Introduction to Vitamins

Vitamins are vital to life and serve a variety of functions. They are typically needed in very small amounts in the diet to help regulate & support chemical reactions in the body. Generally, they cannot be synthesized in the body (exceptions: Vitamins D, K, Niacin, & Biotin). In order for it to be considered a vitamin, absence of the chemical must produce deficiency symptoms that are eliminated quickly once the substance is re-supplied.

In the 1930′s, nutrition was the most important medicine because it cured so many diseases. The 1st vitamin was discovered in 1915. They were named alphabetically. F & G were dropped… not sure why. The B complex was later sub-divided after more properties were discovered. A standard nomenclature for vitamins was established in 1979.

Vitamins are divided into 2 categories: Water soluble & Fat soluble
Water soluble: the B complex vitamins & Vitamin C. Daily intake is required as they are generally not stored in the body.
Fat soluble: Vitamins A, D, E, & K. Fat is required during ingestion in order for absorption.

RDA: Recommended Dietary Allowance. This level is set 20% above the maximum level that produces deficiency. In other words, if you can still have symptoms of deficiency at 10mg per day then the RDA would be set at 12mg per day. Keep in mind that this may NOT be the level for optimal health!

DRI: Dietary Reference Intake

Vitamin overview:

• fat soluble vitamins- (A, D, E, K) note that these are all deficient in fat malabsorption states (e.g., in cystic fibrosis there is pancreatic malabsorption of fat and fat soluble vitamins, in celiac disease, the loss of the villous surface leads to malabsorption of fats and fat soluble vitamins). They are probably absorbed through the lymphatics due to the fat absorption. They are stored in body tissues and, therefore, not required daily. They are more likely to be toxic. They are also less likely to be destroyed or decreased during cooking.
• water soluble- B₁: thiamine, B₂: riboflavin, B₃: niacin, B₅: pantothenic acid, B₆: pyridoxine, folate, B₁₂ (cobalamin) – all water soluble vitamins are co-factors for biochemical reactions
• reabsorption of vitamins- proximal small intestine, exception is Vitamin B₁₂ in the terminal ileum
• functions-
  • biochemical reactions: reducing agents: vitamin C, cofactors in oxidative decarboxylation (remove CO₂): thiamine, pyridoxine, oxidative phosphorylation: riboflavin (FAD, FMN), niacin (NAD⁺, NADP), carboxylase (add CO₂): blotin, transamination: pyridoxine, a components of coenzyme A: pantothenic acid, DNA synthesis: folate and B₁₂
  • cell growth/differentiation: vitamin A, folate and B₁₂
  • antioxidants: b-carotene, vitamin E, ascorbic acid
  • hormones: vitamin D
  • hemostasis: vitamin C, vitamin K
• toxicity- MC with fat soluble vitamins