5 medical causes of low mood

Did you know that some medical conditions can either cause or mimic low mood?

Sometimes life can get you down, and feeling low is completely normal. However, if you've been feeling low for longer than two consecutive weeks, it’s best to speak to your doctor as it can be a sign of depression. There are many causes of low mood, from stress to overworking yourself – but sometimes a medical condition could be to blame.  

In this blog we discuss five medical causes of low mood:  

  1. Diabetes  
  2. An underactive thyroid 
  3. Gut autoimmune conditions  
  4. A hormone imbalance 
  5. Vitamin deficiencies 

1. Diabetes

Did you know you are twice as likely to have depression if you have diabetes [1]? Diabetes can be exhausting and overwhelming – tie that in with the tiredness you are most likely feeling, and it can be difficult to keep your spirits high.

What’s the link between diabetes and depression?  

Diabetes and low mood can become a vicious cycle, as to take care of one condition, you have to keep on top of the other. Though diabetes does not directly cause depression, the nature of the symptoms and living with the condition can be a factor in developing it [1]. 

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Some data shows that people whose blood sugar levels vary a lot are more likely to have low mood than people with more stable blood sugar levels [2], though more studies are needed to confirm this link. It’s one of many reasons why good glycaemic control is so important in diabetes.

Where to get support  

Whether you think your low mood is caused by undiagnosed diabetes or you have diabetes and are feeling low, your first port of call should be your doctor. 

There are also charities and other services that can help, either through supporting resources, support groups, or helplines, including: 

Try our Diabetes (HbA1c) Blood Test to either measure your risk of type 2 diabetes or to check how well your body is controlling glucose levels. 

2. An underactive thyroid

An underactive thyroid (hypothyroidism) can affect anyone, but it’s five to ten times more common in women than in men [3]. It is commonly diagnosed between the ages of 20 and 40, and the symptoms can often overlap with several other common conditions. 

What’s the link between a thyroid condition and depression? 

Both an underactive and overactive thyroid can affect your mental health.

Thyroid conditions also cause low mood indirectly, either through the of having the condition or due to medication side effects. Medications such as beta blockers can cause you to feel tired, depressed, and experience brain fog [4].  

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Where to get support  

Once your thyroid disorder has started to stabilise, your mental health should improve. But if your symptoms do not improve with treatment, you should speak to your doctor.  

Other places to get support for a thyroid condition include: 

Whether you are investigating a thyroid condition or have already been diagnosed, take a look at our Thyroid Blood Test Buying Guide to see if one of our Thyroid Blood Tests can help you along your thyroid journey. 

3. A gut autoimmune disease

An autoimmune disease is where the immune system attacks the body (as it mistakes its own cells for foreign ones). There are several autoimmune diseases, thyroid being one. But the main three gut autoimmune conditions are coeliac disease, Crohn’s disease, and ulcerative colitis.  

What’s the link between a gut autoimmune disease and depression? 

Gut health and mental health often go hand in hand. Evidence shows that poor gut health can play a part in mood disorders. Likewise, your emotional state may cause digestive symptoms. It's thought to be down to the gut-brain axis, the two-way communication between the brain and the gut via the vagus nerve. 

Because of this link, it’s not surprising that people diagnosed with inflammatory bowel disease (such as Crohn’s or ulcerative colitis) are at a significantly higher risk for depression [5]. And people with coeliac disease are also at increased risk of anxiety, depression, and fatigue, both before and after diagnosis [6].  

Coeliac, Crohn’s disease, and ulcerative colitis can all go undiagnosed for long periods as the symptoms can mimic several other common conditions. If you are experiencing any symptoms or think one of these conditions could be the cause of your low mood, speak to your doctor.  

Where to get support  

Speaking to your doctor, dietitian, or IBD nurse should be your first point of contact if you are feeling low. But there are other great charities that can provide support, such as: 

4. A hormone imbalance

Hormones fluctuate regularly — take a look at the menstrual cycle, for example. Or the way cortisol rises and falls throughout the day. Hormone levels have an impact on our mood, and if they fall out of balance, they can cause unwanted symptoms.  

As well as physical symptoms, a hormone imbalance may cause: 

  • Anxiety  
  • Nervousness  
  • Stress  
  • Depression 

Some hormones have a larger impact on mood than others.  

