Biomedical subjects

L Blizzard

Publications and source records attributed to L Blizzard.

At least 19 recordsLinked to original sources

PubMed2007

The association between non-melanoma skin cancer and osteoporotic fractures--a population-based record linkage study.

UNLABELLED: We studied the association between osteoporotic fractures and prior non-melanoma skin cancer (NMSC, a biomarker for cumulative sun exposure). The risk of prior NMSC in our fracture cohort was significantly reduced (standardised incidence ratio 0.69, 95% CI 0.61, 0.78). Adequate lifetime sun exposure may be necessary to protect against osteoporotic fractures in later life. INTRODUCTION: The relationship between cumulative sun exposure and osteoporotic fractures is uncertain. We aimed to study the association between non-melanoma skin cancer (NMSC), a marker of cumulative sun exposure, and osteoporotic fractures in an older cohort. METHODS: A retrospective cohort study in southern Tasmania in people aged at least 50 years with incident radiographic fracture (n = 2,283) was carried out. By record linkage to the Tasmanian Cancer Registry the cohort was followed backwards through time until the occurrence of NMSC or end-of follow-up. Relative risk was estimated by the standardised incidence ratio (SIR) using sex-, age- and calendar year-specific cancer incidence rates in southern Tasmania as reference. RESULTS: The incidence of prior NMSC in the fracture cohort was 31% lower than for the general population (SIR 0.69, 95% CI 0.61, 0.78). This effect was significant for most fracture subtypes except pelvic and wrist fractures and observed for both NMSC subtypes, squamous cell carcinoma and basal cell carcinoma. CONCLUSIONS: Older people with osteoporotic fractures may have had lifestyles linked to lower cumulative sunlight exposure. Achieving a balance between adequate lifetime sun exposure and protection against its adverse effects (such as fractures and skin cancer) may require assessment of individual risks.

Age Distribution↗

PubMed2006

Dual energy X-ray absorptiometry body composition and aging in a population-based older cohort.

OBJECTIVE: The aims of this cross-sectional study were (1) to examine the effect of age on body composition in older adults using dual-energy X-ray absorptiometry (DXA) and (2) to evaluate the agreement of DXA with standard indirect anthropometric measures (body mass index (BMI), waist circumference and waist-to-hip ratio (WHR)). RESEARCH METHODS AND PROCEDURES: A population-based sample of 731 adults aged between 50 and 79 years underwent measurement of BMI, waist circumference, WHR, DXA total body fat mass, DXA % total body fat, DXA % trunk fat and DXA lean body mass. Linear regression was used to test for trend in measures of body composition between age categories in men and women. Partial correlations and Bland-Altman analysis were used to examine the agreement of DXA measures with indirect measures. RESULTS: DXA lean body mass decreased significantly with increasing age in both sexes (P<0.05). In males, BMI (P=0.01) and body weight (P<0.01) decreased with age, and in females, WHR (P=0.05), DXA % total fat (P=0.02) and DXA % trunk fat (P=0.05) increased with age. There was good agreement between DXA measures of fatness and indirect anthropometric measures, except for WHR, which showed greater variability in its comparisons with DXA. CONCLUSION: Using the highly sensitive and direct DXA method of measuring body composition, a decline in lean body mass and an increase in adiposity was observed with aging. Except for WHR, indirect anthropometric measures generally showed high levels of agreement with DXA fat measures in this older cohort.

Absorptiometry, Photon↗

PubMed2006

Parameter estimation and goodness-of-fit in log binomial regression.

An estimate of the risk, adjusted for confounders, can be obtained from a fitted logistic regression model, but it substantially over-estimates when the outcome is not rare. The log binomial model, binomial errors and log link, is increasingly being used for this purpose. However this model's performance, goodness of fit tests and case-wise diagnostics have not been studied. Extensive simulations are used to compare the performance of the log binomial, a logistic regression based method proposed by Schouten et al. (1993) and a Poisson regression approach proposed by Zou (2004) and Carter, Lipsitz, and Tilley (2005). Log binomial regression resulted in "failure" rates (non-convergence, out-of-bounds predicted probabilities) as high as 59%. Estimates by the method of Schouten et al. (1993) produced fitted log binomial probabilities greater than unity in up to 19% of samples to which a log binomial model had been successfully fit and in up to 78% of samples when the log binomial model fit failed. Similar percentages were observed for the Poisson regression approach. Coefficient and standard error estimates from the three models were similar. Rejection rates for goodness of fit tests for log binomial fit were around 5%. Power of goodness of fit tests was modest when an incorrect logistic regression model was fit. Examples demonstrate the use of the methods. Uncritical use of the log binomial regression model is not recommended.

