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Biomedical subjects

C Ritenbaugh

Publications and source records attributed to C Ritenbaugh.

At least 55 records · Page 3Linked to original sources
PubMed1995

A brief, telephone-administered food frequency questionnaire can be useful for surveillance of dietary fat intakes.

A 13-item questionnaire designed for quick telephone administration was evaluated for use in surveillance of fat intake in the United States. Study populations included 560 middle-aged and older adults from Beaver Dam, WI, 252 middle-aged and older women from Wisconsin, 73 young, low income Hispanic women from Chicago, IL, 52 older adults from Arizona and 135 younger adults from Augusta, GA. Correlations between fat scores and fat intakes measured by multiple food records or recalls or by more extensive food frequency questionnaires ranged from 0.33 to 0.60, similar to results from other published questionnaire validation studies. Correlations with percentage of energy from fat were lower (0.26 to 0.42), except for the Chicago population, for which there was no correlation (-0.02). There was no systematic variation in correlations among other subgroups defined by demographic and health-related characteristics, including race (black vs. white). Most, but not all, of the substantial differences in fat intakes among subgroups were identified by the questionnaire. The questionnaire will not capture small differences in intakes among groups and is inappropriate when the sample size is limited or for populations with diets substantially different from the typical U.S. diets, such as the Chicago population. However, with attention to its limitations, the questionnaire is useful for surveillance.

Adolescent↗
PubMed1995

Design and recruitment for retinoid skin cancer prevention (SKICAP) trials. The Southwest Skin Cancer Prevention Study Group.

The retinoid skin cancer prevention (SKICAP) trials are a set of double-blind, randomized, placebo-controlled clinical trials. The SKICAP-actinic keratoses (AK) trial tests the hypothesis that daily supplementation of retinol (25,000 IU) for 5 years reduces the incidence of skin cancers in high-risk individuals, those with a history of greater than ten clinically or pathologically diagnosed AK and, at most, one prior pathologically confirmed cutaneous squamous cell carcinoma (SCC) or basal cell carcinoma (BCC). The SKICAP-SCC/BCC (S/B) trial tests the hypothesis that daily supplementation of retinol (25,000 IU) or 13-cis-retinoic acid (5 or 10 mg) for 3 years reduces skin cancer incidence in very high-risk individuals, those with a history of at least four pathologically confirmed SCCs or BCCs. Between 1984 and 1988, 2800 participants were enrolled at two clinics on the SKICAP-AK trial; and between 1985 and 1990, a total of 719 participants were enrolled at four clinics on the SKICAP-S/B trial. The initial recruitment strategy was referral by dermatologists, but low accrual necessitated the use of other strategies to achieve enrollment goals, which included involving additional clinics and using paid trial-specific advertisements in print and electronic media. Thirteen % of the SKICAP-AK participants and 36% of the SKICAP-S/B participants were enrolled through dermatologist referral, whereas paid advertisements resulted in enrollment of 87% of SKICAP-AK and 43% of SKICAP-S/B participants. A population-based skin cancer registry was used to identify and enroll the remaining 21% of the SKICAP-S/B participants.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Risk factors for Barrett's oesophagus: a life history approach to behavioural assessment in the distant past.

Little is known about the aetiology of Barrett's oesophagus, a condition in which columnar epithelium replaces normal squamous epithelium above the juncture of the oesophagus with the stomach. An exploratory retrospective study of males from the Tucson Veteran's Affairs Medical Center (Tucson, AZ, USA), looking at 22 Barrett's cases and 22 controls, was undertaken to: (1) determine whether risk factors previously reported for squamous oesophageal cancer were also potential risk factors for Barrett's oesophagus; and (2) explore which of several retrospectively determined dietary factors would permit maximum discrimination of Barrett's cases from controls. Because of the recognized difficulty with retrospective dietary assessment, an intensive interview-based life history approach was developed to assess behavioural factors throughout adulthood. We examined the dose-response relationship involving questions (1) and (2) separately for subjects with lesions less than or greater than 7 cm in length. A literature-based oesophageal cancer risk factor score (including use of tobacco and intakes of alcohol, fat, vitamin A, linoleic acid and protein) discriminated cases from controls. Alcohol consumption alone discriminated patients with lesions < 7 cm in length from controls, and a more complex risk factor score (including tobacco use, alcohol, fat, fruits and vegetables) discriminated patients with lesions > 7 cm in length from controls.

