PRAgmatic Trial in Atopic Dermatitis Testing Long-term Control Effectiveness of New Phototherapy Regimen During Winter Coupled With Oral Vitamin D Supplementation vs. Placebo

Inclusion Criteria: * Patients with atopic dermatitis (Hanifin and Rajka criteria), * Aged 15 years or more, * With \> 2 years of disease evolution, * With moderate-to-severe disease (IGA \> 2), * Patients that have received TAT for at least 12 weeks and have symptoms requiring an increase in therapy, * Seasonality in disease severity (based on a questionnaire assessing disease improvement during summer), * Easy access to a phototherapy cabin (widely implanted in primary care dermatology private practice in France), * Effective contraception to be used at least 30 days before initiation of treatment, during treatment and 29 weeks after last administration for women of reproductive age, * Written informed consent of the patient * For patients aged between 15 and 18, written informed consent of the parents and of the teenager. Exclusion Criteria: * Any cause of contra-indication for vitamin D supplementation: flare of granulomatosis, primary hyperparathyroidism, * Clinical suspicion of hypercalciuria, * Indication to a systemic immunosuppressant in the next 2 years, * Atopic dermatitis known to be aggravated by UV exposure, * Any contra-indication for artificial or solar exposure including: genetic diseases with a predisposition to skin cancer, any history of personal skin cancer (melanoma, squamous cell skin cancer, basal cell skin cancer), lupus, dermatomyositis, any other photosensitizing skin disease, photosensitizing medication (see appendix 2), * More than 100 previous phototherapy sessions in lifetime, * Pregnancy or breastfeeding, * Persons subject to major legal protection (safeguarding justice, guardianship, trusteeship), persons deprived of liberty.