Vitamin D: can the sun stop the atopic epidemic?
Authors: Catherine M Hawrylowicz
Alexandra F Santos
Journal: Current Opinion in Allergy and Clinical Immunology (2020)
Discipline: IMMUNOLOGY
Keywords: Vitamin D; Atopic disease; Food allergy; Asthma; Allergic disease
Affiliations: Peter Gorer Department of Immunobiology, School of Immunology and Microbial Sciences, King's College London., Asthma UK Centre for Allergic Mechanisms in Asthma., Department of Women and Children's Health (Paediatric Allergy), School of Life Course Sciences, Faculty of Life Sciences and Medicine, King's College London., Children's Allergy Service, Guy's and St Thomas' Hospital, London, UK.

Abstract:  Purpose of review: To review recent evidence on the capacity of vitamin D to prevent atopic disease, focussing on food allergy and asthma, and potential underlying mechanisms. Recent findings: The incidence of allergic disease continues to increase worldwide. Vitamin D status is influenced by sun exposure and dietary intake. Vitamin D deficiency is linked to an increased incidence of allergic disease and asthma. These associations are generally strongest in early life. The capacity of vitamin D to enhance antimicrobial pathways, promote peripheral immunological tolerance and maintain mucosal barrier integrity may underlie these associations. Interventional studies have addressed the capacity of vitamin D supplementation in utero and early life to reduce the incidence of disease. Ancillary studies have provided insights into potential biological mechanisms linked to these effects. Summary: Observational studies show an inverse association between vitamin D levels and development of food allergy and asthma. Secondary analyses of two recent interventional studies suggest that achieving vitamin D sufficiency throughout pregnancy reduces the incidence of asthma/recurrent wheeze at 3 years. Longitudinal studies of vitamin D requirements in utero and postnatally, better understanding of factors that influence bioavailability of vitamin D and mechanistic insights into vitamin D effects on neonatal-specific immune pathways are awaited. 

Retracted: No

PubPeer comments:
 Pro-vitamin D biased review. Mixes serum level and supplement effects which should be kept apart. Ignores recent warnings about toxicity of vitamin D supplements in children (doi:10.1177 0004563219897691, doi: 10.1210 jc.2013-3655) Also ignores 30 studies that showed the opposite of their hypothesis eg an allergy promoting effect of vitamin D in animals (doi:10.1016 s0091-6749(03)01855-4), human cross-sectional (doi:10.1196 annals.1337.013) cohort studies (doi:10.1111 all.12081) as well as clinical trials (doi:10.1111 ped.12207). Rhetoric question in title that is not answered in the paper. Hasn t the sun been always shining ? , 
 #1 I also agree that the evidence regarding vitamin D appears to be quite mixed... As an interesting example, a recent paper on Mendelian randomization studies about vitamin D stated:  although we cannot rule out small beneficial effects of vitamin D supplementation for certain diseases, we can exclude large effects of vitamin D on the majority of studied outcomes, and that most of its attributed causal associations are likely driven by confoundingu201d . When considering the effects of sunlight, it might also be appropriate to consider also the other biological effects of the light exposure. According to numerous scientific reports describing a phenomenon called photobiomodulation , exposure to red and near-infrared light appears to have some biological effects that might also be anti-inflammatory . For example, skin exposure to red light seems to alleviate allergic symptoms in animals and irradiation with broadband light has shown some preliminary positive results in allergic rhinitis in humans . Since sunlight also contains red and near-infrared light, it might potentially also cause similar effects independently of vitamin D. This is just a speculation, though, but some other authors have also presented similar ideas (eg. https: journals.sagepub.com doi abs 10.1177 1477153519887520). , 
 #1  Rhetoric question in title that is not answered in the paper. Hasn t the sun been always shining ? [Betteridge s Law.] ,