Adult↗
PubMed1994

Comparative exposure ratios: a non-parametric, multifactor technique for case-control studies.

The odds ratio in a two-by-two table is widely used in case-control studies to measure association between disease and a binary risk factor. In this article we propose a more general measure of association, the comparative exposure ratio (CER), which is the ratio of the number of case-control pairs where the case has greater exposure divided by the number where the control has greater exposure. In simple cases, the CER is an odds ratio or a weighted combination of odds ratios. In more general cases, a CER continues to measure association even when an odds ratio computation is not feasible. Moreover, CERs improve on odds ratios in several ways: they do not require binary risk factors, or a choice of the scale of measurement of continuous risk factors; they make it possible to investigate multiple risk factors simultaneously, without multivariate parametric assumptions; they also can be used to detect patterns that might indicate possible causal pathways. We illustrate how various choices of the definition of 'greater exposure' make the CER a powerful and flexible tool. We give expressions for confidence intervals for CERs, and verify in a pilot simulation that they are valid. Finally, we illustrate with a case-control study of cervical dysplasia how exploratory inference using CERs can be carried out.

Case-Control Studies↗
PubMed1993

Resistance exercise training is associated with decreases in serum low-density lipoprotein cholesterol levels in premenopausal women.

BACKGROUND: Aerobic exercise training is associated with reduced serum concentrations of triglycerides, increased concentrations of high-density lipoprotein cholesterol, and minimal changes in serum levels of total cholesterol or low-density lipoprotein cholesterol. There are few data on the effects of resistance exercise on blood lipid levels. METHODS: Premenopausal women were randomly assigned to a supervised resistance exercise training program (n = 46) or a control group (n = 42) for 5 months. Serum was analyzed for levels of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglycerides. Body composition and dietary intake were also measured. RESULTS: The exercise group showed a 0.33 +/- 0.03-mmol/L (mean +/- SE) decrease in total cholesterol level and a 0.36 +/- 0.001-mmol/L decrease in low-density lipoprotein cholesterol level that was significantly different from the control group. No significant changes were noted in serum high-density lipoprotein cholesterol or triglyceride levels in either group. Changes in body composition showed no significant correlations with changes in total cholesterol or low-density lipoprotein cholesterol. There were no significant differences in nutrient intake between the groups. CONCLUSION: In healthy, premenopausal women, with normal baseline lipid profiles, 5 months of resistance exercise training was associated with significant decreases in serum total cholesterol and low-density lipoprotein cholesterol concentrations.

Adult↗
PubMed1993

Dietary supplementation: the case for placebo-controlled trials.

There are a variety of ways in which we learn about the relationship of diet to cancer prevention or cancer etiology in humans. Epidemiologic studies provide the basis for many of our hypotheses, while animal studies provide opportunities to try out more specific models. However, only human clinical trials can adequately test these concepts and identify which food compounds are related to cancer prevention. Further, clinical trials can provide opportunities to examine underlying mechanisms. Clinical trials in the area of diet and cancer prevention have largely been of two types: single (or dual) nutrients (purified, in high-dose pills) tested in double-blind placebo-controlled trials, and randomized dietary interventions, using education of the subjects to achieve broad scale dietary change. This paper argues for an intermediate form of clinical trial, using a food-based supplement in a randomized double-blind placebo-controlled design. This model is particularly appropriate for studying food components such as fiber for which the activity may rely on higher order structure.

Clinical Trials as Topic↗
PubMed1993

Evaluation of a brief telephone questionnaire to estimate fruit and vegetable consumption in diverse study populations.

