Vastus Lateralis Motor Unit Recruitment Thresholds Are Compressed towards Lower Forces in Older Men.

BACKGROUND: Aging results in adaptations which may affect the control of motor units. OBJECTIVE: We sought to determine if younger and older men recruit motor units at similar force levels. DESIGN: Cross-sectional, between-subjects design. SETTING: Controlled laboratory setting. PARTICIPANTS: Twelve younger (age = 25 ± 3 years) and twelve older (age = 75 ± 8 years) men. MEASUREMENTS: Participants performed isometric contractions of the dominant knee extensors at a force level corresponding to 50% maximal voluntary contraction (MVC). Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis. A surface EMG signal decomposition algorithm was used to quantify the recruitment threshold of each motor unit, which was defined as the force level corresponding to the first firing. Recruitment thresholds were expressed in both relative (% MVC) and absolute (N) terms. To further understand age-related differences in motor unit control, we examined the mean firing rate versus recruitment threshold relationship at steady force. RESULTS: MVC force was greater in younger men (p = 0.010, d = 1.15). Older men had lower median recruitment thresholds in both absolute (p = 0.005, d = 1.29) and relative (p = 0.001, d = 1.53) terms. The absolute recruitment threshold range was larger for younger men (p = 0.020; d = 1.02), though a smaller difference was noted in relative terms (p = 0.235, d = 0.50). These findings were complimented by a generally flatter slope (p = 0.070; d = 0.78) and lower y-intercept (p = 0.009; d = 1.17) of the mean firing rate versus recruitment threshold relationship in older men. CONCLUSION: Older men tend to recruit more motor units at lower force levels. We speculate that recruitment threshold compression may be a neural adaptation serving to compensate for lower motor unit firing rates and/or denervation and subsequent re-innervation in aged muscle.

Health beliefs and Pap smears among Thai women in Brisbane, Australia.

Although a number of studies have assessed the use of Pap smear among Thai women in Thailand, little is known about factors influencing the use of this cervical cancer screening among potentially high risk Thai migrant women. We related health belief model (HBM) factors and sociodemographic variables to the use of Pap smears among migrant Thai women in Brisbane, Australia. A cross-sectional study was conducted in Brisbane, Queensland, Australia. A snowball sampling method was used to recruit 145 women. Thirty-nine percent reported regular Pap smears. Summary HBM index and self-efficacy index were positively associated with Pap smears. Barriers to screening were negatively associated. The HBM appears to be a useful framework for planning cervical cancer prevention. Strategies that reduce barriers to the screening and increase the confidence of women and their self-efficacy are likely to increase their participation.

Why do mothers still sun their infants?

OBJECTIVE: To determine the prevalence of maternal beliefs about the therapeutic uses of sunlight in infancy in tropical Australia. METHODOLOGY: Data were collected by interviewing 114 post-partum patients in Townsville (19 degrees 16'S), Queensland. Each woman was asked a series of open-ended and set-response questions about ancestry, pigmentation, residential history, parity, maternal and paternal education, and beliefs regarding the reputed therapeutic uses of sunlight. RESULTS: Half of the women had at least one risky belief about the perceived benefits of sunning their baby. Thirty-six per cent were in favour of using sunlight to treat neonatal jaundice; 20.2% believed it was necessary to intentionally sun their baby to prevent vitamin D deficiency; and 10.5% thought sunlight was a good remedy for nappy rash. Independent predictors of one or more of these beliefs included maternal age and education level, and having another child that had been treated for jaundice. Forty per cent of multiparous women had sunned a child to treat neonatal jaundice. In most cases, advice to mothers to sun their baby had been given by a midwife/nurse (41% or a doctor/paediatrician (28%). CONCLUSIONS: Post-parturient women had a high prevalence of beliefs that may result in their infant being intentionally exposed to sunlight, and which could increase their child's future risk of skin neoplasia. Midwives and doctors, including paediatricians, were identified as the major professional sources of these beliefs. Professional education is needed to change the beliefs of health professionals who recommend therapies involving sunlight.

Body-site distribution of melanocytic nevi in young Australian children.

