The Effect of Vitamin C on Growth Hormone Secretion

Obesity is associated with reduced growth hormone (GH) secretion. GH secretion is regulated by nutritional stimuli including fasting, insulin, glucose and free fatty acids. However, the role of micronutrients, such as vitamins, on GH secretion has not been investigated in much detail. Vitamin C levels are also reduced in obesity, and the investigators recently demonstrated a possible role for dietary vitamin C intake in the regulation of GH secretion in two preliminary retrospective studies. The investigators therefore propose a more detailed prospective physiological study to examine the effects of increasing dietary vitamin C intake on GH secretion in a physiologic, intervention study. The investigators hypothesize that increasing vitamin C concentrations in obese subjects with sub-optimal plasma vitamin C levels and reduced GH secretion will increase GH secretion.

• Obese
• Disorder of Vitamin C
• Growth Hormone Secretion Abnormality

• Dietary Supplement: Placebo
• Dietary Supplement: Vitamin C 250 mg once daily
• Dietary Supplement: Vitamin C 1,000 mg once daily

• Active Comparator: Vitamin C low dose
  vitamin C 250 mg oral once daily
  Intervention: Dietary Supplement: Vitamin C 250 mg once daily
• Active Comparator: Vitamin C high dose
  vitamin C 1,000 mg oral once daily
  Intervention: Dietary Supplement: Vitamin C 1,000 mg once daily
• Placebo Comparator: Placebo
  Placebo oral once daily
  Intervention: Dietary Supplement: Placebo

Inclusion Criteria:

1. Men and women age 18-60
2. BMI ≥ 30 kg/m2
3. Waist circumference ≥ 102 cm in men and ≥ 88 cm in women
4. Plasma vitamin C concentration ≤ 23 µmol/l
5. Peak stimulated GH ≤ 4.2 µg/l upon GHRH-arginine stimulation test

Exclusion Criteria:

1. History of hypopituitarism, pituitary surgery, pituitary/brain radiation, recent traumatic brain injury or any other condition known to affect the GH axis.
2. History of severe chronic illness including anemia, chronic kidney disease, liver disease, oxygen dependent COPD or HIV
3. Subjects on testosterone, glucocorticoids, anabolic steroids, GHRH, GH or IGF-1 within 3 months of enrollment
4. Use of dietary supplements including vitamin C or once daily multi-vitamins
5. Subjects with Hgb < 912 g/dL, SGOT > 2.5x upper limit of normal or Creatinine > 1.5 mg/dL
6. Subjects with poorly controlled diabetes, defined as HbA1c > 8%.
7. Changes in lipid lowering or anti-hypertensive regimen within 3months of screening
8. Subject is currently enrolled in another investigational device or drug trial(s), or subject has received other investigational agent(s) within 28 days of baseline visit
9. Any condition judged by the patient's physician to cause this clinical trial to be detrimental to the patient.