Role of the renal nerves in blood pressure in male and female SHR

Female spontaneously hypertensive rats (SHR) have lower blood pressures than males. The renin-angiotensin system plays an important role in the sexual dimorphism of blood pressure in SHR. The sympathetic nervous system can stimulate renin release, and, therefore, the present study was performed to determine whether the renal sympathetic nerves play a role in the sexual dimorphism of blood pressure in SHR. Male and female SHR underwent bilateral kidney denervation or sham surgery, and, 2 wk later, mean arterial pressure (MAP) and pulse interval were recorded, and baroreflex sensitivity (BRS) was measured by the sequence technique. Left ventricle index (LVI) was also calculated. MAP was higher in sham-operated males than females (182 +/- 5 vs. 169 +/- 4 mmHg; P < 0.01), but, despite the higher MAP in males, LVI was significantly greater in female rats. BRS was not different between sham-operated male and female SHR. Following bilateral renal denervation, MAP was decreased by a similar percentage (8-10%) in males (169 +/- 2 mmHg) and females (152 +/- 3 mmHg), whereas LVI was reduced only in female SHR. BRS was not altered by renal denervation in either sex. These data indicate that renal nerves play a role in the control of blood pressure in SHR independent of sex, but do not play a role in mediating the sex differences in blood pressure.

Regression models for twin studies: a critical review

Twin studies have long been recognized for their value in learning about the aetiology of disease and specifically for their potential for separating genetic effects from environmental effects. The recent upsurge of interest in life-course epidemiology and the study of developmental influences on later health has provided a new impetus to study twins as a source of unique insights. Twins are of special interest because they provide naturally matched pairs where the confounding effects of a large number of potentially causal factors (such as maternal nutrition or gestation length) may be removed by comparisons between twins who share them. The traditional tool of epidemiological 'risk factor analysis' is the regression model, but it is not straightforward to transfer standard regression methods to twin data, because the analysis needs to reflect the paired structure of the data, which induces correlation between twins. This paper reviews the use of more specialized regression methods for twin data, based on generalized least squares or linear mixed models, and explains the relationship between these methods and the commonly used approach of analysing within-twin-pair difference values. Methods and issues of interpretation are illustrated using an example from a recent study of the association between birth weight and cord blood erythropoietin. We focus on the analysis of continuous outcome measures but review additional complexities that arise with binary outcomes. We recommend the use of a general model that includes separate regression coefficients for within-twin-pair and between-pair effects, and provide guidelines for the interpretation of estimates obtained under this model.

Vitamin D insufficiency in adolescent males in Southern Tasmania: prevalence, determinants, and relationship to bone turnover markers

There are limited data on vitamin D insufficiency in healthy children. The aim of this study was to describe the prevalence and determinants of vitamin D insufficiency and its association with bone turnover in adolescent boys (N = 136, mean age 16 years). Sun exposure and physical activity were assessed by questionnaire. Vitamin D stores were assessed by serum 25-hydroxyvitamin D3 (25[OH]D3). Bone turnover was assessed by bone-specific alkaline phosphatase (BAP) and urinary pyridinoline (PYR) to creatinine (Cr) ratio (mmol PYR/micromol Cr). The mean 25(OH)D3 level was low (44 nmol/l; 68% < 50 nmol/l; range, 16-87) and was associated with self-reported sun exposure on winter weekends (r = 0.23, p = 0.01), school holidays (r = 0.22, p = 0.01), and weekdays (r = 0.17, p = 0.05). It was also associated with number of sports (r = 0.34, p < 0.001) and vigorous activity (r = 0.22, p = 0.01) but not television, computer, and video watching (r = -0.04, p = 0.68). In multivariate analysis, number of sports but not total sun exposure remained significantly associated with 25(OH)D3. Furthermore, 25(OH)D3 was significantly associated with BAP in cutpoint analysis (cutpoint 55 nmol/l, p = 0.03) but not continuous analysis (r = -0.12, p = 0.16) and PYR in both forms (r = -0.23, p = 0.01, cutpoint 43 nmol/l, p = 0.01). In conclusion, vitamin D insufficiency is common in healthy adolescent boys in winter in our setting, is primarily derived from sports-related sun exposure, and is associated with bone turnover markers. These data suggest that a 25(OH)D3 level of at least 43-55 nmol/l is required for optimal bone health in children.