OBJECTIVE: To investigate the body-site distribution of melanocytic nevi (MN) with respect to habitually and intermittently sun-exposed surfaces. DESIGN: Cross-sectional survey of MN prevalence. SETTING: Townsville (19.16 degrees S), Queensland, Australia. PARTICIPANTS: Random sample of 506 1- to 6-year-old white children who were born and raised in Townsville (response, 87.6%). MAIN OUTCOME MEASURES: Site-specific counts and densities (number per square meter) of MN. RESULTS: Densities of MN of all sizes were highest on the outer forearms, followed by the outer upper arms, neck, and face. The feet had the lowest density of MN. Densities of MN of 2 mm or greater were highest on the upper arms and trunk. Boys had higher densities of MN of all sizes on the neck than girls (P = .002). Girls had higher densities of MN of 2 mm or greater on the lower legs (P = .006) and thighs (P = .005) than boys. Habitually sun-exposed body sites had higher densities, particularly of small MN, than relatively sun-protected sites, and larger MN were most prevalent on the intermittently exposed skin of the trunk. CONCLUSIONS: These children have higher total body and site-specific MN counts and densities than children from elsewhere, and their MN are distributed over the body in a way that implicates exposure to sunlight. As sun exposure in childhood and MN are risk factors for melanoma, intervention studies are required to determine if MN can be prevented.

Solar UVR exposures of primary school children at three locations in Queensland.

The ultraviolet radiation (UVR) exposures of primary school children in Brisbane, Toowoomba and Mackay (latitudes 27 degrees 30', 27 degrees 33' and 21 degrees 15' south, respectively) were assessed over a period of 2 weeks at each location using UVR-sensitive polysulfone (PS) film badges attached at the shoulder. The students filled in questionnaires on their time spent outdoors for each day of the study. These data in conjunction with the ambient UVR measured by a detector/datalogger unit at each site were used to correlate the calculated exposures with those measured using the PS badges. Overall, the questionnaires indicated that the males spent more time outdoors and had higher measured UVR exposures than females. For both boys and girls at each location, there was a strong correlation between the mean measured UVR exposure and the ambient solar UVR at that location.

Segregation analysis of cutaneous melanoma in Queensland.

To investigate whether the familial clustering of cutaneous melanoma is consistent with Mendelian inheritance of a major autosomal gene, maximum likelihood segregation analyses were performed in a population-based sample of 1,912 families ascertained through a proband with melanoma diagnosed in Queensland between 1982 and 1990. Analyses were performed with the S.A.G.E. statistical package, using the REGTL program for a binary trait with a variable age of onset. We sought medical confirmation for all family members reported to have had melanoma, and only medically verified cases among relatives were included in the analyses. The hypothesis of codominant Mendelian inheritance gave a significantly better fit to the data than either dominant or recessive Mendelian inheritance, or environmental transmission. Overall, both Mendelian inheritance of a single major gene, and purely environmental transmission were rejected (P < 0.001). In both the single major gene and environmental models, there was strong evidence of familial dependence in melanoma occurrence (P < 0.001). These results are consistent with reported genetic heterogeneity in melanoma inheritance and suggest that other familial factors, such as pigmentation, skin type, and sun exposure habits, may play an important role in the familial clustering of melanoma.

Body site specific incidence of basal and squamous cell carcinoma in an exposed population, Townsville, Australia.