We evaluated the use of a six-item telephone questionnaire to estimate fruit and vegetable intakes in five diverse populations. Researchers administered the telephone questionnaire to persons who had previously undergone more extensive dietary assessment. The study population included 553 middle-aged and older adults in Beaver Dam, WI; 252 middle-aged and older women throughout Wisconsin; 150 parents of school children in Augusta, GA; 73 low-income, Hispanic mothers in Chicago, IL; and 51 older adults in Arizona. Spearman correlation coefficients between total fruit and vegetable intakes measured by the brief telephone survey and by more extensive food frequency questionnaires were 0.47 (Augusta), 0.48 (Arizona), 0.56 (Wisconsin), and 0.57 (Beaver Dam). Correlations between intakes measured by the brief telephone survey and by multiple diet records or recalls were 0.29 (Arizona), 0.46 (Chicago), and 0.54 (Beaver Dam). With the exception of Arizona, mean daily fruit and vegetable intakes measured by the telephone survey were similar to intakes estimated by multiple diet records or recalls and lower than those estimated by extensive food frequency questionnaires. Although caution may be needed in interpreting dietary reports from some ethnic subgroups, this brief telephone questionnaire may be useful for surveillance of fruit and vegetable intake in the United States.

Adolescent↗
PubMed1992

Reduction in plasma or skin alpha-tocopherol concentration with long-term oral administration of beta-carotene in humans and mice.

BACKGROUND: Beta-carotene is one of the most commonly used compounds in clinical trials of chemopreventive agents in various neoplastic diseases. Animal studies, including our own, have documented that dietary beta-carotene can reduce plasma alpha-tocopherol (vitamin E) levels, but few published studies have examined the clinical or pharmacokinetic ramifications of long-term, high-dose beta-carotene regimens on other fat-soluble vitamins such as alpha-tocopherol. PURPOSE: This study was designed to determine the effects of long-term beta-carotene supplementation on plasma concentrations of alpha-tocopherol in normal human subjects and in an experimental C3H/HeN mouse model. METHODS: In a double-blind study, 45 normal subjects were randomly assigned to receive 0 (placebo), 15, 30, 45, or 60 mg of oral beta-carotene daily for approximately 9 months. Monthly plasma samples were collected. Thirty-five C3H/HeN mice were fed a basal diet with or without beta-carotene and treated topically with or without alpha-tocopherol, except for the control mice, which received UV radiation for 27 weeks from week 3 to week 30. Plasma and dorsal skin samples were taken after 40 weeks and were analyzed for alpha-tocopherol and/or beta-carotene by high-performance liquid chromatography. RESULTS: Long-term dietary beta-carotene administration resulted in statistically significant reductions in levels of alpha-tocopherol in the skin and plasma of UV-irradiated mice. In the human study, the decrease in plasma alpha-tocopherol levels was progressive and significant between 6 and 9 months of beta-carotene dosing in all dosage groups. The greatest decrease was observed during the 9th (last) month of dosing, with a decrease of 40% from baseline. All oral beta-carotene doses (15-60 mg/d), however, resulted in similar decreases in steady-state plasma levels of alpha-tocopherol and in only small differences in beta-carotene plasma levels. CONCLUSION: Long-term oral administration of beta-carotene decreased steady-state plasma concentrations of alpha-tocopherol. The lack of a significant dose-response effect between doses of beta-carotene and alpha-tocopherol plasma levels is not unexpected, given the small differences in steady-state beta-carotene plasma levels in the four beta-carotene dose groups. IMPLICATIONS: Studies are needed to determine how long-term beta-carotene dosing influences tissue distribution of dietary alpha-tocopherol. Careful surveillance for this and other potentially harmful nutrient interactions should become part of all long-term intervention studies.

Administration, Oral↗
PubMed1992

The effectiveness of adherence intervention in a colon cancer prevention field trial.

