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Biomedical subjects

R Wilks

Publications and source records attributed to R Wilks.

At least 55 records · Page 3Linked to original sources
PubMed1997

Relationship between blood pressure and body mass index in lean populations.

Associations between body mass index (BMI) and blood pressure (BP) have been consistently observed, but remain poorly understood. One unresolved question is whether there is a linear relationship across the entire BMI range. We investigated this question among 11,235 adult men and women from seven low-BMI populations in Africa and the Caribbean. We used kernel smoothing and multivariate linear and spline regression modeling to examine gender differences in the relationship and to test for a threshold. Age-adjusted slopes of BP on BMI were uniformly higher in men than women, with pooled slope ratios of 2.00 and 2.20 for systolic and diastolic BPs, respectively. Men displayed no evidence of age modification or nonlinearity in the relationship, and the age-adjusted slope of systolic BP on BMI was 0.90 (95% confidence interval [CI], 0.76 to 1.04). Women demonstrated both age modification and nonlinearity. For both younger (<45 years) and older (45+ years) women, the optimal change point for a single threshold model was found to be 21 kg/m2. Slopes of systolic BP on BMI above this threshold were positive and significant: 0.68 (95% CI, 0.54 to 0.81) and 0.53 (95% CI, 0.29 to 0.76) for younger and older women, respectively. Slopes below the threshold were essentially zero for both groups of women, and the difference between the slopes above and below the threshold was significant for younger women (P=.019). In summary, we observed a threshold at 21 kg/m2 in the relationship between BMI and BP for women but not for men. This contributes to the effort to identify the mechanisms that underlie this relationship and how they differ by gender.

Adult↗
PubMed1997

The prevalence of hypertension in seven populations of west African origin.

OBJECTIVES: This study was undertaken to describe the distribution of blood pressures, hypertension prevalence, and associated risk factors among seven populations of West African origin. METHODS: The rates of hypertension in West Africa (Nigeria and Cameroon), the Caribbean (Jamaica, St. Lucia, Barbados), and the United States (metropolitan Chicago, Illinois) were compared on the basis of a highly standardized collaborative protocol. After researchers were given central training in survey methods, population-based samples of 800 to 2500 adults over the age of 25 were examined in seven sites, yielding a total sample of 10014. RESULTS: A consistent gradient of hypertension prevalence was observed, rising from 16% in West Africa to 26% in the Caribbean and 33% in the United States. Mean blood pressures were similar among persons aged 25 to 34, while the increase in hypertension prevalence with age was twice as steep in the United States as in Africa. Environmental factors, most notably obesity and the intake of sodium and potassium, varied consistently with disease prevalence across regions. CONCLUSION: The findings demonstrate the determining role of social conditions in the evolution of hypertension risk in these populations.

Adult↗
PubMed1997

Prevalence of NIDDM among populations of the African diaspora.

OBJECTIVE: Rates of non-insulin-dependent diabetes mellitus have risen sharply in recent years among blacks in the U.S. and the U.K. Increases in risk have likewise been observed in the island nations of the Caribbean and in urban West Africa. To date, however, no systematic comparison of the geographic variation of NIDDM among black populations has been undertaken. RESEARCH DESIGN AND METHODS: In the course of an international collaborative study on cardiovascular disease, we used a standardized protocol to determine the rates of NIDDM and associated risk factors in populations of the African diaspora. Representative samples were drawn from sites in Nigeria, St. Lucia, Barbados, Jamaica, the United States, and the United Kingdom. A total of 4,823 individuals aged 25-74 years were recruited, all sites combined. RESULTS: In sharp contrast to a prevalence of 2% in Nigeria, age-adjusted prevalences of self-reported NIDDM were 9% in the Caribbean and 11% in the U.S. and the U.K. Mean BMI ranged from 22 kg/m2 among men in West Africa to 31 kg/m2 in women in the U.S. Disease prevalence across sites was essentially collinear with obesity, pointing to site differences in the balance between energy intake and expenditure as the primary determinant of differential NIDDM risk among these populations. CONCLUSIONS: In ethnic groups sharing a common genetic ancestry, these comparative data demonstrate the determining influence of changes in living conditions on the population risk of NIDDM.