Most data on body site distribution of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) do not take into account the surface proportion occupied by body sites experiencing differing amounts of ultraviolet radiation. The recording of BCC and SCC is heterogenous and body sites are not standardized. This study was undertaken to assess the magnitude of the incidence rates of skin cancers at different body sites in a population which experiences high ultraviolet exposure and involved all primary care services in Townsville over 6 weeks in June 1993. The annual site-specific age-standardized (World Population) incidence rates of histologically diagnosed lesions, determined from data where lesions were recorded on a body map, were adjusted for surface area and expressed per 100,000 body units (BU). Relative site densities of lesions were also calculated. Annual incidence rates for BCC per 100,000 BU on the most exposed face (ears, nose and cheeks) were 25,893 (95% confidence interval (c.i.) 18,837-32,950), 13,222 (95% c.i., 8273-18,171) on the less exposed face (forehead,eyebrow, chin and jaw) and 27,837 (95% c.i., 12,560-43,115) on the least exposed face (area within the orbit and nasolabial fold). Incidence rates for SCC rates were highest on the less exposed face, 5843 (95% c.i., 2627-9058) most exposed face, 4200 (95% c.i., 1274-7126) and the exposed upper limb, 3786 (95% c.i., 2783-4789). The relative site density of histologically confirmed BCC was 14 on the most exposed face in males compared with 5 in females and 11 around the eyes (least exposed) in males and 9 in females compared with the body as a whole. Adjustment for body surface proportion demonstrates that highly exposed body sites are at very high risk. The magnitude of the incidence rates on these sites is attributed to the combination of a susceptible population and high ambient ultraviolet radiation (UVR).

MN blood group affects response of serum LDL cholesterol level to a low fat diet.

Previous studies found that MZ twin pairs who are blood group NN have greater intrapair variability in plasma lipid levels than those who are MM or MN. This led to the prediction that the response of plasma lipid levels to a low fat diet would depend on MN blood group, the greatest response being in those who are NN. The present study was based upon 254 patients who took part in the Australian Polyp Prevention Project. This was a 2 x 2 x 2 randomised factorial design based upon the presence or absence of the three factors: a dietary fibre supplement, a beta-carotene supplement and reduced intake of dietary fat. The lowering of plasma, low density lipoprotein (LDL) cholesterol, in response to a low fat diet was greatest in those who were NN and least in MN heterozygotes. Overall, a reduction in LDL level was observed in the 47% of the APPP population who were on a low fat diet and who were homozygous MM or NN. The result was consistent with a balanced polymorphism at or near the GLYA locus on chromosome 4 that influences the sensitivity of plasma lipid levels to dietary fluctuations in fat intake.

Diet and colorectal cancer.

Studies of migrants to Australia indicate that the risk of colorectal cancer (CRC) can be influenced by environment during adult life. Under a gene x environment interaction model for the risk of CRC, it is postulated that a high proportion of the variation in CRC incidence among populations is attributable to differences in diet, and that the average genetic susceptibility of populations to dietary carcinogenic components is similar. The possible relevance within populations of individual susceptibility to dietary components is supported by studies showing that the risk of CRC, compared with that of the general population, is not increased in the spouses of cases. It is postulated that, conditional upon a relevant dietary exposure, the level of susceptibility to diet is a major determinant of variation in individual risk. Despite high correlations of meat and fat with CRC among populations, the results of case-control studies have been inconsistent. Inability to stratify subjects by susceptibility may explain the lack of association of intake of fat and meat with CRC in many studies. A new generation of case-control and cohort studies of diet and CRC may extend the limits of epidemiology. Prevention trials with beta-carotene and other compounds have not protected against colorectal neoplasia, and may have exerted adverse effects. This possibility challenges the philosophy of chemoprevention trials in favor of trials of changes in diet towards patterns that are associated with lower risk.

Accuracy of case-reported family history of melanoma in Queensland, Australia.

A positive family history is used in clinical practice as an indication of increased melanoma risk, yet there are no data on the accuracy of reported family histories of melanoma. The validity of case-reported family history of melanoma was assessed in the course of a family and twin study of melanoma in Queensland, Australia, conducted among the families of 2,118 melanoma cases diagnosed in Queensland between 1982 and 1990. A total of 913 melanoma cases made 1,267 reports of melanoma among their first-degree relatives. A total of 1,040 of these reports were checked, first through relatives themselves and then, if the relative also said they had had melanoma, through the relative's medical records. Medical confirmation of melanoma as the diagnosis was obtained for 623 reports (59.9%; 95% confidence interval 56.9-62.9): a false-positive reporting rate by cases of 40.1%. The level of false-positive reporting was lower for cases under 70 years of age, for women, for cases whose own diagnosis of melanoma was more than 5 years earlier, and for cases with three or more relatives with melanoma. Media campaigns in Queensland aimed at increasing skin cancer awareness, and confusion between melanoma and other more common actinic neoplasma (basal and squamous cell carcinomas), may partly explain the high false-positive reporting rate observed here. For this reason, It is difficult to generalize these findings to northern hemisphere populations where skin cancer is not such an important public health issue.

