Exposure to solar ultraviolet radiation and respiratory tract symptoms in 1-year-old children

Vitamin D as an adjunctive therapy in asthma. Part 2: A review of human studies

Vitamin D deficiency (VDD) is highly prevalent worldwide, with adverse effects on bone health but also potentially other unfavorable consequences. VDD and asthma-incidence/severity share many common risk factors, including winter season, industrialization, poor diet, obesity, dark skin pigmentation, and high latitude. Multiple anatomical areas relevant to asthma contain both the enzyme responsible for producing activated vitamin D and the vitamin D receptor suggesting that activated vitamin D (1,25-dihydroxyvitamin D) may have important local effects at these sites. Emerging evidence suggests that VDD is associated with increased airway hyperresponsiveness, decreased pulmonary function, worse asthma control, and possibly decreased response to standard anti-asthma therapy. However the effect is inconsistent with preliminary evidence from different studies suggesting vitamin D is both beneficial and detrimental to asthma genesis and severity. Current evidence suggests that supplementation with moderate doses of vitamin D may be appropriate for maintenance of bone health in asthmatics, particularly steroid users. However emerging data from an increasing number of randomized, controlled, intervention studies of vitamin D supplementation in pediatric and adult asthma are becoming available and should help determine the importance, if any of vitamin D for asthma pathogenesis. The purpose of this second of a two-part review is to review the current human literature on vitamin D and asthma, discussing the possible consequences of VDD for asthma and the potential for vitamin D repletion as adjunct therapy.

Vitamin D as an adjunctive therapy in asthma. Part 1: A review of potential mechanisms

Vitamin D deficiency (VDD) is highly prevalent worldwide. The classical role for vitamin D is to regulate calcium absorption form the gastrointestinal tract and influence bone health. Recently vitamin D receptors and vitamin D metabolic enzymes have been discovered in numerous sites systemically supporting diverse extra-skeletal roles of vitamin D, for example in asthmatic disease. Further, VDD and asthma share several common risk factors including high latitude, winter season, industrialization, poor diet, obesity, and dark skin pigmentation. Vitamin D has been demonstrated to possess potent immunomodulatory effects, including effects on T cells and B cells as well as increasing production of antimicrobial peptides (e.g. cathelicidin). This immunomodulation may lead to asthma specific clinical benefits in terms of decreased bacterial/viral infections, altered airway smooth muscle-remodeling and -function as well as modulation of response to standard anti-asthma therapy (e.g. glucocorticoids and immunotherapy). Thus, vitamin D and its deficiency have a number of biological effects that are potentially important in altering the course of disease pathogenesis and severity in asthma. The purpose of this first of a two-part review is to review potential mechanisms whereby altering vitamin D status may influence asthmatic disease.

The effects of a mid-winter 8-week course of sub-sunburn sunbed exposures on tanning, vitamin D status and colds

Like UV irradiation, which generates vitamin D(3) in the skin, the hormonally active metabolite, 1,25-dihydroxyvitamin D(3), boosts innate immunity against viruses and bacteria. Epidemiologic studies have found high vitamin D levels to be associated with lower risk of infections of the upper respiratory tract (colds). We have therefore performed an intervention study in 105 young adults (ages 18-30 years; 91% female) over a mid-winter 8-week period (January-March 2010). The participants were randomised to 3 groups: (A) subjected to 3 times a week sub-sunburn sunbed exposure (n = 35), (B) daily vitamin D supplementation, @ 1000 IU (n = 37), and (C) a control group without any intervention (n = 33). The mean serum level of 25-hydroxyvitamin D (25(OH)D) dropped from 62 to 55 nmol l(-1) in group C, while these levels rose from 62 to 109 and from 58 to 93 nmol l(-1) in groups A and B, respectively (p < 0.001). The skin on the chest darkened significantly in group A (mean difference in lightness, L*, equalled -5.7, p < 0.001), correlating significantly, but weakly, with increases in 25(OH)D (3.3 nmol l(-1) per unit drop in L*, R(2) = 0.17, p = 0.014). The percentage of self-reported colds with proper signs and symptoms was only slightly and not significantly reduced in groups A and B in comparison to group C: 57 and 51 versus 67%, respectively. Hence, the sub-sunburn sunbed treatment was effective in tanning and increasing the 25(OH)D serum level, more so than 1000 IU per day, but had no appreciable effect on colds.