A differing pattern of association between dietary fish and allergen-specific subgroups of atopy

BACKGROUND

We examined the role of fish intake in the development of atopic disease with particular reference to the possibility of differential effects on allergen-specific subgroups of sensitization.

METHODS

The exposure of interest was parental report of fish intake by children aged 8 years at the 1997 Childhood Allergy and Respiratory Health Study (n = 499). The outcomes of interest were subgroups of atopy: house dust mite (HDM)-pure sensitization [a positive skin-prick test (SPT) > or = 2 mm to Der p or Der f only], ryegrass-pure sensitization (a positive SPT > or = 2 mm to ryegrass only); asthma and hay fever by allergen-specific sensitization.

RESULTS

A significant association between fish intake and ryegrass-pure [adjusted odds ratio (AOR) 0.37 (0.15-0.90)] but not HDM-pure sensitization [AOR 0.87 (0.36-2.13)] was found. Fish consumption significantly decreased the risk for ryegrass-pure sensitization in comparison with HDM-pure sensitization [AOR 0.20 (0.05-0.79)].

CONCLUSIONS

We have demonstrated a differential effect of fish intake for sensitization to different aeroallergens. This may be due to the different timing of allergen exposure during early life. Further investigation of the causes of atopic disease should take into account allergen-specific subgroups.

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.

War-related psychological stressors and risk of psychological disorders in Australian veterans of the 1991 Gulf War

BACKGROUND

Questions remain about the long-term health impacts of the 1991 Gulf War on its veterans.

AIMS

To measure psychological disorders in Australian Gulf War veterans and a military comparison group and to explore any association with exposure to Gulf War-related psychological stressors.

METHOD

Prevalences of DSM-IV psychological disorders were measured using the Composite International Diagnostic Interview. Gulf War-related psychological stressors were measured using a service experience questionnaire.

RESULTS

A total of 31% of male Gulf War veterans and 21% of the comparison group met criteria for a DSM-IV disorder first present in the post-Gulf War period. The veterans were at greater risk of developing post-Gulf War anxiety disorders including post-traumatic stress disorder, affective disorders and substance use disorders. The prevalence of such disorders remained elevated a decade after deployment. The findings can be explained partly as a 'war-deployment effect'. There was a strong dose-response relationship between psychological disorders and number of reported Gulf War-related psychological stressors.

CONCLUSIONS

Service in the 1991 Gulf War is associated with increased risk of psychological disorders and these are related to stressful experiences.

A prospective association between cocoon use in infancy and childhood asthma

There is increasing evidence for a role for bedding items in the development of asthma. The use of some forms of synthetic bedding, such as foam mattresses and pillows, is associated with a significantly increased risk of childhood wheeze. Our aim was to examine prospectively whether the use of synthetic cocoon/baby nests in infancy is associated with the subsequent development of wheeze in childhood. Data collected in 1988 as part of the Tasmanian Infant Health Survey were linked to the cross-sectional Childhood Asthma Survey conducted in 1995 in Tasmania, Australia. We were able to match 863 records out of the 1111 in the 1988 survey. Information including parental, child-care, and the infant's sleeping environment was collected at home interview in 1988 when the infant was 1 month of age. Data including sleep environment and asthma symptoms were available for each child at age 7 years. A generalised linear model was used to calculate the adjusted relative risk (RR) estimates for symptoms of wheeze and infant cocoon use. For children who were placed in a cocoon in infancy, there was an increased risk of recent wheeze (adjusted RR = 4.33 [95% CI 2.08, 9.02]) and night wheeze (adjusted RR = 3.35 [95% CI 1.52, 7.39]) at age 7 years. In view of the increasing prevalence of childhood asthma, the identification of potentially modifiable environmental factors which might operate in infancy is of importance. The present findings implicate infant bedding choice as a significant factor and further studies on the infant sleeping environment are indicated.