Algorithms↗

PubMed2006

Asthma onset prior to multiple sclerosis and the contribution of sibling exposure in early life.

Higher sibling exposure is associated with a reduced risk of asthma and other T helper 2 (Th2)-type disorders, possibly through a beneficial effect of higher infection load. The effect on Th1 disorders such as multiple sclerosis (MS) is less clear. Here we examine the association between asthma and MS, taking into account early life sibling exposure. A population-based case-control study in Tasmania, Australia based on 136 cases of magnetic resonance imaging (MRI)-confirmed MS and 272 community controls, matched on sex and year of birth. Study measures include cumulative exposure to total, older or younger siblings by age 6 years, history of doctor-diagnosed asthma and serological IgG responses to herpes viruses. MS cases were more likely (P = 0.02) than controls to have asthma which began before age of onset of MS symptoms compared to the corresponding age for controls. The absence of younger sibling exposure by age 6 years potentiated (P = 0.04) the association between asthma and MS. Compared to those with younger sibling exposure and no asthma, the adjusted odds ratio for MS for those with asthma and no younger sibling exposure was 7.22 (95% CI: 2.52, 20.65). Early life sibling exposure was associated with altered IgG serological responses to Epstein-Barr virus (EBV) and herpes simplex virus 1 (HSV1) in adulthood. Reduced early life sibling exposure appeared to contribute to the excess of asthma among MS cases by the time of MS onset. MS development may reflect factors that relate to a general immuno-inflammatory up-regulation of immune activity as well as disease specific factors. The link between early life sibling exposure and the immune response to herpes group viral antigens is consistent with a protective role for early life infections.

Adult↗

PubMed2006

Validity and reliability of adult recall of past sun exposure in a case-control study of multiple sclerosis.

BACKGROUND: Measurement of past sun exposure through recall by adults has the potential for measurement error. We aimed to investigate aspects of validity and reliability of self-reported past sun exposure. METHODS: A population-based case-control study was conducted in Tasmania on 136 cases with multiple sclerosis and 272 age- and sex-matched community controls. Repeat interviews on 52 cases and 52 controls were done on average 11 weeks after the initial interview. Sun exposure was assessed by questionnaire and lifetime calendar. Other measurements included serum 25-hydroxyvitamin D, actinic damage, and skin phenotype. RESULTS: There was an association between recent sun exposure and serum vitamin D (time in the sun: r = 0.22, P < 0.01; activities outside: r = 0.31, P < 0.01 for controls) and between lifetime sun exposure and actinic damage [correlation between 0.34 (P < 0.01) and 0.17 (P = 0.01) for controls]. The test-retest weighted kappa statistic of self-reported sun exposure ranged from 0.43 to 0.74. Recall of childhood/adolescent sun exposure by standardized questioning was no less reproducible than recall of recent adult sun exposure and no less reliable when made with the calendar method. Comparing the questionnaire and calendar method, the measures of childhood/adolescent sun exposure had a similar predictive validity for multiple sclerosis. CONCLUSIONS: The results of this study provide further evidence that adults are able to recall past sun exposure with shown validity and reliability and present information about the possible reasons for the good reliability of recalled sun exposure measures.

Adolescent↗

PubMed2004

Measuring environmental factors can enhance the search for disease causing genes?

The value of the concurrent measurement of environmental factors in studies aimed at the discovery of disease causing genes has been questioned on the grounds that such an approach fails to increase study power. This report discusses the issue and shows with examples from the recent literature that the examination of a gene disease association within an environmental subgroup can provide enhanced opportunities for detecting gene effects. The concurrent collection of environmental as well as genetic factors in studies of disease aetiology may enhance study informativeness and validity in several ways, including an increase in the power of the study to detect gene disease associations.

Birth Weight↗

PubMed2004

Symptoms and medical conditions in Australian veterans of the 1991 Gulf War: relation to immunisations and other Gulf War exposures.