Vitamin D: emerging roles in infection and immunity

In the preantibiotic era, TB of the skin was treated successfully with UV light. By the 1920s, pulmonary TB was being treated with regular sun exposure. During the last decade, basic laboratory research into the antimicrobial actions of vitamin D has provided new insights into these historical observations. Vitamin D has a critical role in the innate immune system through the production of antimicrobial peptides - particularly cathelicidin. Vitamin D would appear to have an important role in respiratory tract, skin and potentially gut health. A number of autoimmune diseases, including multiple sclerosis, Type I diabetes, systemic lupus erythematosus and rheumatoid arthritis, are associated with vitamin D deficiency. Vitamin D could have an important role in the prevention and possible treatment of these conditions; however, much of the current evidence relates to basic science and epidemiological research. In many situations, appropriate double-blind, randomized controlled trial data to guide clinicians treating infectious and autoimmune disease is still lacking.

Vitamin D, innate immunity and upper respiratory tract infection

INTRODUCTION

At the turn of the twentieth century, ultraviolet light was successfully used to treat tuberculosis of the skin. Upper respiratory tract infections had been inversely associated with sun exposure. During the last decade, basic scientific research demonstrated that vitamin D has an important anti-infective role.

METHOD

Review of the relevant literature on the influence of vitamin D on innate immunity and respiratory tract infection.

RESULTS

Vitamin D is involved in the production of defensins and cathelicidin - antimicrobial peptides that provide a natural defence against potential microbiological pathogens. Vitamin D supplementation increases cathelicidin production. Low vitamin D levels are associated with an increased incidence of upper respiratory tract infections.

CONCLUSIONS

Vitamin D appears to play an important role in the regulation of innate immunity in the upper respiratory tract. Optimal vitamin D levels and appropriate dosing schedules have yet to be determined.

Prevalence of vitamin D deficiency among patients attending a general otolaryngology clinic in South Auckland

OBJECTIVES

We performed a prospective observational study to estimate the prevalence of vitamin D deficiency in patients attending a general otolaryngology clinic in South Auckland, New Zealand.

METHODS

From July 21,2008, to August 7, 2008, all new patients presenting to otolaryngology clinics at which one of the authors (D.R.) was present had their vitamin D status assessed by measurement of their plasma 25-hydroxyvitamin D [25(OH)D] level.

RESULTS

Of 48 patients, 2% had 25(OH)D levels of 17.5 nmol/L or less (a level associated with osteomalacia), 58% had 25(OH)D levels of 50 nmol/L or less (a level associated with vitamin D deficiency), and 100% had 25(OH)D levels of 80 nmol/L or less.

CONCLUSIONS

Most of the patients attending a general otolaryngology clinic in South Auckland are vitamin D-deficient. It is unclear whether low vitamin D levels are associated more directly with otolaryngological disorders or skin type, because the small size of this study and the broad range of conditions seen precluded a meaningful statistical analysis. Further research into the relationship of vitamin D to specific otolaryngological presentations is required.

Plasma 25-hydroxyvitamin D levels in young children undergoing placement of tympanostomy tubes

OBJECTIVES

We report the plasma 25-hydroxyvitamin D [25(OH)D] levels of 16 young children who were undergoing ambulatory surgery for placement of tympanostomy tubes.

METHODS

We previously obtained blood samples from young children who were undergoing ambulatory surgery and reported that they had lower blood levels than adults of eicosapentaenoic acid (an omega-3 fatty acid), vitamin A, and selenium. Plasma frozen continuously at -80 degrees C was available from 16 subjects who were undergoing placement of tympanostomy tubes.

