With the COVID19 pandemic, the entire world has been brought to a halt. Whole populations are confined at home and some people barely go outside. Even if social distancing is probably the best way to “flatten the curve”, lack of time outdoor might have an unpredicted downside. SARS-CoV2 uses the Angiotensin-converting enzyme 2 (ACE2) as receptor to infect cells and downregulate ACE2 expression at the cell surface. ACE2 has a protective effect against damage due to inflammatory processes. In severe and critical illness, this leads to unopposed inflammation, cytokine storm and acute respiratory distress syndrome (ARDS). To defend against this infection, we need a well-balanced immune responses. The immune system must be activated to get rid of the virus and protect against opportunistic infections, but must be contained to prevent a downward spiral toward ARDS. Vitamin D is known to activate many effectors of the immune system useful against viruses, but, also, cells responsible of modulating its response and opposing the pro-inflammatory mediators. It can also upregulate ACE2 cell expression by binding to the vitamin D receptor (VDR) that will bind to the ACE2’s gene regulatory sequence and promote its transcription. Unfortunately, vitamin D deficiencies are common and levels are at their lowest in the northern hemisphere at this time of year. This is why a high dose prophylactic supplementation of vitamin D should be given vulnerable populations; nursing home resident, and elderlies in general, health care workers, first responders, essential service workers and African-Americans.