Vitamin D is thought to help support your mitochondria — the "powerhouses" in your cells that produce energy for your body to use. If you're deficient in vitamin D, you might feel exhausted and have a low mood.

Your body uses iron to make haemoglobin — a part of red blood cells that carries oxygen around your body. If you don't get enough iron you might develop iron deficiency anaemia. Tiredness, shortness of breath, and heart palpitations are signs you might be deficient.

Vitamin B12 and vitamin B9 (folate) are essential for good energy levels. This is because low levels can cause anaemia — where you can't properly transport oxygen around your body. This can cause extreme tiredness.

An HbA1c blood test measures your average blood glucose levels over the last 3 months. Normal to optimal HbA1c levels are linked to better energy levels.

Testosterone plays a role in red blood cell production — which is important for energy. Low testosterone levels are linked to anaemia, which can lead to tiredness and fatigue.