Vitamin B3 and vitamin B6 are required to convert glutamic acid into glutamine. Biotin (vitamin B7) plays roles in fat and amino acid metabolism, and though there has been no conclusive evidence of its effect on the growth of hair and nails, it is commonly taken as a supplement for these purposes. Folate (vitamin B9) is required during synthesis of red blood cells, and during DNA replication. Folate cannot be synthesized de novo, and thus must be ingested from the diet. Vitamin C is a powerful antioxidant, and is a cofactor to many biological processes. Cobalmin (vitamin B12) is involved in cell metabolism, particularly in that of fatty acids and amino acids. The source of B12 is from the natural flora of the gut. Vitamin D enhances the absorption of minerals such as calcium, magnesium, and zinc from the gastrointestinal tract. Vitamin E is a fat-soluble antioxidant.

Alcoholism is associated with thiamine (vitamin B1) deficiency. This is due to multiple factors: poor nutrition, ethanol's inhibition of thiamin transport in the intestine, and reduced storage of thiamine in the liver due to fatty changes.

L-arginine is a precursor for the production of nitric oxide, essential to vasodilation. Other precursors to nitric oxide include NADPH, oxygen, and nitric oxide synthetase (NOS) enzymes. These other amino acids do not have essential roles in the nitric oxide synthesis pathway.

A physician is most likely to recommend decreased fluid intake in a patient that has renal disease, particularly if they are in any stage of renal failure. This is because a high fluid intake may put undue strain on the already impaired function of the kidney. Increased fluid intake is generally recommended for all of the other conditions listed.

The most common cause of copper deficiency in the United States is gastric bypass. This is due to malabsorption from food. Copper is fairly ubiquitous in soil and in the average American diet. Wilson's disease is a disorder of excess copper, rather than copper deficiency, resulting in a variety of neurological symptoms.   

Vitamin K deficiency can cause a variety of issues related to inability to form blood clots such as petechiae, excessive bleeding, bruising, heavy menses. This vitamin is also an important part of bone and cartilage formation, with deficiency resulting in malformation of developing bones and cartilage, or deposition of calcium into cartilage or arterial walls.

An intake of 1-6 grams of cinnamon has been shown in studies to lower blood sugar in patients with type 2 diabetes by as much as 25%, possibly due to its ability to improve insulin sensitivity.

The mot common cause of osteomalacia (known as rickets in children) in the United States is vitamin D deficiency. This is due to vitamin D's vital role in calcium absorption, homeostasis, and metabolism. Osteomalacia is categorized by the softening of the bones.

Vitamin C chelates non-heme iron in food while exposed to the acidic pH of the stomach. This chelated iron then becomes more soluble in the alkaline pH of the duodenum, resulting in increased intestinal absorption of iron.

Serotonin, melatonin, and niacin are all synthesized from L-tryptophan, an amino acid prevalent in many foods including chocolate, oats, dates, milk, sesame seeds, eggs, meat, and cheese. L-tyrosine is involved in the synthesis of dopamine. Acetylcholine is the neurotransmitter released at the neuromuscular junction, which stimulates contraction of skeletal muscle. Taurine has many biological functions in the cardiovascular, muscular, and nervous systems, as well as others.