Adult↗
PubMed1996

Obesity in the Caribbean.

People of African origin who live in the Caribbean share a common genetic heritage but live in socioeconomic environments that diverge widely. A cross-cultural study of males and females from Jamaica, St. Lucia and Barbados investigated the prevalence of hypertension and its environmental determinants. Standardized measurement techniques allowed comparable measurements of weight, height, waist and hip circumferences, and blood pressure. The population values for body mass index (BMI), per cent overweight (males BMI > or = 27.8 kg/m2; females BMI > or = 27.3 kg/m2) and per cent obese (males BMI > or = 31.1 kg/m2; females BMI > or = 32.3 kg/m2) are presented. Prevalence of hypertension is based on the age-adjusted total population. The gradient in per capita gross national product in Jamaica, St. Lucia and Barbados parallels the gradient in the proportions of population in those countries who are obese. BMI explained 26% of the variance in blood pressure in females and 13% in males. Obesity is a significant problem in the Caribbean, as it is in many other developing countries, and it is associated with a high prevalence of hypertension, particularly in women.

Body Composition↗
PubMed1996

Obesity in peoples of the African diaspora.

People of African descent in the Caribbean and the USA originated from the Bight of Benin in West Africa. Although these populations share a common genetic heritage, they now live under different socioeconomical conditions. Assuming genetic similarity, a cross-cultural examination of these peoples in West Africa, the Caribbean and the USA may attenuate the effect of genetic factors and allow the assessment of environmental contributions to a biological outcome. We carried out an epidemiological survey to determine the prevalence of hypertension and the contribution of risk factors to the variation in blood pressure. We measured the height, weight, waist and hip circumferences, and blood pressure of adults in Nigeria, Cameroon, Jamaica, St. Lucia, Barbados and the USA. In urban populations there was a trend towards increasing weight, height, body mass index, and proportions of those overweight and obese going from West Africa to the USA, with the Caribbean being intermediate. The prevalence of hypertension lay on a similar gradient. Given a common genetic susceptibility, urbanization and western acculturation are therefore associated with increasing hypertension and obesity.

Adult↗
PubMed1996

Standardization of blood pressure measurement in an international comparative study.

In the context of a collaborative study on the epidemiology of hypertension in populations of West African origin procedures for standardization of the measurement of blood pressure were evaluated. Comparisons of mean levels of blood pressure, which in large part determine prevalence rates, are highly sensitive to differences in technique. While rotating a single field team may be the ideal approach to multisite studies, it is not practical in international collaborative research. Appropriate techniques to standardize multiple teams over a long period of time have not been well developed, however. In the present study 8981 individuals were examined in eight sites in six countries with the standard mercury sphygmomanometer. An evaluation of the effectiveness of central training, site visits, monitoring of digit preference, and the use of an electronic device for internal standardization is described. In all but one of the sites reliability was high and comparable to the observers at the Coordinating Center. Digit preference for the entire set of measurements was limited (frequency of terminal zero = 23.5% for systolic and 28.9% for diastolic readings) and could be shown to have virtually no effect on prevalence rates or correlation estimates. Mean differences among observers within a given site and between sites were small (+/- 0-5 mmHg). While logistically complex, these methods can provide the basis for standardization in international comparative blood pressure surveys.

Adult↗
PubMed1996

A case-control study of risk factors for seropositivity to human T-lymphotropic virus type I (HTLV-I) in Jamaica.