BACKGROUND: Adherence interventions were implemented in a 1-year community-based colon cancer prevention clinical trial (n = 110) using wheat bran fiber and calcium dietary supplements. The adherence promotion strategy was guided by a theoretical model. METHODS: The adherence intervention contains both a generalized portion given to all participants and an individualized portion given to marginal (50-74% intake) and low (under 50% intake) adherers. A regression model was employed to assess the effectiveness of the interventions both at the first intervention and at subsequent times. RESULTS: The Health Behavior in Cancer Prevention Model-based adherence promotion intervention was associated with retention of participants, both during the run-in period and after randomization (P = 0.05); and maximization of the percentage of the 13.5-g recommended fiber supplement consumed during the trial (92.5%). The positive effects of the adherence intervention were greater with first-time nonadherers and the control group than with the experimental group. The high-fiber group had notably more biological GI effects from the increased fiber intake, more preexisting comorbidities, and lower perceived cognitive and physical health status. CONCLUSIONS: Randomized participants had excellent adherence overall. Retention rates in the trial were better than would be expected without the adherence intervention, especially among those participants who may have been at higher risk for dropping out of the study. This suggests that a systematic, theoretically based adherence strategy should be further tested in clinical trial settings in which lower adherence is a problem.

Aged↗
PubMed1991

A community-based feasibility study using wheat bran fiber supplementation to lower colon cancer risk.

METHODS: In this feasibility study, free-living older adults (n = 180; means = 67.5 years old) were randomly assigned to one of three levels of a 3-month standardized compliance enhancement program. RESULTS: Regarding subject compliance with the 18 g/day wheat bran fiber supplement, the high compliance enhancement group had a superior regimen compliance rate (88%) versus the medium and low groups, (66 and 29%, respectively) (P = 0.01), with similar attrition rates. CONCLUSION: No significant gastrointestinal side effects and changes in body weight were reported. For similar efficacy, the comprehensive compliance enhancement group had the greatest cost effectiveness.

Adult↗
PubMed1991

A criterion for the adequacy of a simple design when a complex model will be used for analysis.

Sample size computations for relatively complex analyses, such as multiple linear regression, are made difficult by the fact that various quantities that are required by the usual formulas will not be available until the completion of the trial. This fact makes sample size justifications in the design phase of the trial more tenuous than one would like. Here it is shown that for randomized clinical trials it usually suffices to compute sample size on the basis of a simpler model for the analysis than that which will actually be used. Therefore, standard formulas generally provide valid, although possibly inefficient, sample size determinations.

Clinical Trials as Topic↗
PubMed1990

Effects of dietary wheat bran fiber on rectal epithelial cell proliferation in patients with resection for colorectal cancers.

A preponderance of carcinogenesis studies in rodents and epidemiologic studies in humans suggests a potential role of dietary fiber in the prevention of colorectal cancer. Recently, wheat bran fiber used as a dietary supplement has been shown to decrease the growth of rectal adenomatous polyps in patients with familial polyposis; however, few studies of high-risk human populations have been attempted to determine the effects of dietary fiber supplementation on markers of carcinogenesis in the colon or rectum. We have designed a one-arm study to evaluate the effects of dietary supplementation with wheat bran fiber [i.e., 13.5 g/day for 8 wk; after 1 mo, 2 g/day (compliance evaluation period)] on [3H]thymidine rectal mucosa cell labeling (i.e., percent of epithelial cells incorporating [3H]thymidine into DNA in intact rectal crypt cells over a 90-min exposure as well as in minced rectal biopsy tissue over a 24-hr exposure) in rectal biopsy specimens. The biopsy specimens were obtained at sigmoidoscopy in 17 compliant patients with a history of resected colon or rectal cancer. We categorized patients as having initially low or initially high [3H]thymidine-labeling indices (i.e., percent of mucosa cells that incorporate [3H]thymidine into DNA during 1.5- or 24-hour in vitro incubations) by using the median baseline labeling index as a cutoff between high and low values. On the basis of a chi-square test used to identify patients with a statistically significant (P less than .001) change, six of the eight patients who initially had high 24-hour outgrowth labeling indices showed a significant decrease in the rectal mucosa biopsy specimens obtained after treatment. An overall 22% decrease was observed in rectal mucosa cell biopsy specimens obtained at study termination (P less than .001). Of the eight patients with initially high total [3H]thymidine-labeling indices in crypt organ culture, four had a significant (P less than .001) decrease from baseline values, one had a significant increase, and three showed no change following the fiber intervention. The wheat bran fiber dietary supplement of 13.5 g/day was well tolerated by this group of older (54-70 yr) patients. Although the [3H]-thymidine labeling index data suggest that the wheat bran fiber supplement can inhibit DNA synthesis and rectal mucosa cell proliferation in high-risk patients, the results of this small pilot study should not be overinterpreted vis à vis the potential role of wheat bran fiber as a chemopreventive agent for colorectal cancer.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗
PubMed1989

Beyond the thrifty gene: metabolic implications of prehistoric migration into the New World.