AIMS: To investigate whether Australian Gulf War veterans have a higher than expected prevalence of recent symptoms and medical conditions that were first diagnosed in the period following the 1991 Gulf War; and if so, whether these effects were associated with exposures and experiences that occurred in the Gulf War. METHODS: Cross-sectional study of 1456 Australian Gulf War veterans and a comparison group who were in operational units at the time of the Gulf War, but were not deployed to that conflict (n = 1588). A postal questionnaire was administered and the likelihood of the diagnosis of self-reported medical conditions was assessed and rated by a medical practitioner. RESULTS: Gulf War veterans had a higher prevalence of all self-reported health symptoms than the comparison group, and more of the Gulf War veterans had severe symptoms. Increased symptom reporting was associated with several exposures, including having more than 10 immunisations, pyridostigmine bromide tablets, anti-biological warfare tablets, pesticides, insect repellents, reportedly being in a chemical weapons area, and stressful military service experiences in a strong dose-response relation. Gulf War veterans reported psychological (particularly post-traumatic stress disorder), skin, eye, and sinus conditions first diagnosed in 1991 or later more commonly than the comparison group. Over 90% of medical conditions reported by both study groups were rated by a medical practitioner as having a high likelihood of diagnosis. CONCLUSION: More than 10 years after the 1991 Gulf War, Australian veterans self-report all symptoms and some medical conditions more commonly than the comparison group. Further analysis of the severity of symptoms and likelihood of the diagnosis of medical conditions suggested that these findings are not due to over-reporting or to participation bias.

Adult↗

PubMed2003

Past exposure to sun, skin phenotype, and risk of multiple sclerosis: case-control study.

OBJECTIVE: To examine whether past high sun exposure is associated with a reduced risk of multiple sclerosis. DESIGN: Population based case-control study. SETTING: Tasmania, latitudes 41-3 degrees S. PARTICIPANTS: 136 cases with multiple sclerosis and 272 controls randomly drawn from the community and matched on sex and year of birth. MAIN OUTCOME MEASURE: Multiple sclerosis defined by both clinical and magnetic resonance imaging criteria. RESULTS: Higher sun exposure when aged 6-15 years (average 2-3 hours or more a day in summer during weekends and holidays) was associated with a decreased risk of multiple sclerosis (adjusted odds ratio 0.31, 95% confidence interval 0.16 to 0.59). Higher exposure in winter seemed more important than higher exposure in summer. Greater actinic damage was also independently associated with a decreased risk of multiple sclerosis (0.32, 0.11 to 0.88 for grades 4-6 disease). A dose-response relation was observed between multiple sclerosis and decreasing sun exposure when aged 6-15 years and with actinic damage. CONCLUSION: Higher sun exposure during childhood and early adolescence is associated with a reduced risk of multiple sclerosis. Insufficient ultraviolet radiation may therefore influence the development of multiple sclerosis.

Adolescent↗

PubMed2002

Syndrome X in 8-y-old Australian children: stronger associations with current body fatness than with infant size or growth.

OBJECTIVE: Syndrome X (clustering of insulin resistance, dyslipidaemia and hypertension) in adults with central obesity has been suggested to be a consequence of poor foetal development. We investigated clustering of syndrome X factors in a sample of 8-y-old Australian children, and whether the clusters were associated with size at birth and childhood obesity. DESIGN: Longitudinal, 1997 follow-up of children enrolled as singleton-born neonates in 1989. SUBJECTS: A total of 298 healthy Australian children (208 boys, 90 girls, age range 7.4-8.9 y). MEASUREMENTS: Anthropometry at birth and at 4 weeks. In 1997, at 8 y of age: fasting insulin and glucose, total and HDL-cholesterol, triglycerides and blood pressure. RESULTS: Adverse levels of insulin and glucose, cholesterol and triglycerides co-existed more often than expected by chance (P<0.01). Three factors were identified in factor analysis: one loading on systolic and diastolic blood pressure ('blood pressure'); a second loading on insulin and glucose ('insulin resistance'); and a third loading negatively on HDL-cholesterol and positively on triglycerides ('dyslipidaemia'). The blood pressure factor was correlated with fatness at age 8 y (eg fat mass estimated from skin folds, r=0.11) and, after adjustment for current size, with birth weight (r=-0.15). Fat mass was also correlated with both 'insulin resistance' (r=0.24) and 'dyslipidaemia' (r=0.19). The increase in 'insulin resistance' (P=0.03) and 'dyslipidaemia' (P<0.01) per category of fat mass was greatest for subjects with higher-than-median subscapular-to-triceps ratio of skin folds. Neither 'insulin resistance' nor 'dyslipidaemia' was associated with anthropometry at birth. CONCLUSIONS: The Syndrome X risk variables clustered among children who had a tendency to deposit fat on the trunk. There was no evidence in this sample that infant size predicts development of the insulin resistance or dyslipidaemic components of the syndrome by age 8.