BACKGROUND: We investigated behavioural and environmental risk factors for seropositivity to human T-lymphotropic virus type I (HTLV-I). METHODS: A nested case-control study of 201 HTLV-I seropositive subjects and 225 age- and sex-matched seronegative controls was performed using questionnaire data from the enrollment visit of a cohort study in 1987-1988. HTLV-I serostatus was confirmed using enzyme-linked immunosorbent assay (ELISA) and Western blot. RESULTS: Among women, the number of lifetime sexual partners (P < 0.05, chi 2 trend) and the number of different men fathering a child by the woman (P < 0.06, chi 2 trend) were associated with HTLV-I seropositivity. Use by the female subject of an intrauterine device (IUD) was associated with an increased risk of seropositivity (odds ratio (OR) = 2.67, 95% confidence interval (CI): 1.13-6.23); condom use was rare in this population. Among male subjects, a larger number of lifetime sexual partners was also associated with HTLV-I seropositivity (P < 0.05, chi 2 trend). No association was found between HTLV-I seropositivity and educational attainment, income, or occupation. Having been breastfed as a child or receipt of a blood transfusion had elevated but imprecise OR due to very high and low prevalence of the risk factors, respectively. Several variables relating to insect or animal exposure showed no association with HTLV-I seropositivity. CONCLUSIONS: These data confirm that heterosexual intercourse is a major route of HTLV-I transmission, but do not support suggestions of insect or environmental vectors.

Adult↗
PubMed1996

Health effects of human T-lymphotropic virus type I (HTLV-I) in a Jamaican cohort.

BACKGROUND: Other than adult T-cell leukaemia (ATL) and HTLV-I associated myelopathy (HAM), the health effects of infection with human T-lymphotropic virus type I (HTLV-I) are not well defined. METHOD: A cohort of 201 confirmed HTLV-I seropositive Jamaican food service workers and 225 seronegative controls of similar age and sex from the same population was examined. A health questionnaire, physical examination, and laboratory tests were performed at enrollment into the cohort in 1987-1988. RESULTS: One of 201 HTLV-I seropositives, but no controls were diagnosed with HAM, for a prevalence of 0.5% (95% confidence interval) (CI) 0.01-2.7%); no cases of ATL were diagnosed. While there was no difference in current symptoms, the HTLV-I seropositive group was more likely to report a past medical history of hepatitis or jaundice (OR = 3.49, 95% CI: 0.93-13.08), malaria (OR = 2.13, 95% CI: 0.96-4.73), and dengue fever (OR = 1.37, 95% CI: 0.82-2.29); however, these differences were of borderline statistical significance. Low income HTLV-I seropositive women had lower body weight (P < 0.01) and body mass index (P < 0.009) than their seronegative counterparts; similar differences were seen in the smaller male group. A trend toward higher prevalence of severe anaemia (haemoglobin < 10 g/dl) (12.6% versus 7.7%, P < 0.105) and a significantly lower prevalence of eosinophilia (1.0% versus 6.3%, P < 0.004) was seen among HTLV-I seropositives compared to controls. CONCLUSIONS: Although most HTLV-I seropositives are asymptomatic, HAM may be diagnosed in approximately 0.5% of carriers. Chronic HTLV-I infection may also exert subtle effects on body mass and haematological parameters.

Adult↗
PubMed1996

Angiotensinogen and blood pressure among blacks: findings from a community survey in Jamaica.

OBJECTIVE: To examine the association between blood pressure, angiotensinogen levels, angiotensin converting enzyme activity and polymorphisms of the angiotensinogen and angiotensin converting enzyme genes in a population-based sample. METHOD: Five hundred participants were recruited in a house-to-house survey of three communities in metropolitan areas of Kingston and St Andrew, in Jamaica. Demographic data, anthropometric and blood pressure measurements were obtained for each participant during a brief clinic visit. Circulating levels of angiotensinogen and angiotensin converting enzyme activity were measured in venous blood samples. Polymorphisms of the angiotensinogen and angiotensin converting enzyme genes were determined. RESULTS: A weak association between angiotensinogen level, angiotensin converting enzyme activity and blood pressure was identified in this population, but substantial joint effect of angiotensin converting enzyme activity and angiotensinogen level on blood pressure was apparent. Variants of the angiotensinogen gene had inconsistent effects on blood pressure and on the risk of hypertension. Angiotensinogen level and angiotensin converting enzyme activity were significantly related to several measures of obesity, including body mass index, waist circumference and skin fold thickness. CONCLUSION: The angiotensinogen and angiotensin converting enzyme genetic variants which were studied appear to have only a modest relationship with blood pressure and associated anthropometric risk factors among blacks.

Adult↗
PubMed1996

A comparative study of hypertension prevalence, awareness, treatment and control rates in St Lucia, Jamaica and Barbados.