Trends in diabetes management practices of patients from an Australian insulin-treated diabetes register

AIMS

To compare diabetes management practices in 2001 among individuals from Tasmania, Australia, with a previous management survey conducted in 1995-7.

METHODS

Subjects were ascertained through the Tasmanian Insulin-Treated Diabetes Register. General demographic data were collected by telephone interview, and participants mailed a questionnaire on their diabetes management practices.

RESULTS

The response rate in 2001 was 80.8% (n=1336). There was a trend to more frequent blood glucose self-monitoring, notably in those less than 25 years (P<0.001 for monitoring >2 times/day), together with continued uptake of the pen system of insulin administration. More intensive shared management by general practitioner and diabetes specialist was noted, including a greater proportion visiting their doctor more than five times per year (P=0.006 for those <50 years). Most patients continue to be appropriately screened for hypertension and retinopathy. Dietitian visits declined overall (P=0.03 for at least annual visits), and there appeared to be an inadequate level of foot examination by patients and doctors.

CONCLUSIONS

The survey indicated that most patients were taking greater responsibility for their metabolic control, and intensive management practices and more convenient methods of administration may be contributors. Two areas of possible concern are access to dietitian services, and patient and health provider education on appropriate foot care.

Studies of Twins: Can they Shed Light on the Fetal Origins of Adult Disease Hypothesis?

There has been much interest in evidence that people with lower birthweight have higher risk of adult cardiovascular disease, but the causal pathways underlying such observations are uncertain. Study of twins offers an opportunity to shed light on these pathways, in three different ways. First, in a twin pregnancy maternal nutritional resources and the "supply line" to the fetuses will be more "stretched". We hypothesise that study of twin pregnancies is a more efficient way to identify modifiable maternal factors that influence later health than studies of singleton pregnancies. Second, twins have lower birthweight than singletons. Comparison of cardiovascular disease risk in twins versus that in singletons will provide insight into whether birthweight per se is in the underlying causal pathway of interest, and whether factors constraining fetal growth of twins (versus singletons) affect later outcome. Third, twin cohorts provide an opportunity to investigate the role of "shared" factors versus factors affecting each individual fetus, by comparing results of within-cohort versus within-pair analyses. Generalisability of findings in twins is debated. We suggest that findings in monochorionic twins (or in the absence of chorionicity data, those from monozygotic twins) need to be interpreted with caution.

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.

An association between plastic mattress covers and sheepskin underbedding use in infancy and house dust mite sensitization in childhood: a prospective study

BACKGROUND

Higher house dust mite (HDM) allergen exposure during infancy has been associated with increased HDM sensitization. Infant bedding has been associated with the accumulation of varying levels of HDM. Prospective data on the relationship between infant bedding and the development of HDM sensitization has not been previously examined.

OBJECTIVES

To determine if particular types of bedding used in infancy are associated with increased risk of house dust mite sensitization in childhood.

METHODS

A population-based sample (n = 498) of children born in 1988 or 1989, and who were resident in Northern Tasmania in 1997, participated in this study. These children were part of a birth cohort study (1988-95), the Tasmanian Infant Health Survey. Data on infant underbedding and mattresses was available on 460 and 457 children, respectively. The main outcome measure was HDM sensitization defined as a skin prick test (SPT) reaction of 3 mm or more to the allergens of Dermatophagoides pteronyssinus and/or Dermatophagoides farinae.

RESULTS

The use of either sheepskin underbedding or plastic mattress covers in infancy was associated with an increased risk of sensitization to HDM allergens at age 8 years. The adjusted risk ratio (RR) for sensitization to HDM with sheepskin in infancy was 2.27 (95% CI: 1.14, 4.55), P = 0.020. The adjusted RR for sensitization to HDM with the use of plastic mattress covers in infancy was 2.06 (95% CI: 1.22, 3.51), P = 0.007. The use of a foam mattress in infancy was not related to subsequent HDM sensitization.

CONCLUSION

Infant's bedding plays a role in the development of HDM sensitization in childhood. Intervention studies to examine mite allergen levels and the role of underbedding on the development of HDM sensitization are required.

