The reason for doing this research is that people with kidney disease often suffer from heart disease. Why this happens is not fully known. A possible cause may be high blood levels of a substance made by bacteria called "endotoxin". The blood levels of this substance are high in people with medium-level kidney disease.

We want to know if replacing normal amounts of Vitamin D can help lower the levels of this substance. We also want to know if replacing normal amounts of Vitamin D is associated with other changes that may help heart disease. We hope that our research will help figure out if levels of this substance can be lowered by replacing normal amounts of Vitamin D. Normal subjects are enrolled to have a 'control' set for comparison purposes.

Your participation in this study requires:

• 4 visits to the outpatient clinic (including 1 screening visit)
• Providing a blood sample (less than 5 tablespoons) and a urine sample at each visit
• Taking a test to measure how leaky your gut is. This test requires that you drink a small amount of liquid (about 4 ounces) and then collect your urine for 6 hours after drinking the liquid.

Inclusion Criteria:

Inclusion Criteria for Healthy volunteers

• Males and post-menopausal females, between the age of 50 -80.
• Vitamin D 25-OH level less than 20 ng/ml

Inclusion Criteria for Medium-level Kidney Function volunteers

• Males and post-menopausal females, between the age of 50 -80.
• Chronic kidney disease stage 3
• Vitamin D 25-OH level less than 20 ng/ml

Exclusion Criteria:

• Serum calcium level >10.5 mg/dl
• Serum phosphorus level > 5.5 mg/dl
• Serum PTH level < 35 pg/ml
• Active infection including HIV, Hepatitis B or C
• History of recent acute infection ( within 1 month)
• Gastrointestinal disease resulting in significant GI dysfunction or malabsorption
• Hgb< 10 g/dL
• Current use of Coumadin
• Current use of Vitamin D >400 IU/day
• Current use of systemic steroids or other immunosuppressants
• History of malignancy not in remission (>6 months)
• History of current ethanol abuse or illicit drug use
• History of significant emotional disorder within the past 5 years
• Participation in an investigational drug study within one month of screening
• Have any other condition, which in the opinion of the investigator, should prohibit the participation in the study