This is an extract of the work of Scott Byrnes with my recommendation at the end in red italics.

“There is now convincing evidence that exposure to the ultraviolet (UV) component of sunlight protects us from developing a number of autoimmune diseases including type 1 diabetes, Juvenile onset Crohn’s, Crohn’s disease & colitis, Sjögren’s syndrome & possibly rheumatoid arthritis. CNS-autoimmune diseases such as multiple sclerosis (MS) show the most striking inverse correlation with UV (1). In Australia, MS incidence increases with distance away from the equator with Tasmanians being almost 7 times more likely to develop MS than Queenslanders (2). Recent Australian studies have confirmed that higher UV amounts reduce the incidence of a patients 1st clinical diagnosis of CNS demyelination (3), many of whom will develop clinically confirmed MS. This is important because it shows that UV is able to prevent both the development and progression of MS. However, despite intense community interest in understanding how increasing the amount of UV we receive leads to a reduction in autoimmune diseases, the mechanisms by which UV provides this protection remains unknown.”

Sunlight has 2 major known effects on internal organs:

(1) UV produces Vitamin D3: However, UV-induced Vitamin D3 was very recently shown to not be responsible for UV protection from a mouse model of MS (4). Even more recently it was shown that Vitamin D3 and UV have independent roles in protection from MS development (5)

(2) UV is potently immunosuppressive (6). We (Scott Byrnes et al) have discovered that one way UV suppresses immunity is via the activation of an IL-10 producing regulatory B cell (UV-B-regs) (7-10). Because regulatory B cells are known to mediate protection from a range of autoimmune diseases it is the hypothesis of this project that UV-induced activation of regulatory B cells is the mechanism by which UV protects from autoimmunity.”

Macquarie Stem Cells recommend patients to then not take vitamin D supplements and rather use their vitamin D levels as a reference for whether they are getting enough sunlight. Exposing face, hands and arms for 5-15 minutes of sun, 4-6 times per week can prevent vitamin D deficiency. It is important to choose a time outside of 10am-2pm (11am-3pm daylight saving) as skin damage is more likely. (11)

References:

(1) van der Mei, et al. Past exposure to sun, skin phenotype, and risk of multiple sclerosis: case- control study. BMJ 327, 316 (2003).
(2) McLeod, et al. Epidemiology of multiple sclerosis in Australia. With NSW and SA survey results. Med J Aust 160, 117-122 (1994).
(3) Taylor, et al. Latitudinal variation in incidence and type of first central nervous system demyelinating events. Mult Scler 16, 398-405 (2010).
(4) Becklund, et al. UV radiation suppresses experimental autoimmune encephalomyelitis independent of vitamin D production. Proc Natl Acad Sci U S A 107, (2010).
(5) Lucas et al. Sun exposure and vitamin D are independent risk factors for CNS demyelination. Neurology 76:6, 540-8 (2011)
(6) Byrne et al. Ultraviolet-A Irradiation of C57BL/6 Mice Suppresses Systemic Contact Hypersensitivity or Enhances Secondary Immunity Depending on Dose. J Invest Dermatol 119:4, 858-864 (2002)
(7) Byrne and Halliday. B Cells Activated in Lymph Nodes in Response to Ultraviolet Irradiation or by Interleukin-10 Inhibit Dendritic Cell Induction of Immunity. J Invest Dermatol 124:3, 570-578 (2005)
(8) Byrne et al. Ultraviolet B but not A radiation activates suppressor B cells in draining lymph nodes. Photochemistry and Photobiology 81:6, 1366-70 (2005)
(9) Matsumura and Byrne et al. A role for inflammatory mediators in the induction of immunoregulatory B cells. J Immunol 177:7, 4810-4817 (2006)
(10) Byrne et al. Mast cell migration from the skin to the draining lymph nodes upon UV-irradiation represents a key step in the induction of immune suppression. J Immunol 180:7, 4648-4655 (2008)
(11) Article attached