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T Dwyer

Publications and source records attributed to T Dwyer.

At least 37 records · Page 2Linked to original sources
PubMed2001

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.

Animals↗
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

Breastfeeding in early life and bone mass in prepubertal children: a longitudinal study.

The aim of this study was to determine whether breastfeeding in early life is associated with bone mass in prepubertal children. We studied 330 8-year-old male and female children from Southern Tasmania representing 47% of those who originally took part in a birth cohort study of risk factors for Sudden Infant Death Syndrome in 1988. Breastfeeding intention and habit were assessed in both 1988 and 1996. Bone mineral density was measured by dual-energy X-ray densitometry. Children who were breastfed had higher bone mineral density at the femoral neck (+0.20 SD, p = 0.07), lumbar spine (+0.25 SD, p = 0.03) and total body (+0.29 SD, p = 0.006) compared with those who were bottle-fed. This association with breastfeeding was present in children born at term (femoral neck: +0.26 SD, p = 0.05; lumbar spine: +0.34 SD, p = 0.007; total body: +0.41 SD, p = 0.0008) but not those born preterm, and remained significant after adjustment for size, lifestyle factors and socioeconomic factors. Breastfeeding for less than 3 months was not associated with increased bone mass at any site. In conclusion, this study has demonstrated a beneficial association between breastfeeding in early life and bone mass in 8-year-old children born at term, particularly those breastfed for 3 months or longer, which appears biological. If this association is confirmed in other populations and persists until the attainment of peak bone mass then the implication would be that osteoporosis prevention programs need to start very early in the life cycle.

Analysis of Variance↗
PubMed2000

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.

Absorptiometry, Photon↗
PubMed2000

Maternal diet during pregnancy is associated with bone mineral density in children: a longitudinal study.

OBJECTIVE: To describe the association between maternal diet during the third trimester of pregnancy and bone mass in 8 y-old male and female children. DESIGN: Longitudinal study. SETTING: Southern Tasmania between 1988 and 1996. SUBJECTS: One-hundred and seventy-three 8-y-old male and female children with adequate maternal dietary information taking part in a study of bone mineralization. RESULTS: After adjustment for confounders, femoral neck bone mineral density (BMD) was positively associated with magnesium and phosphorus density of the maternal diet; lumbar spine BMD was positively associated with magnesium, phosphorus and potassium and negatively associated with fat density while total body BMD was positively associated with magnesium, potassium and protein and negatively associated with fat density (all P<0.05). After further adjustment for other significant dietary factors, the only significant remaining associations observed were for phosphorus and fat at the lumbar spine, although the adjusted goodness of fit of the models improved compared to those including one dietary variable. A child in the 'optimal' levels of dietary exposures had significantly higher adjusted BMD at all sites (femoral neck, +5.5%, lumbar spine, +12%, total body, +6.8%). Calcium intake was not associated with BMD at any site, possibly due to a high average intake. CONCLUSIONS: This study reports a substantial association between in utero diet in a well-nourished population and later bone mass in their children. However, it does not allow identification of the dietary components of greatest importance, indicating that these results should be regarded as hypothesis-generating. Further longitudinal studies in other populations are required to confirm that dietary manipulation during pregnancy has a role to play in the early life prevention of osteoporosis.

Bone Density↗
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

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.

Adolescent↗
PubMed2000

The relation between infant indoor environment and subsequent asthma.

Our aim was to examine the contribution of an infant's indoor environment to childhood asthma using prospective data. We conducted a cross-sectional asthma survey in 1995 on 92% (6,378/6,911) of 7-year-olds in Tasmania, Australia. We linked these data with data collected in 1988 as part of the Tasmanian Infant Health Survey, which was designed to investigate sudden infant death. We were able to match 863 records out of the 1,111 in the 1988 survey and the 6,378 in the 1995 survey. The former group was interviewed at home at 1 month of age. In homes where at least one adult smoked in 1988, reported infant exposure to smoking in the same room in 1988 was associated with increased asthma by 1995 (relative risk = 1.52; 95% confidence interval = 1.01-2.29) after adjustment for confounders. The associations between infant exposure to environmental tobacco smoke and asthma were not consistent, however. Gas heater use in 1988 was associated with asthma (relative risk = 1.92; 95% confidence interval = 1.33-2.76). Markers of aeroallergen exposure at 1 month of age were not materially associated with asthma or wheeze. In some settings, air circulation practice with regard to bedroom door closure appeared important. Poor indoor air quality may play an important role in the development of childhood asthma.

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

Effect of muscle length on strength and dexterity after stroke.

OBJECTIVE: The effect of muscle length on strength and dexterity after stroke was investigated. The aim was to determine if poor function at a particular muscle length could be attributed solely to differential weakness at this joint angle or whether an additional problem of differential dexterity exists. DESIGN: This descriptive research study measured elbow flexor and extensor strength as well as dexterity at three elbow joint angles: 30 degrees , 60 degrees and 90 degrees flexion. Dexterity was measured independently of strength. SUBJECTS: Fifteen (seven female, eight male) chronic stroke patients (mean age 67 years) who could actively flex and extend their affected elbow participated. Ten neurologically normal control subjects (mean age 67 years) acted as controls. MAIN OUTCOME MEASURES: Strength was measured as peak elbow flexor and extensor torque at three angles; and dexterity was measured as coherence for slow and fast tracking also at three angles. RESULTS: Dexterity was not affected by muscle length but strength was and this finding was the same for both stroke and controls. While the magnitude of the torque-angle curves was not significantly different between stroke and controls, the shape of torque-angle curves was altered after stroke so that both the elbow flexors (p < 0.05) and extensors (p < 0.05) tested weaker in the testing position where they were shortest. CONCLUSION: Since there was no differential loss of dexterity, it appears that differential loss of strength, especially in the shortened range, may explain the clinical observation of poorer function at one muscle length than another after stroke. Specific training to strengthen the muscles in these ranges is therefore of clinical importance for rehabilitation.