Hormones involved in mood regulation include: 

  • Oestrogen 
  • Progesterone  
  • Testosterone  
  • Thyroid 
  • Cortisol  
  • Insulin  
  • DHEA  

This means too much or too little of one of these hormones can affect both your physical and mental health.  

If you are concerned about a hormone imbalance or are experiencing any new symptoms, speak to your GP.  

You can also check in on your health with one of our comprehensive blood tests. If you’re not sure which blood test is best, take a look at our Health and Wellness Buying Guide.  

5. Vitamin deficiencies

Vitamin D and vitamin B12 deficiencies are two of the most common vitamin deficiencies in the UK. 

Around one in six adults in the UK has a vitamin D deficiency [7].  And common symptoms include tiredness, low mood, and brain fog. That means if your vitamin D levels are low, something as simple as a vitamin D supplement could lift your spirits. 

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Not quite as common is vitamin B12 deficiency, which affects around 6% of adults in the UK [8].  

Certain conditions and lifestyles may put you at higher risk of developing a B12 deficiency. Gut autoimmune diseases can affect your ability to absorb micronutrients and therefore put you at higher risk, and some diets, such as vegan and vegetarian diets, may also increase your risk.  

Vitamin B12 deficiency can cause a wide range of problems and may make you feel depressed or irritable and change the way you think, feel, and behave [8].  

If you think a vitamin deficiency may be the cause of any symptoms, speak to your GP. Our simple at-home blood tests can also give you an insight into what your vitamin levels are.   

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What’s the link between vitamin deficiencies and low mood?  

Nutrition and depression are profoundly linked, with studies showing that good nutrition can not only help your body function optimally but also delay long-term health and mental conditions such as dementia [9].  

What’s not so clear, is the exact mechanism by which how nutrition, gut health, and immune function influence mental health [9].  

Should I supplement? 

NICE (National Institute for Health and Care Excellence) recommends that to prevent vitamin D deficiency, a supplement should be taken through winter (or in some cases all year round). Vitamin B12 supplements are usually safe if taken at the right dose and you are monitoring your B12 levels closely. But as with any supplementation or medication, you should seek medical advice first.  

You can read more advice in our blog: what are vitamins, and should I supplement?  

The takeaway  

It’s normal for mood to fluctuate, but if you find you’re persistently feeling down or your mood is starting to affect other parts of your life, it’s best to talk to someone or arrange to see your GP.  

Sometimes (especially if you have other symptoms or risk factors) it may be appropriate to investigate other medical causes of low mood.   


  1.  BridgetChapple (no date) Depression and diabetesDiabetes UK. Diabetes UK. Available at: https://www.diabetes.org.uk/guide-to-diabetes/emotions/depression (Accessed: November 10, 2022).  
  2. Muijs, L.T. et al. (2020) “Glucose variability and mood in adults with diabetes: A systematic review,” Endocrinology, Diabetes & Metabolism, 4(1). Available at: https://doi.org/10.1002/edm2.152.  
  3. National Institute for Health and Care Excellence. Available at: https://www.nice.org.uk/guidance/ng145/chapter/Context 
  4. Psychological symptoms and thyroid disorders (no date) British Thyroid Foundation. Available at: https://www.btf-thyroid.org/psychological-symptoms-and-thyroid-disorders (Accessed: November 10, 2022).  
  5. Rivet-Noor, C. and Gaultier, A. (2020) “The role of gut mucins in the etiology of depression,” Frontiers in Behavioral Neuroscience, 14. Available at: https://doi.org/10.3389/fnbeh.2020.592388.  
  6. Zingone, F. et al. (2015) “Psychological morbidity of celiac disease: A review of the literature,” United European Gastroenterology Journal, 3(2), pp. 136–145. Available at: https://doi.org/10.1177/2050640614560786.  
  7. England, P.H. (2021) National Diet and Nutrition SurveyGOV.UK. GOV.UK. Available at: https://www.gov.uk/government/collections/national-diet-and-nutrition-survey (Accessed: November 10, 2022).  
  8. CKS is only available in the UK (no date) NICE. Available at: https://cks.nice.org.uk/topics/anaemia-b12-folate-deficiency/background-information/prevalence/ (Accessed: November 10, 2022).  
  9. Sathyanarayana Rao, T.S. et al. (2008) “Understanding nutrition, depression and mental illnesses,” Indian Journal of Psychiatry, 50(2), p. 77. Available at: https://doi.org/10.4103/0019-5545.42391.  

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