Several models have been proposed to explain the high prevalence of non-insulin dependent diabetes mellitus (NIDDM) and other diseases among New World populations. This paper examines the implications of a northern hunting adaptation (reliance on animal foods, seasonal shortages) in terms of energy digestion, absorption, metabolism and storage. Physiologic adaptations to a high protein, moderate fat, low carbohydrate diet are then examined in the context of agriculturally-based subsistence systems and in industrialized societies. Specific metabolic pathways, consistent with the work of both Neel and Weiss, are identified as fruitful areas for further research regarding genetic variants in New World populations.

Diabetes Mellitus, Type 2↗
PubMed1988

Pharmacokinetics and metabolism of retinol administered at a chemopreventive level to normal subjects.

Thirteen subjects between the ages of 50 years and 70 years were administered a daily 25,000 IU dose of retinol for 9 months. Two subjects experienced mild skin dryness, headaches, and/or alopecia. There were no significant changes in serum chemistries. High performance liquid chromatography assays for plasma retinol revealed no evidence of drug accumulation; however, there was a significant increase in the plasma concentration-versus-time curve for retinyl palmitate concentrations between the first and subsequent sampling days (P = 0.009). The mean skin retinol and retinyl palmitate concentrations in 7 retinol-treated subjects (131.7 and 15.9 ng/g, respectively) were not significantly different from those observed in 13 age-matched controls (118.9 and 25.5 ng/gm, respectively).

Adipose Tissue↗
PubMed1987

Dietary change and plasma glucose levels in an Amerindian population undergoing cultural transition.

Dietary change among adult Dogrib Indians of the Northwest Territories, Canada, is examined in conjunction with differences in mean glucose levels among more acculturated-less acculturated settlements. There are significant differences in the intake components derived from non-traditional foods by community and by age. However, the traditional food base is stable. This pattern suggests that dietary acculturation may initially consist of the addition of new foods to a stable traditional dietary, rather than replacement of traditional foods. The net effect is an increase in caloric intake. Age-sex-adjusted plasma glucose levels among four Dogrib settlements did not differ significantly. Comparison of participants who had been tested in a 1979 investigation of glucose tolerance showed that the current lack of intervillage differences can be attributed to an unexplained decrease of mean plasma glucose in the most acculturated village. Either dietary shift does not influence glucose levels, or, its effect can be detected only in conjunction with some other environmental factor. Among the Dogrib, acculturation-associated dietary changes are clearly present. However, their role in influencing plasma glucose levels still needs to be demonstrated.

Acculturation↗
PubMed1985

A covariance structure model for quantitative genetic research.

In this paper, we have presented a general covariance structure model for quantitative genetic research that incorporates measurement theory, components of variance, and regression theory for specification of structural relations among variance components. Each portion of the general model addresses specific issues important in delineating the genetic etiology of continuous traits. Through specification of a measurement model, genetic and environmental influences can be estimated independently of measurement error. Genetic and environmental sources of variance are defined from familial sampling designs through the components of variance model. Structural relationships among several traits at the genetic or environmental level can be specified through the regression model. The significance of parameters specified in each part of the model can be tested through model comparisons using a likelihood ratio chi-square test. We utilized the general model to test genetic covariance as a source of observed covariation of obesity and glucose tolerance in the Pima Indians. We initially applied the modeling approach using full-sib, half-sib sampling among the Pima with a second application including offspring as well as parental scores. Our initial applications of the methodology suggest that the covariance structure model can be a useful tool in genetic epidemiological research. Through model comparisons, our findings suggest that the association of glucose tolerance and obesity in the Pima is not due to a common set of genes but rather due to non-familial environmental influences. In conclusion, one task important for future research, as we see it, is the application of covariance structure models to other familial sampling designs and the evaluation of the usefulness of this approach through further applications to data.

Arizona↗