Risk of colorectal adenomas in patients with a family history of colorectal cancer: some implications for screening programmes.

BACKGROUND AND AIMS: Most colorectal cancers (CRC) arise in colorectal adenomas. A case-control study was conducted to see whether a family history of CRC is associated with a higher prevalence of colorectal adenomas. SUBJECTS: Subjects were drawn from all patients who underwent colonoscopy at the Royal Brisbane Hospital between 1980-1982 and 1985, and included 141 cases with colorectal adenomas diagnosed at colonoscopy and 882 controls who were free of polyps at colonoscopy. METHODS: The prevalence of family history of CRC was compared between patients with adenomas and negative colonoscopy controls. RESULTS: Overall, patients with one first degree relative with CRC were at no greater risk for adenomas at colonoscopy than patients with no family history (odds ratio (OR) = 0.8, 95% confidence intervals (CI) = 0.4, 1.5). Patients with two or more affected first degree relatives had a more than doubled risk for adenomas (OR = 2.3, 95% CI = 0.5, 8.2), and were also more likely to carry moderately or severely dysplastic adenomas (OR = 14.1, 95% CI = 2.0, 62.9). CONCLUSIONS: These findings are consistent with the hypothesis that some families, in addition to those with familial adenomatous polyposis, have an increased susceptibility to develop colorectal adenomas, and that adenomas in such families may have a greater tendency to undergo malignant transformation.

The Queensland Familial Melanoma Project: study design and characteristics of participants.

Family history of melanoma is associated with an increased risk for the disease. Neither the relative contributions of genetic and shared environmental factors to familial risk nor how genetic susceptibility is mediated are known. The Queensland Familial Melanoma Project was undertaken to investigate (a) the role of genetic susceptibility as indicated by skin type, pigmentation and the prevalence of naevi and (b) exposure to solar ultraviolet radiation, and their interaction in the aetiology of familial melanoma. After obtaining doctor's consent, a brief family history questionnaire was mailed to all Queensland residents with a first primary cutaneous melanoma diagnosed between 1982 and 1990. Detailed information on melanoma history and standard melanoma risk factors was sought from all responding twins and familial cases, from a sample of non-familial cases and from cases' relatives. Medical confirmation was sought for all relatives reported to have had melanoma. The final sample comprises 15,907 persons in the 1,912 families of 2,118 melanoma cases, including 509 families in which there are two or more individuals with confirmed melanoma. Melanoma history and risk factors were obtained for 9,746 relatives, including 94 twins of cases. This is the largest family and twin study of cutaneous melanoma yet conducted in an unselected, geographically-defined population. We describe the design of the study and the characteristics of the total study population.

Randomized trial of intake of fat, fiber, and beta carotene to prevent colorectal adenomas.