Adipose Tissue↗

PubMed2001

Declining lung cancer mortality of young Australian women despite increased smoking is linked to reduced cigarette 'tar' yields.

Lung cancer data were examined to determine whether the mortality rates of young Australian women have continued to increase in line with the proportions of them who have smoked tobacco. Trends in annual age-specific lung cancer mortality were estimated for 1965-1998. Age-specific mortality rates and age-adjusted ratios of mortality rates were calculated for birth cohorts. Proportions of smokers in those cohorts were estimated from results of eight national surveys of smoking, and their mean ages of commencement and years of smoking were assessed from surveys of smokers in two states. Lung cancer mortality rates of 20-44-year-old Australian women peaked in 1986. Age-adjusted mortality rates are lower for women born in the 1950s and 1960s than for women born in the 1940s, despite higher proportions of smokers, younger age of commencement and longer duration of smoking by age 30 years in the more recent cohorts. Increased smoking has not resulted in higher lung cancer mortality for Australian women born in the 1950s and 1960s. Reductions in tar yields of Australian-made cigarettes, which would have affected primarily those born after the 1940s, may be responsible.

Adult↗

PubMed2001

Regional variation in multiple sclerosis prevalence in Australia and its association with ambient ultraviolet radiation.

The aim of this study was to conduct an ecological analysis of the extent to which ultraviolet radiation (UVR) levels might explain the regional variation of multiple sclerosis (MS) in Australia. MS prevalence data for six Australian regions were compared with UVR levels of the largest city in each region, with some other climatic variables and with the melanoma incidence in the same regions. A close association was found between the theoretical MS prevalence predicted from UVR levels and the actual prevalence. Furthermore, the negative correlation between UVR and MS prevalence (r = -0.91, p = 0.01) was higher than the positive correlation observed for UVR and malignant melanoma incidence (r = 0.75, p = 0.15 for males and r = 0.80, p = 0.10 for females). This study demonstrated that the regional variation in MS prevalence in the continent of Australia could be closely predicted by regional UVR levels. It is consistent with the hypothesis that UVR exposure may reduce the risk of MS possibly via T-lymphocyte-mediated immunosuppression. Analytical epidemiology studies are required to investigate this specific hypothesis.

Adult↗

PubMed2000

Validity of a measure of the frequency of headaches with overt neck involvement, and reliability of measurement of cervical spine anthropometric and muscle performance factors.

OBJECTIVE: To test the validity of a questionnaire to measure frequency of headaches related to the neck. A secondary goal was to test the reliability of field measurement of associated cervical spine anthropometric and muscle performance factors. DESIGN: Intermethod and test-retest comparisons. SETTING: Two municipalities in a rural area of Tasmania, Australia. PARTICIPANTS: One hundred subjects were selected as a representative sample of never-injured adults from a comprehensive listing of the source population, and 93 participated. MAIN OUTCOME MEASURES: Subjects distinguished headaches matching three criteria for overt neck involvement, reported past-month frequency by questionnaire, and recorded in a diary occurrences during the next month. Measurements of height, weight, neck column length and circumference, lateral flexion and extension range of movement, cervical short flexor muscle endurance, and cervical long flexor and extensor strength were taken at the start and end of the month. RESULTS: Headache frequency was associated with neck stiffness and neck ache. There was moderate agreement (weighted K = .66) between questionnaire and diary, but better agreement (K = .72) for subjects who maintained their usual patterns of recreational sport. For this group, the correlation with "true" frequency was r(u) = .87. The anthropometric and muscle performance factors were reliably measured (intraclass correlations .96 to 1.00, kappa .78 to .86) despite minor improvement in muscle performance on retest. CONCLUSIONS: The questionnaire measure has construct validity. Neck-related headaches are a temporally stable presentation in never-injured subjects who maintain customary sporting activity. Measurement error was consequential, but less so for this group than for the study subjects generally. The anthropometric and muscle performance measurements were reliable, but slight improvements on retest suggest the need for multiple measurements.