Concentration of solutes in the renal inner medulla: interstitial hyaluronan as a mechano-osmotic transducer

Although the concentrating process in the renal outer medulla is well understood, the concentrating mechanism in the renal inner medulla remains an enigma. The purposes of this review are fourfold. 1) We summarize a theoretical basis for classifying all possible steady-state inner medullary countercurrent concentrating mechanisms based on mass balance principles. 2) We review the major hypotheses that have been proposed to explain the axial osmolality gradient in the interstitium of the renal inner medulla. 3) We summarize and expand on the Schmidt-Nielsen hypothesis that the contractions of the renal pelvocalyceal wall may provide an important energy source for concentration in the inner medulla. 4) We discuss the special properties of hyaluronan, a glycosaminoglycan that is the chief component of a gel-like renal inner medullary interstitial matrix, which may allow it to function as a mechano-osmotic transducer, converting energy from the contractions of the pelvic wall to an axial osmolality gradient in the medulla. These considerations set the stage for renewed experimental investigation of the urinary concentrating process and a new generation of mathematical models of the renal concentrating mechanism, which treat the inner medullary interstitium as a viscoelastic system rather than a purely hydraulic system.

A randomized controlled trial of phytoestrogen supplementation, growth and bone turnover in adolescent males

OBJECTIVE

To assess the effect of phytoestrogens on bone turnover and growth in adolescent boys.

DESIGN

Randomized double-blind placebo-controlled trial.

SETTING

Single school in northwest Tasmania.

PARTICIPANTS

Adolescent boys (treatment n=69, placebo n=59, mean age 16.8 y).

INTERVENTIONS

Six weeks of isoflavone supplementation (Novasoy, 50 mg daily of isoflavone equivalents). Bone turnover markers (bone specific alkaline phosphatase (BAP) and pyridinoline creatinine ratio (PYR)) were measured at baseline and follow-up.

RESULTS

Despite marked increases in urinary genistein and daidzein in the treatment arm (both P<0.001), there were no significant differences in BAP, PYR or short-term height or weight change. This applied to both intention-to-treat and per protocol analysis. Neither was there a significant correlation between urinary genistein and daidzein levels and BAP or PYR.

CONCLUSIONS

Phytoestrogen supplementation to the level of usual Japanese dietary intake has no measurable effect on bone turnover in adolescent boys. Longer-term studies of bone density may be desirable but it is unlikely that there will be a large effect in either girls or boys given the lower endogenous oestrogen levels in boys.

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.

Quantifying the change of melanoma incidence by Breslow thickness

Melanoma incidence has increased throughout the world over the past 25 years. A surrogate for the severity of melanoma is the Breslow thickness of the lesions. Data on melanoma, including Breslow thickness, were collected in 1978-1980 and 1988-1990 from the Tasmania Tumor Registry. We use a density ratio model to quantify the change of melanoma by Breslow thickness. In this model, the ratio of two densities is assumed to have a known form up to a parameter, but the underlying densities are not modeled. This model includes the length bias sampling model as a special case. The Kolmogorov-Smirnov test statistic is used to test the correctness of the density ratio model. Model-based cumulative distribution estimation is studied. Methodology developed in this article is applied to the Tasmania Tumor Registry data.

The rising prevalence of diabetes and impaired glucose tolerance: the Australian Diabetes, Obesity and Lifestyle Study

OBJECTIVE

To determine the population-based prevalence of diabetes and other categories of glucose intolerance (impaired glucose tolerance [IGT] and impaired fasting glucose [IFG]) in Australia and to compare the prevalence with previous Australian data.

RESEARCH DESIGN AND METHODS

A national sample involving 11,247 participants aged > or =25 years living in 42 randomly selected areas from the six states and the Northern Territory were examined in a cross-sectional survey using the 75-g oral glucose tolerance test to assess fasting and 2-h plasma glucose concentrations. The World Health Organization diagnostic criteria were used to determine the prevalence of abnormal glucose tolerance.

RESULTS

The prevalence of diabetes in Australia was 8.0% in men and 6.8% in women, and an additional 17.4% of men and 15.4% of women had IGT or IFG. Even in the youngest age group (25-34 years), 5.7% of subjects had abnormal glucose tolerance. The overall diabetes prevalence in Australia was 7.4%, and an additional 16.4% had IGT or IFG. Diabetes prevalence has more than doubled since 1981, and this is only partially explained by changes in age profile and obesity.

