• INCLUSION CRITERIA: (Overweight Subjects)

Volunteers will qualify if they meet the following criteria:

1. Good general health. Individuals taking medication for obesity-related co-morbid conditions will not be excluded.
2. Age greater than or equal to 18 years.
3. Body Mass Index greater than or equal to 25 kg/m(2).
4. For women with childbearing potential, a negative pregnancy test at the initial evaluation.
5. Normal fasting serum Ca (2.05-2.55 mmol/L) and serum phosphorous levels (2.3 - 4.3 mg/dl).

INCLUSION CRITERIA: (Normal Weight Subjects)

Volunteers will qualify if the meet the following criteria

1. Good general health.
2. Age greater than or equal to 18 years.
3. Body Mass Index 1-24.99 kg/m(2)
4. For women with childbearing potential, a negative pregnancy test at the initial evaluation. Since these subjects have to undergo DXA (dual Energy X-ray Absorptiometry) scan screening in their second visit, for safety purposes, pregnant women will be excluded from participation in the study.

5. Normal fasting serum Ca (2.05-2.55 mmol/L) and serum phosphorus levels (2.3-4.3 mg/dl).

   EXCLUSION CRITERIA: (overweight subjects)

   Volunteers will be excluded (and referred to non-experimental treatment programs as needed) for the following reasons:

   1. A presence of major illnesses: renal, hepatic (other than obesity-related steatosis), gastrointestinal, most endocrinologic (e.g., Cushing syndrome, hyper- or hypothyroidism), hematological problems or pulmonary disorders (other than asthma not requiring continuous medication or sleep-apnea related disorders);
   2. Women who are pregnant, or who are currently nursing an infant; or who are having unprotected intercourse;
   3. Individuals who have a current substance abuse or a psychiatric disorder or other condition that in the opinion of the investigators would impede competence or compliance or possibly hinder completion of the study;
   4. Subjects who regularly use prescription medications unrelated to the complications of obesity {e.g., calcium channel blockers, diuretics (including thiazide diuretics), beta-blockers etc}. Oral contraceptive use will be permitted, provided the contraceptive has been used for at least two months before starting study medication. The use of over-the-counter medications will be reviewed on a case-by -case basis;
   5. Subjects who have a total calcium intake of more than 3.5 g/day on the screening calcium intake questionnaire (SCQ) or more than 3 g/day of total calcium intake on review of their 7-day food diaries;
   6. Subjects who take supplement calcium in excess of 300 mg/day or vitamin D supplements in excess of 400 IU/day;
   7. Recent (3 months) use of anorexiant medications;
   8. History of renal stones;
   9. Intentional weight change of more than 3% of body weight in the past two months.
   10. Post-menopausal women who are medically advised to take calcium supplementation.
   11. Subjects with iPTH greater than 75 pg/ml (Normal range: 10-75 pg/ml) when associated with a serum calcium level greater than 2.5 mmol/L. (normal range 2.05 to 2.55 mmol/L)
   12. Subjects with a serum 25-(OH)-D level less than 10 ng/ml (Normal range: 10-68 ng/ml) when associated with a serum 1-225-(OH)(2)-D level of less than 22 pg/ml (Normal Range: 22-67 pg/ml.
   13. Subjects with a consistently (2 weeks apart) elevated systolic blood pressure of greater than 160 mm Hg and/or a diastolic blood pressure greater than 95 mm Hg.

   EXCLUSION CRITERIA: (Normal Weight Subjects)

   Volunteers will be excluded (and referred to non-experimental treatment programs as needed) for the following reasons:

   1. Presence of major illnesses: renal (serum creatinine greater than 1.6), hepatic (AST/ALT greater than 3 times upper limit of normal range used in Clinical Center assays), gastrointestinal, most endocrinologic (e.g. Cushing syndrome, hyper- or hyothyroidism), hematological problems or pulmonary disorders (other than asthma not requiring continuous medication or sleep-apnea related disorders);
   2. Women who are pregnant, or who are currently nursing an infant;
   3. Individuals who have current substance abuse of a psychiatric disorder or other condition that in the opinion of the investigators would impede competence or compliance or possibly hinder completion of the study;
   4. Subjects who regularly use prescription medications. Oral contraceptive use will be permitted, provided the contraceptive has been used for at least two months before starting study medication. Individuals taking medications for most conditions will be excluded, but medication use will be considered on a case-by-case basis.
   5. Subjects who take supplemental calcium in excess of 300 mg/day or vitamin D supplements in excess of 400 IU/day.
   6. Recent (3 months) use of anorexiant medications;
   7. Intentional weight change of more than 3% of body weight