Adult↗

PubMed2000

Melanin density and melanin type predict melanocytic naevi in 19-20 year olds of northern European ancestry.

Recent advances in estimating the density of cutaneous melanin by spectrophotometry and the concentration of the two types of melanin (eumelanin and phaeomelanin) in hair offer the potential to define the risk of skin cancer in individuals more accurately. The presence of common melanocytic naevi on the arm is associated with an increased risk of melanoma, and in this study the associations of arm naevi with melanin density at the upper inner arm and with melanin type in hair samples were examined in a representative sample (n = 267) of 19-20 year olds of northern European ancestry. Particularly in men, the association with naevus count was stronger for cutaneous melanin density than for follicular melanin type. Adjusted for recreational sun exposure, the rank correlation coefficients were r = -0.25, 0.12 and 0.01 for men, and r = -0.17, -0.12 and 0.14 for women, for cutaneous melanin, hair eumelanin and hair phaeomelanin, respectively. The associations with less objective markers of phenotype (hair colour, eye colour, nurse-assessed skin colour, and self-reported skin reaction to unaccustomed sun) were weaker. These findings provide important new information that human susceptibility to mutations of melanocytes can be estimated by objective biological measures. The next step is to determine whether these measures also predict the risk of melanoma.

Adolescent↗

PubMed2000

Mode of delivery and childhood blood pressure.

A number of studies have shown that children born by cesarean section have lower blood pressure during the neonatal period. The aim of this study was to investigate whether mode of delivery influenced childhood blood pressure: at age 7.5 to 8 y in a cohort of 756 children born preterm, at 7 to 9 y in a pilot study of 166 children born at term in the United Kingdom, and in a cohort of 650 Tasmanian children born at term. In the preterm cohort, systolic blood pressure was significantly lower in children born by cesarean section rather than delivered vaginally (99.3+/-10.0 versus 101.4+/-9.4 mm Hg; 95% confidence interval, -0.69 to -3.46; p = 0.003), with a significant trend to having a higher pressure in those born by breech versus forceps versus spontaneous vaginal delivery versus cesarean section. These findings were not replicated in the term cohorts. This raises the hypothesis that there is a sensitive period for programming later blood pressure by factors associated with mode of delivery and that this period does not extend to full-term.

Blood Pressure↗

PubMed1999

Within pair association between birth weight and blood pressure at age 8 in twins from a cohort study.

OBJECTIVES: To study the association between birth weight and blood pressure in children from multiple pregnancies (multiplets), mostly twins, to determine whether maternal or genetic factors are responsible for the association. DESIGN: Cohort study. SETTING: Southern Tasmania. SUBJECTS: 888 children including 104 multiplets (32 monozygotic, 72 dizygotic). MAIN OUTCOME MEASURE: Systolic blood pressure (mm Hg). RESULTS: Blood pressure decreased with birth weight and increased with current body mass. After adjustment for age and body mass, systolic blood pressure changed by -1.94 mm Hg (95% confidence interval -2.89 to -0.98) per 1 kg increase in birth weight of singletons. For multiplets, blood pressure changed by -7.0 mm Hg (-10.1 to -3.9) for each 1 kg increase in birth weight. This was little altered in within pair analyses (-5.3, -13.8 to 3.2) and was similar for both monozygotic (-6.5, -22.5 to 9.4) and dizygotic (-4.9, -15.8 to 6.0) pairs. CONCLUSION: Because the association between birth weight and blood pressure was largely unchanged in within pair analyses, exposures originating in the mother (such as nutritional status) cannot be wholly responsible. The association also remained within monozygotic pairs, suggesting that genetic predisposition is not wholly responsible either. The principal causal pathway must concern mechanisms within the fetoplacental unit. The stronger association in multiplets suggests that factors adversely influencing both blood pressure and birth weight are more prevalent in multiple pregnancies.