CONCLUSIONS

Australia has a rapidly rising prevalence of diabetes and other categories of abnormal glucose tolerance. The prevalence of abnormal glucose tolerance in Australia is one of the highest yet reported from a developed nation with a predominantly Europid background.

Fetal origins of adult disease?

1. Associations between lower birthweight and higher blood pressure, increased risk of type 2 diabetes and coronary heart disease (CHD) have been observed in a number of different populations worldwide. 2. The reason for this is still debated. Some believe that the observed associations can be explained on the basis of differences in postnatal growth, socioeconomic confounding or genetic factors. Two published studies of birthweight and CHD, with information on later size, suggest that both gestational and postnatal exposures are important. Associations between birthweight and blood pressure, seen in cohorts of twins treated as individuals, have generally remained when data are analysed within twin pairs. Furthermore, similar associations are seen in studies of animals with relative genetic homogeneity kept in standard conditions. These findings suggest that neither socioeconomic nor genetic factors are wholly responsible for the observed associations. 3. If then, there is an underlying causal association, two issues are of fundamental importance. First, is fetal growth (for which birthweight is a summary measure) involved in the causal pathway or is the causal factor a fetal exposure independently associated with fetal growth and increased risk of adult cardiovascular disease? The answer is important in terms of our understanding, the potential for intervention and estimation of the public health implications. Second, are the classic risk factors for CHD in the causal chain between fetal exposures or growth and adult CHD? Most prospective studies measure these factors, but their role as intermediates is unproven. 4. Intervention studies are the best way to test causal hypotheses, but our level of understanding is insufficient to justify such studies in humans, so we rely on animal studies to formally test causal hypotheses. In the present paper, we discuss design and statistical issues in relation to animal studies. The challenge in this field is to devise ways to identify and test potential causal hypotheses in humans.

A prospective study of the association between home gas appliance use during infancy and subsequent dust mite sensitization and lung function in childhood

BACKGROUND

Home gas appliance use has been associated with child respiratory illness but prospective data on the relationship between infant exposure and the development of child allergic disease has not been readily available.

OBJECTIVES

(a) To determine if home gas appliance use is associated with increased risk of house dust mite (HDM) sensitization. (b) To examine whether any association between current home gas use and airway obstruction is influenced by HDM sensitization.

METHODS

DESIGN

an 8-year follow-up birth cohort study of children born during 1988 and 1989.

PARTICIPANTS

a population-based sample (n = 498) of children who participated in the Tasmanian Infant Health Survey (TIHS) and resided in Northern Tasmania in 1997 (84% of eligible children).

MAIN OUTCOME MEASURES

(a) Skin prick test reaction to nine allergens, including Dermatophagoides pteronyssinus (Der p 1) and Dermatophagoides farinae (Der f 1). (b) Spirometric lung function indices, including forced expiratory volume in one second (FEV(1)) and forced vital capacity (FVC).

RESULTS

The relative risk for home gas appliance use at 1 month of age and HDM sensitization was 1.98 (1.04, 3.79) in a cohort analysis with confounder matching. Current home gas use was also associated with HDM sensitization (ARR 1.73 (1.43, 2.76)). Current home gas use was related to a stronger (P = 0.006) reduction in the FEV(1) : FVC ratio among HDM-sensitive children (adjusted difference - 6.2% (- 10.0 to - 2.4)) than non-HDM-sensitive children (adjusted difference - 0.3% (- 2.5 to 1.8)).

CONCLUSION

Indoor pollutants from gas combustion may increase the likelihood of initial sensitization to HDM and play a role in the development of atopic asthma. HDM-sensitized children may be more vulnerable to indoor pollutant-induced airway obstruction. The ability of this study to detect such effects may partly reflect unflued gas appliance use among this sample.

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.

