21/10/2025
Experiencing fatigue and or depression and want to know what to look for?
It's not always in your head.
Some mental health issues (including depression, fatigue, low motivation and anxiety) can be caused by imbalances within our physical health - and blood tests can be useful in diagnosing some of these issues.
It’s important to have your blood tests reviewed by a health professional who will look beyond blood tests simply being ‘within range’. Being within range, may not be optimal for your mental well-being.
This is by not means an exhaustive list - but some good basic things to start with. You can find more information on blood tests for mental health here
Vitamin B12
There is some evidence of a relationship between low B12 and depression or anxiety. B12 is involved in general energy production, DNA syntheses - low B12 is associated with fatigue. Anemia can be brought on by a B12 deficiency. Anemia can effect energy levels, sleep, mood etc
Vitamin B12 supplementation with antidepressants significantly improved depressive symptoms in one study.
IDEAL LEVELS >350
Ferritin
Low iron can be associated with poor sleep, low energy and low mood. Iron is necessary for neurotransmitter production and the production of red blood cells.
High ferritin levels (over 200) - are associated with increased inflammation in the body (and other illnesses)
IDEAL LEVELS 30 - 100
Zinc
Serum blood testing of zinc isn’t necessarily that accurate - as the body is very good at ensuring homeostasis of blood levels and there are fluctuations of zinc levels throughout the day. However, a very low level (less than 7) may be indicative of low zinc overall.
Zinc is essential for neurotransmitter function. It is also important for the immune system, red blood cell production, hormone production and gastric acid production - lack of which can contribute to nutrient deficiencies. Not necessarily accurate in serum blood tests.
IDEAL LEVEL > 13
CRP C Reactive Protein
This is a common marker and an indicator of inflammation. Inflammation is associated with depression. CRP levels have been found to be significantly higher in patients with depression relative to control subjects
IDEAL LEVEL < 1
Cortisol
Cortisol is often thought of as the ‘stress hormone’ and although it’s released in times of stress - it’s also necessary to provide us with energy and ‘get up and go’ - especially in the morning when they are highest. They should then decline throughout the day and be lowest at night - so you can sleep.
You don’t want levels too high or too low. Cortisol levels ideally should be done first thing in the morning.
Blood sugar dysregulation is associated with abnormal cortisol levels (and visa-versa).
Folate
Folate is necessary for neurotransmitter production. Approximately only half of New Zealanders meet the recommended dietary intake of folate for adults.
Folate deficiency is also relatively common in depressed people, with approximately one-third of depressed individuals having an outright deficiency. Depressed individuals with low serum folate also tend to not respond well to selective serotonin reuptake inhibitor (SSRI) antidepressant drugs.
IDEAL LEVELS: >17
TSH (Thyroid-stimulating Hormone)
TSH is - is produced by the pituitary gland in response to circulating thyroid hormones in the blood.
The thyroid produces various hormones which help to regulate general metabolism.
Abnormalities in thyroid production can cause depression, anxiety, weight, sleep, skin and many other problems.
If TSH is abnormal, I would recommend investigating T4, T3 & TPO & TG antibodies.
IDEAL LEVELS 0.5 - 2.5
Vitamin D
Needs to be self-requested. Studies have identified that up to 90% of those admitted to a psychiatric unit are low in vitamin D. (In NZ - in one study 75%). Low vitamin D levels have been associated with several diseases including arthritis, autoimmune disease and depression. For vitamin D to be absorbed - you require vitamin K2 and magnesium.
IDEAL LEVEL >75nmol/L
Magnesium
Serum magnesium is also not an accurate test to measure actual magnesium levels in the body - however, very low levels once again may be indicative of low magnesium. Low levels of magnesium can be correlated with depression and anxiety. Magnesium is an essential mineral for many processes in our body - including neurotransmitter production.
HbA1c
HbA1c is a marker of your blood glucose levels over a period to 10 - 12 weeks. Studies have shown that anxiety and depressive disorders in diabetic patients may be twice as high as in the general population. High levels of HbA1c (41 – 49 mmol/mol) indicate pre-diabetes and an HbA1c over ≥ 50 mmol/L indicates diabetes. Other tests can be done - for example fasting insulin - to get a clearer picture.
Check your HbA1c levels over time - they should be steady and not continuously increasing.
IDEAL LEVELS
What blood test are important in mental health? Some mental health issues (including depression, fatigue, low motivation and anxiety) can be caused by imbalances within our physical health - and blood tests can be useful in diagnosing some of these issues. Nurse & life coach from One Live takes