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Biomedical subjects

B Rockhill

Publications and source records attributed to B Rockhill.

13 recordsLinked to original sources
PubMed1998

Physical activity and breast cancer risk in a cohort of young women.

BACKGROUND: Increased physical activity has been hypothesized to be a means of breast cancer prevention. We examined the associations between physical activity at two different times in life and breast cancer risk. METHODS: We analyzed data from the Nurses' Health Study II, a prospective study of women aged 25-42 years in 1989. On the baseline survey, women were asked, "While in high school and between the ages 18 and 22 years, how often did you participate in strenuous physical activity at least twice a week?" We averaged answers to these two questions to develop a measure of late adolescent activity. Women were also asked at baseline to report the number of hours per week they currently spent in different nonoccupational activities. During 6 years of follow-up, we identified 372 cases of invasive breast cancer. Data were analyzed by use of multivariate pooled logistic regression to produce relative risk (RR) and confidence intervals (CIs) of being diagnosed with the disease. RESULTS: Women who were more active in late adolescence were not at reduced risk of breast cancer compared with less active women. For those women who reported engaging in strenuous activity at least twice per week for 10-12 months per year in late adolescence, the RR of cancer, compared with those who never engaged in such activity, was 1.1 (95% CI = 0.8-1.6). Similarly, higher levels of recent nonoccupational physical activity were not associated with reduced risk of breast cancer (RR for > or = 7 hours of activity/week relative to < 1 hour/week = 1.1; 95% CI = 0.8-1.5). CONCLUSION: Our findings do not support a link between physical activity, in late adolescence or in the recent past, and breast cancer risk among young adult women.

Adolescent↗
PubMed1998

Population attributable fraction estimation for established breast cancer risk factors: considering the issues of high prevalence and unmodifiability.

Established breast cancer risk factors, in addition to being relatively unmodifiable, are highly prevalent among US women. Previous reports of population attributable fraction for the established risk factors have used definitions that resulted in 75-100% of women in the source population labeled exposed. The practical value of such estimates has not been discussed; further, the estimates have frequently been misinterpreted. In the context of examining the interpretation and public health value of such estimates, the authors demonstrate the sensitivity of the population attributable fraction to changes in exposure cutpoints. They use data from the Carolina Breast Cancer Study, a case-control study of breast cancer conducted in North Carolina between 1993 and 1996. For the four established risk factors (menarche before age 14 years, first birth at age 20 years or later/nulliparity, family history of breast cancer, and history of benign breast biopsy), the estimated population attributable fraction was 0.25 (95% confidence interval 0.06-0.48). Over 98% of the source population was exposed to at least one of these risk factors. The population attributable fraction estimate was reduced to 0.15 when more restrictive definitions of early menarche (less than age 12 years) and late age at first full-term pregnancy (30 years or more) were used (proportion exposed, 0.62). Population attributable fractions for established breast cancer risk factors probably have little public health value because of both the high proportions exposed and the relative unmodifiability of the risk factor distributions.

Adolescent↗
PubMed1998

Cigarette smoking, N-acetyltransferases 1 and 2, and breast cancer risk.

To examine the effects of smoking and N-acetylation genetics on breast cancer risk, we analyzed data from an ongoing, population-based, case-control study of invasive breast cancer in North Carolina. The study population consisted of 498 cases and 473 controls, with approximately equal numbers of African-American and white women, and women under the age of 50 and age 50 years or older. Among premenopausal women, there was no association between current smoking [odds ratio (OR), 0.9; 95% confidence interval (CI), 0.5-1.5] or past smoking (OR, 1.0; 95% CI, 0.6-1.6) and breast cancer risk. Among postmenopausal women, there was also no association with current smoking (OR, 1.2; 95% CI, 0.7-2.0); however, a small increase in risk was observed for past smoking (OR, 1.5; 95% CI, 1.0-2.4). For postmenopausal women who smoked in the past, ORs and 95% CIs were 3.4 (1.4-8.1) for smoking within the past 3 years, 3.0 (1.3-6.7) for smoking 4-9 years ago, and 0.6 (0.3-1.4) for smoking 10-19 years ago. Neither N-acetyltransferase 1 (NAT1) nor N-acetyltransferase 2 (NAT2) genotype alone was associated with increased breast cancer risk. There was little evidence for modification of smoking effects according to genotype, except among postmenopausal women. Among postmenopausal women, ORs for smoking within the past 3 years were greater for women with the NAT1*10 genotype (OR, 9.0; 95% CI, 1.9-41.8) than NAT1-non*10 (OR, 2.5; 95% CI, 0.9-7.2) and greater for NAT2-rapid genotype (OR, 7.4; 95% CI, 1.6-32.6) than NAT2-slow (OR, 2.8; 95% CI, 0.4-8.0). Future studies of NAT genotypes and breast cancer should investigate the effects of environmental tobacco smoke, diet, and other exposures.

Acetyltransferases↗
PubMed1997

Validity and efficiency of approximation methods for tied survival times in Cox regression.