Sources of heterogeneity in the meta-analysis of observational studies: the example of SIDS and sleeping position

The study objective was to provide an example of how risk estimates might vary across studies of observational design, even when a causal association is present and to explore the possible sources of such variation. A meta-analysis of studies on the association between prone sleeping position and sudden infant death syndrome (SIDS) is used to illustrate how risk estimates might vary across studies. Data used were reported case-control studies of the association between sleeping position and SIDS that were published between 1970 and 1994. If the pooled odds ratio had been relied on to assess the association between sleeping position and SIDS without an accompanying examination of the reasons for heterogeneity, important insights into the causal significance of the relationship may have been lost. In meta-analyses of observational studies it is important to investigate the reasons for heterogeneity across studies.

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.

Do larger people have more naevi? Naevus frequency versus naevus density

BACKGROUND

It is unclear which of the number or the density of naevi on the skin is the more appropriate measure of risk of melanoma. Furthermore, the relationship between the number of naevi and their density in an individual has not been explored. Thus, for example, it is unknown if larger people tend to have more naevi by virtue of having a larger skin area, or if the density of naevi is similar in people of different body sizes. In this study, we explored the relationship between the number and the density of naevi in a sample of adolescents.

SUBJECTS AND METHODS

A sample survey of naevi in 472 grade 9 secondary school students (aged 14-15 years) was conducted in Tasmania, Australia during 1992, and a subset of these individuals was followed up in 1997. Counts of naevi of various sizes were taken on the arm, leg, and back. Naevus density was estimated by using an algorithm to estimate body surface area from the height and weight of an individual. More general relationships of the naevus counts to height and weight were also explored. Finally, we considered whether the relationship between naevus density and the anthropometric variables could be confounded by exposure to ultraviolet radiation.

RESULTS

The mean number of naevi was very similar in the two samples. Naevus density was slightly lower in the 1997 sample, mainly because of increasing body size in the cohort. The numbers of naevi were only weakly related to height and weight in males, and there was essentially no relationship in females. Regression analysis showed significant relationships of weight to the back naevus counts in males in 1992 and 1997, and to the arm naevus count in males in 1997; otherwise, none of the regression coefficients for height and weight were statistically significant. This picture did not change following adjustment for potentially confounding variables indicating time spent outdoors or in the sun. Furthermore, there was no evidence that time spent in the sun was related to the body mass index.

CONCLUSIONS

It appears that the number and density of naevi in an individual are unrelated. Accordingly, with the present state of knowledge concerning the risk of melanoma, both the number and density of naevi should be considered as equally valid in future studies as markers of the risk of melanoma, and in studies on the natural history of naevi. If the disease mechanism is systemic, and not related to particular naevi, naevus density might form the better marker of risk. However, if the disease mechanism is related to effects on particular naevi, then the risk would vary in proportion to the number of naevi.

Birth weight, birth length, and bone density in prepubertal children: evidence for an association that may be mediated by genetic factors

There is an incomplete understanding of the contribution of early growth to bone accrual in childhood. The aims of this longitudinal study were to examine the association between growth variables at birth, 1 month, and 8 years and bone density in prepubertal children. Weight and length at both birth and 1 month of age were measured in 1988 as part of a prospective study for sudden infant death syndrome. A total of 330 children (47%) and 278 of their mothers were then contacted in 1996 for measurement of anthropometrics and bone density. Birth weight, birth length, and length gain (but not weight gain) in the first month all made significant contributions to areal bone density (BMD, g/cm(2)) at all sites at age 8 even after taking into account subsequent weight and height gain (model R(2) 14-39% depending on variable and site). Adjustment for potential environmental confounders did not alter these findings, however, adjustment for maternal BMD markedly reduced the early life associations (particularly for birth weight). Though early life factors were weakly associated with bone mineral apparent density (BMAD, g/cm(3)) in correlation analysis, subsequent height and weight gain were the only significant independent contributors to BMAD. In conclusion, early life anthropometrics make little contribution to BMAD (other than through their correlation with later growth) but make significant independent contributions to BMD suggesting that the growth trajectory of bone is determined very early in life. In addition, the contribution of body size at birth to bone growth in early life appears to be mediated by genetic factors although it is possible that it may be mediated by poorly measured or as yet unidentified determinants of body size at birth.