Analysis of Response of Subjects With Atopic Dermatitis or Psoriasis to Oral Vitamin D3

Inclusion Criteria (Main Study): * Definitive diagnosis of AD for at least 6 months, stringently diagnosed using the ADVN Standard Diagnostic Criteria, and has lesional skin present OR is a non-atopic healthy control subject with no personal or family history of food allergy, AD, asthma, or allergic rhinitis * Residing in the US. Inclusion Criteria (Sub-Study): * Definitive diagnosis of typical plaque psoriasis for at least 6 months, stringently diagnosed using the ADVN Standard Diagnostic Criteria; or is an AD or non-atopic healthy control subject participating in the main protocol ADVN CATH 03. * Residing in the US. Exclusion Criteria (Main Study): * Presence of atopy without stringent AD features, allowing only a presumptive diagnosis of AD * Presence of AD with exfoliative erythroderma * Presence of psoriasis * Pregnant or lactating females * Existence of ongoing dental disease (e.g., gingivitis) * History of bleeding disorders * Presence of severe AD that would be exacerbated by withholding of topical corticosteroids, oral or topical antibiotics, topical or systemic antihistamines, oral antivirals, immune enhancers (e.g., imiquimod), or topical calcineurin inhibitors within 7 days of Study Visit 2 (Baseline) and throughout the course of the trial * Receiving systemic immunosuppressives, chemotherapeutic agents, anti-inflammatory biologics (e.g., alefacept, etanercept), systemic, oral, injectable or inhaled steroids, vitamin D supplements (more than 400 IU daily) or oral calcineurin inhibitors 30 days prior to the Study Visit 2 (Baseline) or anytime during the course of the trial * Using topical corticosteroids, oral or topical antibiotics, oral antivirals, immune enhancers (e.g., imiquimod), topical or systemic antihistamines, or topical calcineurin inhibitors within 7 days of Study Visit 2 (Baseline) and during the course of the trial * Receiving phototherapy (e.g., UVB, psoralen plus ultraviolet light A \[PUVA\]) within 30 days of Study Visit 2 (Baseline) and during the course of the trial * Having autoimmune or immunodeficiency disease * Presence of active systemic fungal (excluding nail fungus), bacterial, or viral infections * History of or presence of active systemic malignancy, excluding uncomplicated non-melanoma skin cancer * Mental illness or history of drug or alcohol abuse that, in the opinion of the investigator, would interfere with the participant's ability to comply with study requirements * Inability or unwillingness of a participant to give written informed consent * Diabetes * Certain screening laboratory values not within normal limits, which would include calcium, serum PTH, and serum creatinine * History of kidney disease or kidney stones * Currently taking barbiturates such as phenobarbital (Luminal) * Currently taking carbamazine (Tegretol), digoxin, phenytoin (Dilantin) or fosphenytoin (cerebyx) * Currently taking diuretics such as thiazide diuretics, calcium channel blockers, or beta-blockers * Currently taking magnesium-containing antacids, mineral oil, cholestyramine (Questran), colestipol(Colestid), orlistat (xenical), the fat substitute Olestra, cod liver oil, fish oil, or omega 3 fatty acids * Currently taking oral antifungals such as ketoconazole * History of serious or life-threatening anaphylactic reaction to tape or adhesives * Lidocaine allergy * History of or active hyperparathyroidism, sarcoid, tuberculosis or lymphoma. Exclusion Criteria (Sub-Study): * Presence of AD with exfoliative erythroderma * Presence of psoriasis with exfoliative erythroderma or presence of guttate psoriasis, primary palmoplantar psoriasis, or pustular psoriasis * Pregnant or lactating females * Existence of ongoing dental disease (e.g., gingivitis) * History of bleeding disorders * Presence of psoriasis that would be severely exacerbated by withholding topical corticosteroids, oral or topical antibiotics, topical or systemic antihistamines, oral antivirals, immune enhancers (e.g.,imiquimod), or topical calcineurin inhibitors within 7 days of Study Visit 2 (Baseline) and throughout the course of the trial * Receiving systemic immunosuppressives, chemotherapeutic agents, anti-inflammatory biologics (e.g., alefacept, etanercept), systemic, oral, injectable, or inhaled steroids, vitamin D supplements (more than 400 IU daily), or oral calcineurin inhibitors, 30 days prior to the Study Visit 2 (Baseline) or anytime during the course of the trial * Using topical corticosteroids, oral or topical antibiotics, oral antivirals, immune enhancers (e.g., imiquimod), topical or systemic antihistamines, or topical calcineurin inhibitors within 7 days of Study Visit 2 (Baseline) and during the course of the trial * Receiving phototherapy (e.g., UVB, psoralen plus ultraviolet light A \[PUVA\]) within 30 days of Study Visit 2 (Baseline) and during the course of the trial * Having autoimmune or immunodeficiency disease * Presence of active systemic fungal (excluding nail fungus), bacterial, or viral infections * History of or presence of active systemic malignancy, excluding uncomplicated non-melanoma skin cancer * Mental illness or history of drug or alcohol abuse that, in the opinion of the investigator, would interfere with the participant's ability to comply with study requirements * Inability or unwillingness of a participant to give written informed consent * Diabetes * Screening laboratory values not within normal limits, which would include calcium, serum PTH, and serum creatinine * History of kidney disease or kidney stones * Currently taking barbiturates such as phenobarbital (Luminal) * Currently taking carbamazepine (Tegretol), digoxin, phenytoin (Dilantin) or fosphenytoin (cerebyx) * Currently taking diuretics such as thiazide diuretics, calcium channel blockers, or beta-blockers * Currently taking magnesium-containing antacids, mineral oil, cholestyramine (Questran), colestipol (Colestid), orlistat (xenical), the fat substitute Olestra, cod liver oil, fish oil, or omega 3 fatty acids * Currently taking oral antifungals such as ketoconazole * History of serious or life-threatening anaphylactic reaction to tape or adhesives * Lidocaine allergy * History of or active hyperparathyroidism, sarcoid, tuberculosis or lymphoma.