Please select the eligibility criteria that correspond to the clinical trial below.
Title: Clinical Approaches to Correcting Vitamin D Inadequacy and Maintaining Adequacy
Brief Summary: Vitamin D is available in two forms, vitamin D2 and vitamin D3. It has previously been assumed that these two forms maintain blood vitamin D equally. However, this may not be the case. This study will evaluate whether D2 and D3 produce equal elevation of blood vitamin D. Additionally, it will evaluate whether once per month vitamin D dosing is as effective in maintaining blood vitamin D levels as daily dosing.


Options:
A: Inclusion Criteria:

* willingness to withhold supplement use for duration of study
* willingness to avoid sun exposure for duration of study

Exclusion Criteria:

* vitamin D supplement use
* conditions that affect vitamin D metabolism by the body
B: Inclusion Criteria:

* Men or women, between 18 and 65 years of age, who are capable of providing informed consent.
* BMI of 25 to 35 kg/m2.
* Non-smoker (for at least 6 months).
* In good health, as determined by the principal investigator based on medical history and physical examination.
* Clinical laboratory evaluations (including Biochemistry, Hematology, Endocrinology) within the reference range for the test laboratory, unless deemed not clinically significant by the Investigator.
* Because of the calorie-restricted diet and radiation exposure from the CT scan, females will be non-pregnant, non-lactating, and either post-menopausal for at least 1 year, surgically sterile for at least 3 months, or be willing to use an approved method of contraception (which may include use of abstinence; intrauterine device; female condom with spermicide; diaphragm with spermicide; cervical cap with spermicide; oral or transdermal hormonal contraceptives; a condom with spermicide by the sexual partner; or a sterile sexual partner) from 35 days prior to study entry (i.e., Day -1) until 30 days following Study Completion. For all females, the pregnancy test result must be negative at the screening visit and at visits when a CT scan will be done.
* Ability to comprehend and willingness to sign the Informed Consent Form for this study.
* Ability to comply with study restrictions regarding diet and exercise.
* Stable weight (+ 5%) for at least 3 months prior to study entry.

Exclusion Criteria:

* Diabetes mellitus.
* History or clinical manifestations of significant metabolic, hepatic, renal, hematological, pulmonary, cardiovascular, gastrointestinal, urological, neurological, or psychiatric disorders which in the opinion of the investigator would be expected to interfere with the study or increase risk to the subject.
* Participation in any other investigational diet study within 90 days prior to study entry.
* History of a medical or psychological condition or social circumstances that would impair the subject's ability to participate reliably in the study.
* Use within the last six months of medications that can result in significant weight gain or weight loss, including antipsychotics, selective serotonin reuptake inhibitors, anti-epileptic drugs, appetite-suppressants such as phentermine and sibutramine, and the lipase-inhibitor orlistat. (see Appendix 1 for detailed list)
* Active eating disorder.
* History of alcoholism or substance abuse within 5 years prior to study entry.
* Recommendation by a physician to avoid calcium supplements because of a history of kidney stones or other medical condition.
* History of hyperparathyroidism or sarcoidosis.
* Osteoporosis or other medical condition for which a physician has recommended taking a multivitamin or calcium supplementation.
* High calcium intake (more than 2 servings of dairy products per day or taking calcium supplements \> 3x/wk ) for 1 month prior to study start date and for duration of study. (If participant is taking calcium supplement \> 3x/wk or more than 2 servings of dairy products per day, they are eligible to participate if they agree to stop for 1 month prior to study start date and for the duration of the study. Participants will similarly be asked to stop multivitamins as the majority of these supplements contain calcium.)
* General medical conditions that are well-controlled will not be a basis for exclusion in the study. Subjects with uncontrolled conditions that are not adequately controlled or that might pose an unacceptable risk for participation, as clinically determined by the investigators, will be excluded.
C: Inclusion Criteria:

* Clinically definite MS
* Age 18-55
* EDSS 0-6.5

Exclusion Criteria:

* EDSS =\> 7.0
* Current Vitamin D3 use \>4000 IU/d
* Baseline (25(OH)D) level \<20 mmol/L (frank deficiency) and \>150 mmol/L
* Pregnancy or inability/unwillingness to use contraception
* History of cardiac arrhythmia
* History of renal disease and nephrolithiasis
* History of granulomatous disease or lymphoma
* Relapse activity or steroid use in the past 60 days
D: Inclusion Criteria:

1. Community dwelling men and women age ≥ 65 years.
2. Able and willing to sign informed consent.
3. Serum 25OHD concentration ≥ 10 and less than 60 ng/ml by HPLC.
4. Willing to avoid use of cod-liver oil and non-study vitamin D supplementation; standard multiple vitamins containing ≤ 400 IU used no more than once daily will be allowed

Exclusion Criteria:

1. Current hypercalcemia (serum calcium \> 10.5 mg/dl) or untreated primary hyperparathyroidism.
2. History of nephrolithiasis.
3. Screening 25OHD concentration ≥ 60 ng/ml.
4. Baseline 24-hour urine calcium \> 250 mg if female, \> 300 mg if male.
5. Known risk factors for hypercalcemia, e.g., malignancy, tuberculosis, sarcoidosis, Paget's disease
6. History of any form of cancer within the past five years with the exception of adequately treated squamous cell or basal cell skin cancer.
7. Renal failure defined as a calculated creatinine clearance (Cockroft-Gault method) ≤ 25 ml/minute
8. Severe end-organ disease, e.g., cardiovascular, hepatic, hematologic, pulmonary, etc., which may limit ability to complete the study
9. Known malabsorption syndromes, e.g., celiac disease, radiation enteritis, active inflammatory bowel disease, etc.
10. Use of medications known to alter bone turnover including bisphosphonates, estrogen, selective estrogen receptor modulators, PTH, testosterone or calcitonin
11. Vitamin D intake greater than 5,000 IU daily
12. Treatment with any active metabolites of vitamin D within six months of screening
13. Treatment with any drug which may interfere with vitamin D metabolism, e.g., phenobarbital, phenytoin.

Answer: D