<unk>  occurs when an organism lacks the required levels of<unk> , a critical nutrient in many species. Deficiency, although relatively rare in healthy well-nourished individuals, can have significant negative results, affecting the health of the heart and the nervous system; contributing to depression, anxiety, and dementia; and interfering with reproduction and gestation.
Selenium deficiency
Fluorine deficiency
Chromium deficiency
Boron deficiency 
Biotin deficiency
Copper deficiency
Thiamine deficiency
Zinc deficiency