RESULTS

The mean (+/- SD) age of the patients was 3.7 +/- 1.6 years (median, 2.9 years; range, 1.9 to 7.4 years). Sixty-two percent were male; half were white, and half were Hispanic. Sixty-two percent were private patients; the parents reported that half were taking vitamin supplements. None had a history of rickets. None had 25(OH)D levels less than 10 ng/mL; 50% had 25(OH)D levels less than 20 ng/mL (deficient in adults); another 31% had levels from 21 to 29 ng/mL (insufficient in adults).

CONCLUSIONS

Vitamin D is essential for the production of endogenous antimicrobial peptides, and has been linked to seasonal, epidemic influenza A. However, the level of 25(OH)D needed to prevent infection with various human pathogens has not been defined. In view of increasing bacterial resistance and emerging new pathogens, further research on the relationship of infection to 25(OH)D and other nutritional factors is warranted.

UV-induced immunosuppression in the balance

Around 1980, experiments with hairless mice showed us that UV-induced actinic keratoses (AK) and ensuing skin carcinomas did not arise independently: the rate of occurrence in one skin area was increased considerably if AKs had already been induced separately in another distant skin area, i.e. a systemic effect. The ground laying work of Margaret Kripke in the 1970s provided a fitting explanation: UV-induced immunosuppression and tolerance toward the UV-induced tumors. From Kripke's work a new discipline arose: "Photoimmunology." Enormous strides were made in exploring and expanding the effects from UV carcinogenesis to infectious diseases, and in elucidating the mechanisms involved. Stemming from concerns about a depletion of the ozone layer and the general impact of ambient UV radiation, the groups I worked in and closely collaborated with explored the anticipated adverse effects of UV-induced immunosuppression on healthy individuals. An important turning point was brought about in 1992 when the group of Kevin Cooper reported that immunosuppression could be induced by UV exposure in virtually all human subjects tested, suggesting that this is a normal and sound physiological reaction to UV exposure. This reaction could actually protect us from illicit immune responses against our UV-exposed skin, such as observed in idiopathic polymorphic light eruption. This premise has fruitfully rekindled the research on this common "sun allergy," affecting to widely varying degrees about one in five Europeans with indoor professions.

Epidemic influenza and vitamin D

In 1981, R. Edgar Hope-Simpson proposed that a 'seasonal stimulus' intimately associated with solar radiation explained the remarkable seasonality of epidemic influenza. Solar radiation triggers robust seasonal vitamin D production in the skin; vitamin D deficiency is common in the winter, and activated vitamin D, 1,25(OH)2D, a steroid hormone, has profound effects on human immunity. 1,25(OH)2D acts as an immune system modulator, preventing excessive expression of inflammatory cytokines and increasing the 'oxidative burst' potential of macrophages. Perhaps most importantly, it dramatically stimulates the expression of potent anti-microbial peptides, which exist in neutrophils, monocytes, natural killer cells, and in epithelial cells lining the respiratory tract where they play a major role in protecting the lung from infection. Volunteers inoculated with live attenuated influenza virus are more likely to develop fever and serological evidence of an immune response in the winter. Vitamin D deficiency predisposes children to respiratory infections. Ultraviolet radiation (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as does cod liver oil (which contains vitamin D). An interventional study showed that vitamin D reduces the incidence of respiratory infections in children. We conclude that vitamin D, or lack of it, may be Hope-Simpson's 'seasonal stimulus'.