Aged↗
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↗
PubMed2000

The changing incidence and spectrum of thyroid carcinoma in Tasmania (1978-1998) during a transition from iodine sufficiency to iodine deficiency.

Exposure to ionizing radiation, changing levels of iodine nutrition, and increased pathologic diagnosis of clinically unimportant thyroid neoplasia have all been proposed as explanations for a worldwide rise in the incidence of thyroid carcinoma (TC) over the past 6 decades. Tasmania is geographically an area of endemic iodine deficiency. In this report, we describe the spectrum of TC in a population averaging 450,000 persons during a 21-yr period that spans the communities transition from iodine sufficiency to iodine deficiency after discontinuation of universal iodine prophylaxis in the mid 1980s. The Tasmanian Cancer Register was used to ascertain all cases of TC diagnosed in Tasmania between 1978 and 1998. Histopathological and demographic data were reviewed. A total of 289 cases of TC were identified. Papillary TC (PTC), follicular TC, medullary TC, and other species accounted for 62%, 23%, 4%, and 11% of cases, respectively. The age standardized incidence rate for total TC increased from 2.45 to 5.33 per 100,000 for females and 0.75 to 1.76 per 100,000 for males between 1978 and 1984 and 1992 and 1998, respectively. A rise in the incidence of PTC by 4.5-fold (P < 0.05) in females and 2.1-fold in males (not significant) was the dominant change over this period. In parallel, the proportion of follicular TC relative to PTC fell from 0.35 to 0.17 during these years (P < 0.05). The rise in PTC incidence was, in part, due to an increase in the occurrence of tumors 1cm or less in diameter. Nonetheless, a 3-fold rise in incidence of larger lesions was also observed during the study period. Forty-three (24%) PTC cases had multifocal disease, 17 (40%) of whom had bilateral tumors. Familial (autosomal dominant) PTC was identified in nine (5%) total PTC cases. Prior studies have linked iodine prophylaxis to a rise in the proportion of differentiated TC, particularly PTC. Our data suggest a complex relationship between iodine nutrition and thyroid tumorigenesis. Factors such as a long latency between changes in iodine nutrition and thyroid tumorigenesis, a dose threshold for the effect of iodine nutrition on thyroid tumorigenesis, and an interaction between iodine nutrition and thyroidal sensitivity to ionizing radiation may all play a role.

Adenocarcinoma, Follicular↗
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

Management of insulin-treated diabetes in Tasmania.

OBJECTIVE: To evaluate patterns of self-management, healthcare utilisation and screening for major complications among Tasmanians with insulin-treated diabetes. MAIN OUTCOME MEASURES: Frequency of self-monitoring of blood glucose, health care utilisation and screening for diabetic complications. DESIGN AND SETTING: A questionnaire survey of 1517 people listed on the Tasmanian Diabetes Register in 1995-1997. RESULTS: Response rate was 79.5%. Self-monitoring of blood glucose was reported by 98% of respondents, daily self-monitoring by 74%. About 41% of respondents were being managed jointly by GPs and diabetes specialists, 29% solely by GPs and 25% solely by diabetes specialists. Over 96% visited the doctor treating their diabetes more than once a year, but 21% reported they had never visited a diabetes educator and 43% reported they had never visited a dietitian. Most respondents aged > or = 25 years (90%) reported having an eye examination within the past two years, almost all by an eye specialist. Blood pressure was commonly assessed, but most adults indicated that the doctor treating their diabetes did not routinely examine their feet. Nearly 19% of respondents smoked cigarettes. CONCLUSIONS: Some aspects of diabetes self-care and medical care have improved in Tasmania since the 1984 survey (eg, frequency of self-monitoring of blood glucose rose from 50% to 98%). However, our findings suggest that further improvements are needed to increase daily self-monitoring of blood glucose, attendance at diabetes educator and dietitian services, and foot examinations by doctors. Additional efforts are also needed to lower the prevalence of smoking.

Adolescent↗
PubMed1999

Tobacco smoke exposure at one month of age and subsequent risk of SIDS--a prospective study.

The aim of this investigation was to identify the sources of postnatal exposure to tobacco smoke at 1 month of age and to examine their relation to sudden infant death syndrome (SIDS). The Tasmanian Infant Health Survey was a prospective cohort study undertaken from 1988 to 1995. It involved 9,826 infants (89% of eligible infants) at higher risk of SIDS. Subsequently 53 eligible infants died of SIDS. Hospital interviews were available on 51 and home interviews on 35 SIDS infants. Urinary cotinine assays were conducted using gas-liquid chromatography (n = 100). Within a predictive model that explained 63% of urinary cotinine variance, the strongest predictor of cotinine and also of SIDS was maternal smoking, though the effects of prenatal and postnatal smoking could not be separated. However, for particular smoking-related behaviors, there was a discordance between prediction of cotinine concentration and prediction of risk of SIDS. If smoking mothers did not smoke in the room with the baby, the cotinine level in the infant's urine was reduced by a little more than a half (p = 0.009), but this was not associated with a reduction in SIDS risk (odds ratio = 1.09, 95% confidence interval 0.47-2.55). Similarly, the presence of other adult resident smokers was associated with a 63% increase in urinary cotinine (p = 0.047) but not with increased SIDS risk (odds ratio = 0.69, 95% confidence interval 0.34-1.40). However, the study lacked the power to detect modest effects, that is, those altering risk less than twofold.

Adult↗