Survival-time studies sometimes do not yield distinct failure times. Several methods have been proposed to handle the resulting ties. The goal of this paper is to compare these methods. Simulations were conducted, in which failure times were generated for a two-sample problem with an exponential hazard, a constant hazard ratio, and no censoring. Failure times were grouped to produce heavy, moderate, and light ties, corresponding to a mean of 10.0, 5.0, and 2.5 failures per interval. Cox proportional hazards models were fit using each of three approximations for handling ties with each interval size for sample sizes of n = 25, 50, 250, and 500 in each group. The Breslow (1974, Biometrics 30, 89-99) approximation tends to underestimate the true beta, while the Kalbfleisch-Prentice (1973, Biometrika 60, 267-279) approximation tends to overestimate beta. As the ties become heavier, the bias of these approximations increases. The Efron (1977, Journal of the American Statistical Association 72, 557-565) approximation performs far better than the other two, particularly with moderate or heavy ties; even with n = 25 in each group, the bias is under 2%, and for sample sizes larger than 50 per group, it is less than 1%. Except for the heaviest ties in the smallest sample, confidence interval coverage for all three estimators fell in the range of 94-96%. However, the tail probabilities were asymmetric with the Breslow and Kalbfleisch-Prentice formulas; using the Efron approximation, they were closer to the nominal 2.5%. Although the Breslow approximation is the default in many standard software packages, the Efron method for handling ties is to be preferred, particularly when the sample size is small either from the outset or due to heavy censoring.

Bias↗
PubMed1993

Health-related risk factors in a sample of Hispanics and whites matched on sociodemographic characteristics. The Stanford Five-City Project.

Although past studies have compared health-related risk factors in Hispanics and whites, few studies have controlled for potential confounding from sociodemographic variables. Using data on men and women aged 25-74 years who responded to biennial cross-sectional surveys conducted in four diverse California cities from 1979 to 1990, the authors employed a matched-pairs design in which 756 Hispanic respondents were matched to 756 white respondents according to age, sex, educational level, city of residence, and time of survey. No significant differences between Hispanics and whites were found for any of the blood pressure indicators (systolic and diastolic blood pressure, prevalence of hypertension, and use of antihypertensive medication), caloric intake, total cholesterol, alcohol intake, or physical activity. The only variables for which Hispanics had higher levels of risk factors than whites were body mass index (weight (kg)/weight (m)2; 27.5 vs. 25.6, p < 0.001) and high density lipoprotein cholesterol (48.6 mg/dl vs. 50.1 mg/dl, p < 0.03). Whites, on the other hand, were significantly more likely to be current smokers than Hispanics (34.2% vs. 24.0%, p < 0.001) and, among smokers, to smoke a greater number of cigarettes per day (19.7 vs. 11.4 cigarettes/day, p < 0.001). Whites were also significantly more likely to have higher-fat diets, as measured by percentages of calories derived from total fat (37.6% vs. 35.1%, p < 0.04) and saturated fat (13.6% vs. 12.3%, p < 0.03). Examination of interactions indicated further risk factor differences by ethnicity across several sex, age, and educational subgroups.

Adult↗
PubMed1993

Cigarette smoking trends in adolescents and young adults: the Stanford Five-City Project.

BACKGROUND: Data on smoking prevalence from four cross-sectional community-based surveys (1979-1990) are presented for 2,605 adolescents and young adults 12-24 years of age. METHODS: The surveys were conducted in two treatment and two control cities in Northern California as part of the Stanford Five-City Project, a multifactor cardiovascular disease prevention study. RESULTS: Over the 12-year study period, prevalence of daily smoking declined in all cities by approximately 50% among 16- to 19- and 20- to 24-year-olds but showed little change among those 12-15 years old. Although the declines were especially large in the two treatment cities and in one control city, the declines in treatment cities were not significantly different from those in control cities. During each period, smoking prevalence escalated most sharply between the ages of 12-15 and 16-19, the period of development when students advanced from junior high to high school. CONCLUSIONS: Despite impressive secular declines, it appears that the Five-City Project community intervention, which targeted smoking in adults, did not have a diffusion effect on the tobacco use habits of adolescents.

Adolescent↗
PubMed1992

Trends in cardiovascular disease risk factors by educational level: the Stanford Five-City Project.

BACKGROUND: Trends in blood pressure, smoking, and cholesterol were examined from 1979-1980 through 1985-1986 in four cities in California by level of education (< high school, high school graduate, some college, college or postgraduate). METHODS: Four biennial cross-sectional surveys (n = 6,580) were conducted in two treatment and two control cities to evaluate a 6-year community health education intervention, conducted as part of the Stanford Five-City Project. RESULTS: Over the 8-year study period, men and women ages 25-74 from each educational group in the treatment cities showed significant declines in smoking prevalence and levels of blood pressure and cholesterol (with the exception of cholesterol in women). In general, declines in the least educated group (< high school) were stronger than declines in the most educated group (college or postgraduate). Similar declines occurred in each educational group in control cities. CONCLUSIONS: These results illustrate that persons from all educational levels can modify their risk for CVD and are of particular importance because of the higher prevalence of CVD risk factors among those with less education. The similarity of time trends in treatment as well as control cities suggests that the broad-based, multisource health education efforts in the United States are succeeding across the educational spectrum.