No adaptation to UV-induced immunosuppression and DNA damage following exposure of mice to chronic UV-exposure

It is well known that ultraviolet (UV) radiation induces erythema, immunosuppression and carcinogenesis. We hypothesized that chronic exposure to solar UV radiation induces adaptation that eventually prevents the suppression of acquired immunity. We studied adaptation for UV-induced immunosuppression after chronic exposure of mice to a suberythemal dose of solar simulated radiation (SSR) with Cleo Natural lamps, and subsequent exposure to an immunosuppressive dose of solar or UVB radiation (TL12). After UV dosing, the mice were sensitized and challenged with either diphenylcyclopropenone (DPCP) or picryl chloride (PCl). To assess the adaptation induced by solar simulated radiation, we measured the proliferative response and cytokine production of skin-draining lymph node cells after immunization to DPCP, the contact hypersensitivity (CHS) response to PCl, and thymine-thymine (T-T) cyclobutane dimers in the skin of mice. After induction of immunosuppression by SSR or by TL12 lamps, the proliferative response of draining lymph node cells after challenge with DPCP, or the CHS after challenge with PCl, showed significant suppression of the immune response. Chronic irradiation from SSR preceding the immunosuppressive dose of UV failed to restore the suppressed immune response. Reduced lipopolysaccharide-triggered cytokine production (of IL-12p40, IFN-gamma, IL-6 and TNF-alpha) by draining lymph node cells of mice sensitized and challenged with DPCP indicated that no adaptation is induced. In addition, the mice were not protected from T-T dimer DNA damage after chronic solar irradiation. Our studies reveal no evidence that chronic exposure to low doses of SSR induces adaptation to UV-induced suppression of acquired immunity.

Circulating leukocyte and cytokine responses to measles and poliovirus vaccination in children after ultraviolet radiation exposures

Suberythemal ultraviolet radiation (UVR) exposures of children are used routinely in Russia to prevent rickets and to strengthen general health. The aim of the present study was to re-evaluate the effects of such a regime on immune responses as UVR is now recognised to suppress cell-mediated immunity in many animal models. Seventeen infants were immunised with attenuated measles and recall polio vaccines of whom 10 had been given a course of prophylactic UV exposures before the vaccinations. All the infants in the study developed an acute infectious conjunctivitis one week prior to the vaccinations and were convalescent at the time of the vaccination. They were bled on the day of the vaccinations and at several times thereafter to assess leukocyte percentages and plasma cytokine levels. On the day of the vaccinations, an active immune response was apparent. The UV-exposed children differed from the unexposed children by having a smaller percentage of natural killer cells and a higher percentage of CD25-positive cells. In the days following the vaccinations, the UV-exposed infants had a lowered percentage of total lymphocytes with increased percentages of monocytes, eosinophils, neutrophils and HLA-DR-positive cells as well as higher concentrations of plasma IL-1beta and IL-10 compared with the unexposed infants. There were no local or systemic clinical reactions to the vaccines in the UV-group while a moderate rise in temperature of three children in the unexposed group occurred. Thus the UV irradiations modulated leukocyte percentages and plasma cytokine levels following the vaccinations, perhaps through the activation of a T helper 2-like response.

Immune function testing of human pharmaceuticals: regulatory overshoot?

Suppression of the activity of the immune system can result in decreased resistance to (opportunistic) infection and cancer. Experimental animal studies have identified many immunotoxic agents, but data on unintended immuno-toxicity of human pharmaceuticals are limited. To enhance the sensitivity of the non-clinical screening of human pharmaceuticals, immunotoxicity endpoints in standard toxicity studies, as well as an immune function study, are requested by the EU, incorporating a T-cell-dependent antigen response in the first screening phase. Authorities from other areas in the world follow similar lines for immunotoxicity testing, but differ in whether or not the functional assay is seen as a primary requisite or can be secondary to other factors or observations. Based on a limited survey in the framework of the International Conference on Harmonization, the European position has been reconsidered to negotiate a broad cause-for-concern approach. The relevance of functional testing of the immune system to show effects of human pharmaceuticals is shown in this review. There is certainly a need for more in-depth testing of the integrity of the immune system and a cause-for-concern approach is, therefore, needed. A broad category is the number of compounds that might interact via binding to receptor sites at the broadly taken population of leukocytes (e.g., lymphocytes, macrophages). Criteria to differentiate among compounds in this category have yet to be ascertained.