—Thiamin (B₁)  is necessary for normal growth, normal carbohydrate metabolism and   normal   functioning   of   the   heart, nerves, and muscles.  Thiamin deficiency results   in   retarded   growth   and   nerve disorders,   and   a   condition   known   as beriberi. Good sources include pork, fish, eggs, and whole-grain cereals. —Riboflavin (B₂) is required for normal growth, vigor, healthy skin and mucosa, and  normal  eye  function.    Riboflavin  is found   in   milk   products,   green   leafy vegetables, and eggs.  Other good sources of vitamin B₂  are the organ meats, heart, kidney, and liver. —Niacin  (B₃)   is  necessary  for  normal growth    and    skin    health,    normal functioning of the stomach and intestines, nervous and circulatory systems, and for carbohydrate, fat, and protein metabolism.   The best sources are meat, liver, poultry, and peanuts. —Pyridoxine  (B₆)  is  necessary  for  fat, carbohydrate,  and  protein  metabolism, and is sometimes used to treat nausea in pregnancy.   Sources include liver, yeast, wheat  germ,  pork,  potatoes,  and  milk. Vitamin   B₆   is  usually  prescribed  with Isonizid (INH) treatment since INH often causes a pyridoxine deficiency. —Cyanocobalamin  (B₁₂)   is   necessary for the health of nervous tissue and assists in  iron  metabolism  and  the  maturation process of red blood cells.   B₁₂ is used to prevent   pernicious   anemia. The   best sources are liver and kidneys, milk, eggs, fish, and cheese. See   Appendix   IV   for   more   information   on vitamins. VITAMIN AND MINERAL SUPPLEMENTS Vitamin supplements are usually not necessary if a diet includes a wide variety of foods.  Exceptions may occur in prenatal diets in which iron is low, as well as in patients   who   are   deficient   in   a   specific   vitamin. Vitamin   supplements   should   be   taken   only   on   a physician or dietitian’s recommendation. Vitamin and mineral supplements are being widely used  by  physically  active  people  because  of  all  the performance-enhancing  claims  made  by  supplement manufacturers.   It is estimated that 40–50 percent of a t h l e t e s   u s e   s o m e   f o r m   o f   v i t a m i n / m i n e r a l supplements.  Some doses range from amounts similar to the Recommended Dietary Allowances (RDA) up to levels many times the RDA.   Supplements are useful under a variety of conditions, such as if an individual ·   has an existing vitamin or mineral deficiency; ·   has poor nutrient intake and/or dietary habits; or ·   is exposed to extreme environmental conditions, such as altitude. Often,  laxatives  are  prescribed  in  conjunction  with some  medical  treatments  and  may  cause  decreased absorption of vitamins, loss of minerals and elec- trolytes, or inhibition  of  glucose  uptake.    Therefore,  any  patient  on laxatives should be carefully monitored, and supplementary nutritives should be administered as necessary. Taking a general multivitamin supplement appears to   be   without   measurable   performance   enhancing effects  in  healthy,  well-nourished,  physically  active personnel. Similarly,   no   improvements   in   muscle strength  or  endurance  have  been  noted  in  strength athletes,   such   as   body   builders,   who   tend   to   use megadoses of vitamin and mineral supplements.   The indiscriminate   use   of   high-potency   vitamins   and minerals   is   of   growing   concern   since   excessive amounts of vitamins and/or minerals can be harmful and   may   result   in   nutrient   imbalances. Excessive intake of some vitamin and mineral supplements can result in adverse—and possibly toxic–side effects. WATER Water   is   often   called   the   “forgotten   nutrient.” Water is needed to replace body fluids lost primarily in urine and sweat.   A person can survive weeks without food but only days without water.  Water makes up 70 percent of body weight and is found in every cell in the body.    It  is  the  medium  through  which  nutrients  are transported from the digestive tract to the cells where they  are  needed.    Water  is  also  the  medium  through which   the   by-products   of   cell   metabolism   are removed. Water  also  serves  as  the  medium  in  which  the chemical  processes  of  life  take  place.  It  is  normally taken into the body in beverages, soups, and in the form of   solid   foods. Fluid   needs   are   increased   with sweating, vomiting, diarrhea, high-protein diets, and in hot environments.  An insufficient intake may cause dehydration,  evidenced  by  loss  of  weight,  increased body temperature, and dizziness. 9-5