Adult↗
PubMed1992

The medical origins of homelessness.

In 1989 through 1990, we conducted a cross-sectional survey of 1437 homeless adults in northern California (98% response rate). Prevalences of alcohol abuse, illegal drug use, and psychiatric hospitalization when adults first became homeless were 15% to 33% lower than prevalences following homelessness. The largest differences between the homeless and a comparison group of 3122 nonhomeless adults were for psychiatric hospitalization (odds ratios [ORs] of 4.6 for men and 5.9 for women) and alcohol abuse (ORs of 2.3 for men and 4.0 for women). However, when prehomeless prevalences of addictive and psychiatric disorders were compared with prevalences among the nonhomeless, absolute differences were no greater than 12%.

Adolescent↗
PubMed1991

Predictors of physician's smoking cessation advice.

OBJECTIVES: To determine the percentage of smokers reporting that a physician had ever advised them to smoke less or to stop smoking, and the effect of time, demographics, medical history, and cigarette dependence on the likelihood that respondents would state that a physician had ever advised them to stop smoking. DESIGN AND SETTING: Data were collected from the Stanford Five-City Project, a communitywide health education intervention program. The two treatment and three control cities were located in northern and central California. As there was no significant difference between treatment and control cities regarding cessation advice, data were pooled for these analyses. PARTICIPANTS: There were five cross-sectional, population-based Five-City Project surveys (conducted in 1979-1980, 1981-1982, 1983-1984, 1985-1986, and 1989-1990); these surveys randomly sampled households and included all residents aged 12 to 74 years. MAIN OUTCOME MEASURES: Improved smoking advice rates over time in all towns was an a priori hypothesis. RESULTS: Of the 2710 current smokers, 48.8% stated that their physicians had ever advised them to smoke less or stop smoking. Respondents were more likely to have been so advised if they smoked more cigarettes per day, were surveyed later in the decade, had more office visits in the last year, or were older. In 1979-1980, 44.1% of smokers stated that they had ever been advised to smoke less or to quit by a physician, vs 49.8% of smokers in 1989-1990 (P less than .07). Only 3.6% of 1672 ex-smokers stated that their physicians had helped them to quit. CONCLUSION: These findings suggest that physicians still need to increase smoking cessation counseling to all patients, particularly adolescents and other young smokers, minorities, and those without cigarette-related disease.

Adolescent↗
PubMedDate not supplied

Improved cholesterol-related knowledge and behavior and plasma cholesterol levels in adults during the 1980s.

OBJECTIVES: To determine whether cholesterol-related knowledge and behavior and plasma cholesterol levels were stable until the inception of large-scale national interventions in the middle to late 1980s, whether they subsequently improved, and whether these levels varied by subgroups. DESIGN, SETTING, AND PARTICIPANTS: Data were collected from 4173 adults aged 25 through 74 years in the two control cities (San Luis Obispo and Modesto, Calif) of the Stanford Five-City Project. Five separate, community-based surveys were conducted in 1979-1980, 1981-1982, 1983-1984, 1985-1986, and 1989-1990. RESULTS: Cholesterol-related knowledge and behavior and plasma cholesterol levels improved (P = .0001) in both cities after the early 1980s. Those who were more educated, female, older, or nonsmokers had significantly higher knowledge and behavior scores, and those who were younger, more educated, or normotensive had significantly lower plasma cholesterol levels. CONCLUSION: Improvements in this population's cholesterol-related knowledge and behavior and plasma cholesterol levels began in 1985-1986, suggesting that the extensive cholesterol interventions that began in the middle 1980s in the United States created positive cholesterol-related changes at the community level.

Adult↗
PubMedDate not supplied

Improvements in cholesterol-related knowledge and behavior and plasma cholesterol levels in youths during the 1980s.

This article examines cholesterol-related knowledge, cholesterol-related behaviors, and plasma cholesterol levels in 12-24-year-olds, using data collected from four community-based cross-sectional surveys conducted 1979-1980, 1981-1982, 1985-1986, and 1989-1990. Participants included 1,552 individuals from randomly sampled households in two control cities (San Luis Obispo and Modesto, California) of the Stanford Five-City Project. Over the eleven-year study period, cholesterol-related knowledge improved in both control cities (P < .0002). Cholesterol-related behavior (P < .0003) and plasma cholesterol levels (P < .002) significantly improved only in San Luis Obispo (a college city with more 19-24-year-olds and a better-educated population than Modesto). In general, knowledge and behavior scores and plasma cholesterol levels were lower in these 12-24-year-olds than in 25-74-year-olds, although trends at all ages were similar over time and by demographic variables. Although the cholesterol-related interventions that began in the mid-1980s primarily targeted adults, these 12-24-year-olds' cholesterol-related knowledge improved (as did, to a lesser extent, their cholesterol-related behavior and plasma cholesterol levels). These findings have implications for upcoming youth-related cholesterol interventions.

Adolescent↗