Vitamin D, respiratory infections, and chronic disease: Review of meta-analyses and randomized clinical trials

BACKGROUND

Observational studies have suggested associations of vitamin D deficiency (VDD) with respiratory tract infections, impaired bone health, and myriad chronic diseases.

OBJECTIVE

To assess potential causal relationships between vitamin D supplementation and a reduced risk of these conditions, a review of the evidence across available meta-analyses of randomized control trials (RCTs) and RCTs was performed.

METHOD

PubMed, Embase, Cochrane Library, and Web of Science were searched from their inception to March 2021. We included only RCTs and meta-analyses of RCTs focusing on the association between vitamin D and respiratory disease, bone health, cardiovascular disease (CVD), diabetes mellitus, and cancer.

RESULTS

A total of 107 RCTs and 62 meta-analysis of RCTs were included. Although most RCTs did not support benefits of vitamin D supplementation, suggestive evidence for benefit was found in populations at greater risk of VDD and for acute respiratory infections, fractures in institutionalized older adults, type 2 diabetes among patients with prediabetes, and cancer mortality. In contrast, no compelling evidence for benefit was found for other respiratory conditions, fractures in community-dwelling adults, falls, cancer incidence, or CVD.

CONCLUSIONS

Current evidence from RCTs and meta-analyses of RCTs is inconsistent regarding the effects of vitamin D supplementation on respiratory infections and chronic diseases. Individuals most likely to benefit are those with baseline VDD or with selected high-risk conditions. Public health initiatives are needed to eliminate VDD globally, and future research will be enhanced by a 'precision prevention' approach to identify those most likely to benefit from vitamin D supplementation.

Hat, shade, long sleeves, or sunscreen? Rethinking US sun protection messages based on their relative effectiveness

BACKGROUND

Sun protection messages in the United States emphasize sunscreen use, although its efficacy in skin cancer prevention remains controversial.

METHODS

We used data from NHANES 2003-2006, restricted to adult whites (n = 3,052) to evaluate how Americans protect themselves from the sun. Participants completed questionnaires on the frequency with which they used sunscreen, wore a hat, long sleeves, or stayed in the shade, in addition to the number of sunburns in the past year.

RESULTS

Although using sunscreen is the most common sun protective behavior (30%), frequent sunscreen use was not associated with fewer sunburns. However, the odds of multiple sunburns were significantly lower in individuals who frequently avoided the sun by seeking shade (OR = 0.70, p < 0.001) or wearing long sleeves (OR = 0.73, p = 0.01).

CONCLUSIONS

Our findings suggest that shade and protective clothing may be more effective than sunscreen, as typically used by Americans.

Explaining multiple sclerosis prevalence by ultraviolet exposure: a geospatial analysis

BACKGROUND

Epidemiologic studies have shown a positive correlation of multiple sclerosis (MS) prevalence with latitude. However, there has not been a causal association found. Increased dietary intake and increased serum levels of vitamin D showed to be protective for the development of MS. Ultraviolet (UV) radiation plays an important role in vitamin D synthesis and could potentially explain both latitude differences in MS prevalence and the low levels of vitamin D in individuals with MS.

OBJECTIVE

To evaluate the relationship between UV radiation and MS prevalence using geospatial analysis.

METHODS

Geospatial analysis was performed on North American regions and separately for the continental United States. The correlation of UV radiation (measured as UV index [UVI]) versus MS prevalence and UV radiation versus case-control ratios was calculated. In addition, the relative risk (RR) of MS was determined for regions/states with low UV radiation exposure.

RESULTS

Case-control ratios by US state and MS prevalence by North American region showed a strong negative (inverse) correlation with UVI (R = -0.72 and -0.86, respectively). The RR for the five highest risk states/lowest UVI versus the five lowest risk states/highest UVI was increased (RR = 1.8-5.4). The RR for MS, when comparing North American regions with lowest and highest UVI, was 3.78 and within US regions was 1.52.

CONCLUSION

This analysis suggests a strong association between UV radiation and MS distribution, and an increase in risk for MS in those areas with a low UVI.