Imputating missing values in diary records of sun-exposure study

In a sun-exposure study, questionnaires concerning sunhabits were collected from 195 subjects. This paper focuses on the general problem of missing data values, which occurs when some, or even all of the questions have not been answered in a questionnaire. Here, only missing values of low concentration are investigated. We consider and compare two different models for imputating missing values: the Gaussian model and the non-parametric K-Nearest Neighbor model

A population-based cohort study on sun habits and endometrial cancer

Background:No large cohort study has examined the risk of endometrial cancer in relation to sun exposure.Methods:A population-based cohort study of 29 508 women who answered a questionnaire in 1990-92, of whom 24 098 responded to a follow-up enquiry in 2000-02. They were followed for an average of 15.5 years.Results:Among the 17 822 postmenopausal women included, 166 cases of endometrial cancer were diagnosed. We used a multivariate Cox regression analysis adjusting for age and other selected demographic variables to determine the risk of endometrial cancer. Women using sun beds >3 times per year reduced their hazard risk (HR) by 40% (0.6, 95% confidence interval (CI) 0.4-0.9) or by 50% when adjusting for body mass index or physical activity (HR 0.5, 95% CI 0.3-0.9), and those women who were sunbathing during summer reduced their risk by 20% (HR 0.8 95% CI 0.5-1.5) compared with women who did not expose themselves to the sun or to artificial sun (i.e., sun beds).Conclusion:Exposure to artificial sun by the use of sun beds >3 times per year was associated with a 40% reduction in the risk of endometrial cancer, probably by improving the vitamin D levels during winter.British Journal of Cancer advance online publication, 23 June 2009; doi:10.1038/sj.bjc.6605149 www.bjcancer.com

The Enigmatic N-Terminal Domain of Proglucagon; A Historical Perspective

Enteroglucagon refers to the predominant peptide with glucagon-like immunoreactivity (GLI) that is released by the intestine into the circulation in response to nutrients. Development of a radioimmunoassay for glucagon revealed issues that were not apparent in applications of the insulin radioimmunoassay. The fact that some antisera raised against glucagon recognized glucagon-related peptides in extracts of both pancreas and gut whereas others recognized only components in the pancreas remained a mystery until it was realized that the “gut GLI cross-reactive” antisera were directed against an epitope in the N-terminal to central region of glucagon whereas the “pancreatic glucagon specific” antisera were directed against an epitope in the C-terminal region. Unlike the cross-reactive antisera, the glucagon specific antisera did not recognize components in which glucagon was extended from its C-terminus by additional amino acids. Initial attempts to purify enteroglucagon from porcine ileum led to the erroneous conclusion that enteroglucagon comprised 100 amino acids with an apparent molecular mass of 12,000 Da and was consequently given the name glicentin. Subsequent work established that the peptide constituted residues (1-69) of proglucagon (Mr 8128). In the 40 years since the structural characterization of glicentin, attempts to establish an unambiguous physiological function for enteroglucagon have not been successful. Unlike the oxyntomodulin domain at the C-terminus of enteroglucagon, the primary structure of the N-terminal domain (glicentin-related pancreatic peptide) has been poorly conserved among mammals. Consequently, most investigations of the bioactivity of porcine glicentin may have been carried out in inappropriate animal models. Enteroglucagon may simply represent an inactive peptide that ensures that the intestine does not release equimolar amounts of a hyperglycemic agent (glucagon) and a hypoglycemic agent (GLP-1) after ingestion of nutrients

Novel approach to analysing large data sets of personal sun exposure measurements

Personal sun exposure measurements provide important information to guide the development of sun awareness and disease prevention campaigns. We assess the scaling properties of personal ultraviolet radiation (pUVR) sun exposure measurements using the wavelet transform (WT) spectral analysis to process long-range, high-frequency personal recordings collected by electronic UVR dosimeters designed to measure erythemal UVR exposure. We analysed the sun exposure recordings of school children, farmers, marathon runners and outdoor workers in South Africa, and construction workers and work site supervisors in New Zealand. We found scaling behaviour in all the analysed pUVR data sets. We found that the observed scaling changes from uncorrelated to long-range correlated with increasing duration of sun exposure. Peaks in the WT spectra that we found suggest the existence of characteristic times in sun exposure behaviour that were to some extent universal across our data set. Our study also showed that WT measures enable group classification, as well as distinction between individual UVR exposures, otherwise unattainable by conventional statistical methods

Photostability of commercial sunscreens upon sun exposure and irradiation by ultraviolet lamps

BACKGROUND: Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiation. The fact that some sunscreens are photounstable has been known for many years. Since the UV-absorbing ingredients of sunscreens may be photounstable, especially in the long wavelength region, it is of great interest to determine their degradation during exposure to UV radiation. Our aim was to investigate the photostability of seven commercial sunscreen products after natural UV exposure (UVnat) and artificial UV exposure (UVart). METHODS: Seven commercial sunscreens were studied with absorption spectroscopy. Sunscreen product, 0.5 mg/cm(2), was placed between plates of silica. The area under the curve (AUC) in the spectrum was calculated for UVA (320–400 nm), UVA1 (340–400 nm), UVA2 (320–340 nm) and UVB (290–320 nm) before (AUC(before)) and after (AUC(after)) UVart (980 kJ/m(2 )UVA and 12 kJ/m(2 )of UVB) and before and after UVnat. If theAUC Index (AUCI), defined as AUCI = AUC(after)/AUC(before), was > 0.80, the sunscreen was considered photostable. RESULTS: Three sunscreens were unstable after 90 min of UVnat; in the UVA range the AUCI was between 0.41 and 0.76. In the UVB range one of these sunscreens was unstable with an AUCI of 0.75 after 90 min. Three sunscreens were photostable after 120 min of UVnat; in the UVA range the AUCI was between 0.85 and 0.99 and in the UVB range between 0.92 and 1.0. One sunscreen showed in the UVA range an AUCI of 0.87 after UVnat but an AUCI of 0.72 after UVart. Five of the sunscreens were stable in the UVB region. CONCLUSION: The present study shows that several sunscreens are photounstable in the UVA range after UVnat and UVart. There is a need for a standardized method to measure photostability, and the photostability should be marked on the sunscreen product

Sun protection and sunbathing practices among at-risk family members of patients with melanoma

<p>Abstract</p> <p>Background</p> <p>Despite the increased level of familial risk, research indicates that family members of patients with melanoma engage in relatively low levels of sun protection and high levels of sun exposure. The goal of this study was to evaluate a broad range of demographic, medical, psychological, knowledge, and social influence correlates of sun protection and sunbathing practices among first-degree relatives (FDRs) of melanoma patients and to determine if correlates of sun protection and sunbathing were unique.</p> <p>Methods</p> <p>We evaluated correlates of sun protection and sunbathing among FDRs of melanoma patients who were at increased disease risk due to low compliance with sun protection and skin surveillance behaviors. Participants (<it>N </it>= 545) completed a phone survey.</p> <p>Results</p> <p>FDRs who reported higher sun protection had a higher education level, lower benefits of sunbathing, greater sunscreen self-efficacy, greater concerns about photo-aging and greater sun protection norms. FDRs who reported higher sunbathing were younger, more likely to be female, endorsed fewer sunscreen barriers, perceived more benefits of sunbathing, had lower image norms for tanness, and endorsed higher sunbathing norms.</p> <p>Conclusion</p> <p>Interventions for family members at risk for melanoma might benefit from improving sun protection self-efficacy, reducing perceived sunbathing benefits, and targeting normative influences to sunbathe.</p