BACKGROUND: Epidemiologic evidence of associations between the high intake of fat and low intake of dietary fiber, beta carotene, and other dietary constituents and the risk of colorectal neoplasia has been inconsistent and has not provided a sufficient basis for recommendations concerning the dietary prevention of large-bowel cancer in humans. PURPOSE: We conducted a clinical trial to assess the effects on the incidence of adenomas of reducing dietary fat to 25% of total calories and supplementing the diet with 25 g of wheat bran daily and a capsule of beta carotene (20 mg daily). METHODS: We performed a randomized, partially double-blinded, placebo-controlled factorial trial in which half the patients were assigned to each intervention, resulting in seven intervention groups and one control group. Eligibility criteria included histologic confirmation of at least one colorectal adenoma and confidence expressed by the colonoscopist that all polyps had been removed. Dietary changes were individually initiated and monitored by dietitians and research nurses. At surveillance colonoscopy, the size and location of all polyps were recorded, and their histology was later centrally reviewed. Among 424 patients who were randomly assigned in the trial, 13 were found to be ineligible upon histologic review. Among the remaining 411, complete outcome data were collected from 390 at 24 months and from 306 at 48 months. All P values are from two-sided tests of statistical significance. RESULTS: There was no statistically significant prevention of total new adenomas with any of the interventions. We found a statistically non-significant reduced risk of large adenomas (> or = 10 mm) with the low-fat intervention: At 24 months, the odds ratio (OR) adjusted for potential confounders = 0.4 and 95% confidence interval (CI) = 0.1-1.1; at 48 months, OR = 0.3 and 95% CI = 0.1-1.0. Less and statistically nonsignificant reductions in the risk of large adenomas were found with wheat bran: At 24 months, OR = 0.8 and 95% CI = 0.3-2.2; at 48 months, OR = 0.8 and 95% CI = 0.3-2.5. Patients on the combined intervention of low fat and added wheat bran had zero large adenomas at both 24 and 48 months, a statistically significant finding (P = .03). CONCLUSIONS: Because only small numbers of patients were studied, our finding that the combination of fat reduction and a supplement of wheat bran reduced the incidence of large adenomas in this randomized, controlled trial must be treated with caution. The results do suggest, however, that these interventions may reduce the transition from smaller to larger adenomas, a step that may critically define those adenomas most likely to progress to malignancy.

The eastern Australian childhood nevus study: prevalence of atypical nevi, congenital nevus-like nevi, and other pigmented lesions.

BACKGROUND: Various melanocytic lesions are frequently observed. An understanding of phenotypic factors and environmental stimuli that are associated with these lesions may help explain their pathogenesis. OBJECTIVE: This study was undertaken to determine the prevalence of atypical nevi, blue nevi, cafe-au-lait macules, congenital nevus-like nevi, halo nevi, nevi spili, nevi 5 mm or more in diameter, and skin-colored melanocytic nevi in a population of schoolchildren and to explore risk factors including solar radiation in the development of these melanocytic lesions. METHODS: A cross-sectional study was performed by the same medical investigators to examine schoolchildren in three Australian cities that span a wide range of latitudes. RESULTS: Data from 1123 white Australian schoolchildren, 6 to 15 years of age, were analyzed. Acquired melanocytic nevi (atypical nevi, nevi > or = 5 mm in diameter, and skin-colored nevi) were more likely to develop in older fair-skinned subjects who had freckles and lived closest to the equator. Café-au-lait macules and congenital nevus-like nevi were observed in 36.3% and 4.4% of the total population, respectively. Prevalence for both these types of melanocytic lesions increased significantly with decreasing latitude. Halo nevi were present in 5.3% of the subjects and were usually solitary. These lesions were related to the presence of atypical nevi primarily by virtue of their size rather than of other features of clinical atypia. CONCLUSION: Like melanocytic nevi in general, large and atypical nevi are strongly influenced by geographic location and, by implication, degree of solar radiation. The same can be said for congenital nevus-like nevi, which suggests that many so-called congenital nevi are in fact acquired early in life.

How accurate is self-reported family history of colorectal cancer?

Much of the evidence that supports a relation between a positive family history of and increased risk for colorectal cancer is based on information obtained exclusively from patients. There have been few assessments of the accuracy of such data. The validity of self-reported family history of colorectal cancer was assessed in the course of a case-control study of colorectal adenomas conducted among patients aged 20-75 years who underwent colonoscopy in Brisbane, Australia between 1980 and 1985. Family histories reported by a subsample of 237 colonoscopy patients (74 cases and 163 controls) were compared with relatives' medical records and death certificates. Patients' reports of colorectal cancer in 90 relatives were confirmed for 70 (77.8%; 95% confidence interval (CI) 67.8-85.9). Among 124 reports by patients of relatives who had other abdominal cancer or bowel conditions, 114 (91.9%; 95% CI 85.7-96.1) were confirmed to be correct, while 10 (8.1%) were found to be colorectal cancer. Finally, 105 (99.1%; 95% CI 94.9-100.0) of a random sample of 106 completely negative reports by patients were confirmed to be correct. Overall, 77% of positive family histories (any positive relatives) were confirmed, and it was estimated that 98% of negative family histories (no positive relatives) were correct. Cases were slightly more accurate than controls in reporting both positive and negative histories among their relatives. By extrapolation of these results to the total sample of 1,244 patients in the larger case-control study, sensitivity of self-reported positive family history was estimated to be 0.87 among cases and 0.82 among controls, and specificity was estimated to be 0.97 in both groups.