Birth Weight↗

PubMed1999

Frequency of headaches associated with the cervical spine and relationships with anthropometric, muscle performance, and recreational factors.

OBJECTIVE: To investigate headache specifically associated with the cervical spine, and factors associated with it. DESIGN: Cross-sectional, population-based observational study. SETTING: Two agriculturally based municipalities in southern Tasmania, Australia. PATIENTS: Four hundred fifty adults were randomly selected from electoral rolls; after refusals and exclusions, 427 subjects participated. OUTCOME MEASURE: For analysis, subjects were divided into three groups: those who did not have a particular type of headache in the previous month, those reporting fewer than two headaches of this type for the month (occasional headache), and those reporting two or more (frequent) headaches of this type in the month. STUDY FACTORS: Information collected by questionnaire and by objective measurement on anthropometric and functional measurements, wearing glasses or dentures, usual occupation, and usual recreational activities. RESULTS: The monthly prevalence of frequent headaches associated with the cervical spine was 28.3% (95% confidence interval [CI], 24.2-32.9), and another 35.4% (30.9-40.1) of subjects had these headaches occasionally. The frequency of headache occurrence was associated with a difference between front and back neck length of 2 cm or more. Occasional participation in recreational sport by men and wearing glasses by women were significant predictors of headache. CONCLUSION: Headaches of this type were more frequent in subjects with a long anterior neck length relative to their posterior neck length, particularly if they occasionally participated in recreational sports (men) or wore glasses (women).

Adult↗

PubMed1998

Bicycle injuries: road trauma is not the only concern.

Data on bicycle injury presentations at a public hospital emergency department for 1991-95 inclusive were analysed to determine the nature and extent of bicycle injuries in the community. There were 599 bicycle injury presentations during the study period, representing more than 2.0% of all injury-related presentations to the emergency department. The main outcome measures were severity and type of injury. Distribution by gender, age, helmet use (1991 and 1992 only), location and mechanism was examined. Rider-only injuries (falls or collisions with stationary objects) accounted for 79.3% of all presentations with only 5.2% due to collisions on a public road or footpath with other moving traffic. Of all injuries where a location was determined, 61.6% occurred in off-road locations. There was little difference in the overall proportions of hospital admissions from injuries on-road (12.4%) and off-road (9.0%). Cyclists injured in on-road collisions with traffic had a higher proportion of hospital admissions (40.0%) than those injured on-road by other mechanisms (7.6%). Children under 10 years of age who had been riding without a helmet suffered a much higher proportion of injuries to the head (53.2% of all injuries) than older cyclists riding without a helmet (19.4%). The majority (83.1%) of head injuries in children under 10 years of age occurred off-road and helmet use was lowest in this group (28.6%). Given previous evidence that helmet use can prevent head injuries, strategies to increase helmet use among cyclists, particularly young children, while riding both on and off-road, should be given a high priority. Rider-only injuries are also an important public health issue.

Accidents, Traffic↗

PubMed1998

The use of spectrophotometry to estimate melanin density in Caucasians.

The density of cutaneous melanin may be the property of the skin that protects it from damage by solar radiation, but there is not an accepted, noninvasive method of measuring it. To determine whether the density of cutaneous melanin can be estimated from reflectance of visible light by the skin, reflectance of 15-nm wavebands of light by the skin of the inner upper arm of each of 82 volunteers was measured at 20-nm intervals with a Minolta 508 spectrophotometer. A 3-mm skin biopsy was then taken from the same site, and four nonserial sections of it were stained with Masson Fontana for melanin. The melanin content of the basal area was calculated using the NIH Image analysis system. We show that cutaneous melanin in Caucasians can be estimated by the difference between two measurements of reflectance of visible light by the skin: those at wavelengths 400 and 420 nm. This new spectrophotometric measurement was more highly correlated (r = 0.68) with the histological measurements of cutaneous melanin than was skin reflectance of light of wavelength 680 nm (r = 0.33). Reflectances in the range of 650-700 nm have been used previously in skin cancer research. This relatively accurate measurement of melanin is quick and noninvasive and can be readily used in the field. It should provide improved discrimination of individual susceptibility to epidermal tumors in Caucasians and information about melanin's biological role in the causation of skin cancer.

Adult↗