If you're deficient in anything you will suffer mental and physical effects. Quite often correcting an imbalance will make a huge difference. Even some serious pathological conditions have been reversed by giving the cells what they need. Common deficiencies include vitamin D! Especially if you live in cold climates and spend a lot of time indoors, vitamin K, magnesium (these three are very potent together) iodine and selenium deficiencies are also very common, they too are symbiotic.