Often when we are low on energy it can be a sign of a deficiency in iron, vitamin B12, magnesium, vitamin D, and potassium. These can easily be checked by doing a simple blood test. 
 
Iron is usually the most common deficiency (and more common in woman than men) causing us to feel fatigue. Iron boosts the formation of haemoglobin which is the primary transporter of oxygen from our lungs to our body tissue. 
 
Deficiency in vitamin B12 is another one of the most common deficiencies - making sure you are getting enough in your diet is important for maintaining energy levels as it’s needed to convert the carbohydrates we eat into glucose which provides our body with energy. It additionally helps with the formation of red blood cells!
 
Magnesium deficiency can leave us feeling fatigued, weak and cause muscle cramps. We need it to support muscle and nerve function in addition to energy production.
 
Vitamin D deficiency like magnesium can cause fatigue along with muscle weakness and depression.
 
Low levels of potassium can result in muscle fatigue and lack of energy. Potassium is important in helping with muscle contractions.