiredness for more than 4 weeks, you are advised to see your GP.

References

1. NHS. Underactive thyroid (hypothyroidism) [Internet]. NHS. 2021. Available from: https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/ 

2. NHS. Iron Deficiency Anaemia [Internet]. NHS. 2024. Available from: https://www.nhs.uk/conditions/iron-deficiency-anaemia/ 

3. NHS. Iron [Internet]. NHS. NHS; 2020. Available from: https://www.nhs.uk/conditions/vitamins-and-minerals/iron/ 

4. The Clinical and Biological Manifestations in Women with Iron Deficiency Without Anemia Compared to Iron Deficiency Anemia in a General Internal Medicine Setting: A Retrospective Cohort Study

https://www.dovepress.com/the-clinical-and-biological-manifestations-in-women-with-iron-deficien-peer-reviewed-fulltext-article-IJGM

5. NHS. What Is Type 2 diabetes? [Internet]. nhs.uk. 2025. Available from: https://www.nhs.uk/conditions/type-2-diabetes/what-is-type-2-diabetes/

6. Diabetes UK. Differences between Type 1 and Type 2 diabetes [Internet]. Diabetes UK. 2024. Available from: https://www.diabetes.org.uk/diabetes-the-basics/differences-between-type-1-and-type-2-diabetes 

7. NHS. Type 2 diabetes [Internet]. nhs.uk. 2017. Available from: https://www.nhs.uk/conditions/type-2-diabetes/complications/ 

8. NHS. Symptoms - type 2 diabetes [Internet]. NHS. 2025. Available from: https://www.nhs.uk/conditions/type-2-diabetes/symptoms/

9. NHS. Vitamin D - Vitamins and Minerals [Internet]. NHS. 2020. Available from: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d 

10. Effect of vitamin D3 on self-perceived fatigue https://journals.lww.com/md-journal/Fulltext/2016/12300/Effect_of_vitamin_D3_on_self_perceived_fatigue__A.2.aspx

11. The Association between Vitamin D Deficiency and Sleep Disorders: A Systematic Review and Meta-Analysis

https://www.mdpi.com/2072-6643/10/10/1395

12. NHS. The vegan diet [Internet]. nhs.uk. 2022. Available from: https://www.nhs.uk/live-well/eat-well/how-to-eat-a-balanced-diet/the-vegan-diet/ 

13. NHS Choices. Symptoms - vitamin B12 or folate deficiency anaemia [Internet]. NHS. 2019. Available from: https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/symptoms/ 

14. NHS. B Vitamins and Folic Acid - Vitamins and Minerals [Internet]. NHS. 2020. Available from: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/ 

15. NHS Blood and Transplant. Functions of blood: Transport around the Body [Internet]. NHS Blood Donation. 2022. Available from: https://www.blood.co.uk/news-and-campaigns/the-donor/latest-stories/functions-of-blood-transport-around-the-body/

16. World Health Organization. Anaemia [Internet]. www.who.int. World Health Organisation; 2024. Available from: https://www.who.int/health-topics/anaemia#tab=tab_1 

17. NHS . Vitamin B12 or folate deficiency anaemia [Internet]. NHS. 2023. Available from: https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/ 

18. Mikkelsen K, Apostolopoulos V. Vitamin B12, Folic Acid, and the Immune System. Nutrition and Immunity. 2019;103–14.

19. Folate: foods, functions, how much do you need & more [Internet]. www.eufic.org. 2021. Available from: https://www.eufic.org/en/vitamins-and-minerals/article/folate-foods-functions-how-much-do-you-need-more

20. NHS. Vitamins, minerals and supplements in pregnancy [Internet]. nhs.uk. NHS; 2020. Available from: https://www.nhs.uk/pregnancy/keeping-well/vitamins-supplements-and-nutrition/