B vitamins are active in the body and form coenzymes that assist enzymes in releasing energy.
Recommendations are expressed as RDIs, AIs, and upper levels of intake.
RDI: Recommended Dietary Intake.
AI: Adequate Intake (set when RDI information is insufficient).
Each B vitamin has unique deficiencies, toxicities, and food sources that are likely to be assessed.
Thiamine (Vitamin B1)
Absorption:
Absorbed in the duodenum and jejunum of the small intestine via active transport using a carrier.
Alcohol inhibits absorption, leading to deficiency in alcoholics. This is often compounded by poor dietary intake.
Utilization:
Tissues take up thiamine and phosphorylate it into thiamine pyrophosphate (TPP).
Excess is excreted in urine and may be lost in sweat.
Limited storage in the body; deficiency can occur within days.
Importance:
Needed for aerobic metabolism.
TPP is involved in the conversion of pyruvate to acetyl CoA in the TCA cycle.
Without thiamine, pyruvate builds up in the mitochondria, and lactate builds up in the cytosol.
Deficiency Symptoms:
Enlarged heart or cardiac failure.
Muscular weakness.
Apathy, short-term memory loss, confusion, and irritability.
Anorexia and weight loss.
Beriberi:
Wet Beriberi: Presents with edema. High carbohydrate intake with TPP deficiency causes excess pyruvate buildup, leading to fluid movement into interstitial tissues.
Dry Beriberi: Presents with muscle wasting. Associated with low energy and low carbohydrate intake.
Wernicke-Korsakoff Syndrome:
Severe deficiency in chronic alcohol consumption.
Can lead to brain damage, confusion, and hallucinations.
Requirements:
RDI for men: 1.2 mg/day.
RDI for women: 1.1 mg/day.
No toxicities reported.
Food Sources:
Whole grains, breakfast cereals, and meats.
Other Considerations:
Easily destroyed by heat; bread makers add it during fortification to compensate for losses.
Leaches into water during boiling or blanching.
Riboflavin (Vitamin B2)
Absorption:
Absorbed in the upper small intestine.
Milk and eggs contain free riboflavin; most in foods is present as flavin coenzymes.
Flavin Coenzymes:
Flavin adenosine dinucleotide (FAD) is produced in the TCA cycle.
Storage and Excretion:
No significant storage; surplus is rapidly excreted in urine, causing fluorescence.
Function:
Part of the FADH complex and attached to diphosphate, ribose, and adenine.