Sun exposure and melanocytic naevi in young Australian children.

Queensland, Australia, has the highest rates of melanoma in the world and Queensland children have the greatest numbers of melanocytic naevi, the strongest risk factor for melanoma. Although both melanoma and naevi are broadly related to sun exposure in childhood, the relation to individual exposure early in life is difficult to study retrospectively in adults. We surveyed 506 children aged 1-6 years who had been born in Townsville, North Queensland. Sun exposure was assessed by questionnaire and melanocytic naevi were counted using a standard international protocol. Very high counts (upper quarter) of melanocytic naevi were significantly associated with sun exposure of more than 4 hours per day (adjusted relative risk ratio 3.29; 95% Cl 1.12-9.69), and with a history of sunburn (1.89; 1.11-3.21). Melanocytic naevus counts increased with age, light skin reflectance, and freckling. With exposure to intense ultraviolet light in Townsville, children develop melanocytic naevi early in life and in large numbers. We found that both acute and chronic exposure to sun are associated with their development.

Changes in serum carotenoids in subjects with colorectal adenomas after 24 mo of beta-carotene supplementation. Australian Polyp Prevention Project Investigators.

The effect of beta-carotene supplementation on major serum carotenoid fractions (lutein/zeaxanthin, beta-cryptoxanthin, lycopene, alpha-carotene, and beta-carotene) was investigated in 224 people with colorectal adenomas (139 men, 85 women) recruited for the Australian Polyp Prevention Project (APPP). Each subject was randomly assigned to take either 20 mg beta-carotene/d or placebo over 24 mo. Besides the expected increase in serum concentration of beta-carotene (1073% in men, 839% in women), lycopene (176% in men) and alpha-carotene (211% in men and 166% in women) concentrations were also increased after body mass index, baseline concentration, change in respective carotenoid intake, and other confounding factors were adjusted for. The increase in serum concentrations of these carotenoids after beta-carotene supplementation suggests that beta-carotene may interact biologically with other carotenoids and such interaction would need to be taken into consideration when the protective effect of beta-carotene supplementation for cancer or other diseases is examined.

Heterogeneity of melanoma risk in families of melanoma patients.

While it is recognized that relatives of melanoma patients are at increased risk for this disease, the source and extent of variation in melanoma risk between families of melanoma cases is unknown. Heterogeneity of familial melanoma risk was assessed among the families (comprising 7,666 first-degree relatives) of 1,149 cutaneous melanoma cases diagnosed in Queensland, Australia, between 1982 and 1987. The measure of familial melanoma risk was based on the number of cases of melanoma in the family in excess of those predicted from the age-, sex-, and birth cohort-specific cumulative incidences of melanoma among all relatives in the sample. Probands over-reported melanoma occurrence among their relatives, with a false positive reporting rate of 44.5% (216 false reports out of 485). Only medically verified cases among relatives were included in the analysis. There was statistically significant heterogeneity in family risk, with 53 (4.7%) of the total 1,116 unrelated families containing significantly more melanoma cases than expected considering the size of the family, and the age, sex, and birth cohort distributions of family members. In univariate analyses, members of the high-risk families were significantly more likely to have poor ability to tan, a propensity to sunburn, fair skin color, red hair, and many melanocytic nevi. When all variables were included simultaneously in a multiple logistic regression model, only the associations with tanning ability, skin color, and number of nevi remained significant. There were no significant differences overall between high-risk and other families in the sites and ages at diagnosis of melanoma, although melanomas on variably sun-exposed sites (trunk and legs) were diagnosed earlier in the high-risk families, independent of the stage at diagnosis.