# Vitamin B3 (Niacin) Biochemistry

**Summary**  
Vitamin B3 (Niacin) is a water-soluble vitamin which serves a key role as a precursor of the coenzymes NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate). Found in foods, niacin is also used pharmacologically as a treatment for [lipid disorders](/content/browse#playlist-1954/index.html), specifically for its ability to raise HDL ("good" cholesterol) and lower VLDL and LDL ("bad" cholesterols). The synthesis of niacin requires a number of factors, including tryptophan, [Vitamin B2 (Riboflavin)](/content/view/3681/index.html), and [Vitamin B6 (Pyridoxine)](/content/view/3763/index.html).

**Key Points**  
- **Vitamin B3 (Niacin)**  
  - Constituent of **NAD+** and **NADP+** (used in redox reactions)  
  - Synthesis requires **tryptophan**, [**Vitamin B2**](/content/view/3681/index.html) and [**Vitamin B6**](/content/view/3763/index.html)  
    - Depletion of tryptophan can cause [**Niacin Deficiency**](/content/view/3716/index.html)  
      - [**Carcinoid Syndrome**](/content/view/2784/index.html) (depleted for serotonin synthesis)  
      - [**Hartnup Disease**](/content/view/3903/index.html) (lost in feces and urine)  
  - Used to **treat dyslipidemia**  
    - **Raises HDL levels**  
    - Lowers VLDL, triglyceride, LDL levels  
      - Decreases hepatic production of VLDL, triglyceride release from adipose tissue, and decreases conversion VLDL to LDL

Find Niacin Biochemistry and other [Vitamins](/content/browse#playlist-2700/index.html) among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.