Because they are soluble in water, excess B vitamins are generally readily excreted, although individual absorption, use and metabolism may vary…"  The elderly and athletes may need to supplement their intake of B 12 and other B vitamins due to problems in absorption and increased needs for energy production. [ medical citation needed ] In cases of severe deficiency, B vitamins, especially B 12 , may also be delivered by injection to reverse deficiencies.  [ unreliable medical source? ] Both type 1 and type 2 diabetics may also be advised to supplement thiamine based on high prevalence of low plasma thiamine concentration and increased thiamine clearance associated with diabetes.  Also, Vitamin B 9 (folic acid) deficiency in early embryo development has been linked to neural tube defects . Thus, women planning to become pregnant are usually encouraged to increase daily dietary folic acid intake and/or take a supplement. 
The list of vitamins and minerals below can give you an understanding of how particular vitamins and minerals work in your body, how much of each nutrient you need every day, and what types of food to eat to ensure that you are getting an adequate supply. The recommendations in this vitamins chart are based largely on guidelines from the Institute of Medicine. Recommended amounts may be expressed in milligrams (mg), micrograms (mcg), or international units (IU), depending on the nutrient. Unless specified, values represent those for adults ages 19 and older.