BACKGROUND: Cardiovascular diseases represent the most common cause of death in the English-speaking Caribbean, and hypertension represents the most important predisposing condition. However, direct between-country comparative studies in the Caribbean have not previously been undertaken. OBJECTIVE: To obtain estimates of hypertension prevalence, awareness, treatment and control in three countries in the Caribbean. DESIGN: Population-based samples of adults aged 25-74 years in St Lucia, Barbados and Jamaica were surveyed regarding their cardiovascular health and their blood pressures were measured using a highly standardized protocol. A reference site was available from a collaborative study among blacks in metropolitan Chicago, Illinois, USA. RESULTS: At the 160/95 mmHg threshold, age-adjusted hypertension prevalence estimates for Jamaica, St Lucia and Barbados were 17.5, 18.3 and 21.5%, respectively, and 24.7, 26.9 and 27.9%, respectively, at the 140/90 mmHg threshold. The corresponding estimate for the Chicago site at the 140/90 mmHg threshold was 33.2%. The gradient in prevalence resembled the gradient in body mass index (25.7 kg/m2 in Jamaica to 29.3 kg/m2 in the USA). At the 160/95 mmHg threshold, the proportion of all hypertensives who were aware of their disease, pharmacologically treated and controlled was highest in Barbados (90, 85 and 72%, respectively) and lowest in St Lucia (74, 59 and 35%, respectively). Men, particularly those aged less than 55 years, were less likely to have their hypertension treated and controlled. CONCLUSIONS: Compared with estimates from earlier independent surveys, considerable progress has been made in hypertension detection and control in these countries, which should lead to sizable reductions in the burden of cardiovascular disease.

Adult↗
PubMed1996

Development of food frequency questionnaires in three population samples of African origin from Cameroon, Jamaica and Caribbean migrants to the UK.

OBJECTIVES: To develop the methods for assessment of food and nutrient intake using standardized food frequency questionnaires (FFQ) in three African origin populations from Cameroon, Jamaica and Caribbean migrants to the United Kingdom. DESIGN: Cross-sectional assessment of diet from a representative sample in each site, using either a 2-day food diary or a 24-h recall method to determine foods for inclusion on the food frequency questionnaire. SETTING: A rural and urban site in Cameroon, Evodoula and Cite Verte in Yaounde, respectively; a district in Kingston Jamaica; African-Caribbeans living in central Manchester, UK. SUBJECTS: Aged 25-79 years, 61 from the Cameroonian urban site, 62 from the village site; 102 subjects from Jamaica (additional analysis on a subsample of 20): 29 subjects from Manchester, UK. MAIN OUTCOME MEASURES: Foods contributing to nutrients in each site to allow the development of a FFQ. RESULTS: A high response rate was obtained in each site. Comparison of macronutrient intakes between the sites showed that carbohydrate was the most important contributor to energy intake in Jamaica (55%) and the least in rural Cameroon. In rural Cameroon, fat (mainly palm oil) was the most important contributor to energy intake (44%). Manchester had the highest contribution of protein to energy (17%). Foods contributing to total energy, protein, fat and carbohydrate were determined. In rural Cameroon, the top 10 food items contributed 66% of the total energy intake compared to 37% for the top 10 foods in Manchester. Foods contributing to energy were similar in Jamaica and Manchester. Cassava contributed 44% of the carbohydrate intake in rural Cameroon and only 6% in urban Cameroon. One FFQ has been developed for use in both sites in Cameroon containing 76 food items. The FFQ for Jamaica contains 69 foods and for Manchester 108 food items. CONCLUSION: Considerable variations exist within sites (Cameroon) and between sites in foods which are important contributors to nutrient intakes. With careful exploration of eating habits it has been possible to develop standardized, but locally appropriate FFQs for use in African populations in different countries.

Adult↗
PubMed1993

Chromosomal radiosensitivity at intrachromosomal telomeric sites.

Telomeric DNA is composed of highly conserved sequences which are present at the termini of chromosomes as well as at intrachromosomal locations. Here, we studied a Chinese hamster ovary (CHO) cell line, BL-10, with highly stable amplified telomeric DNA at the termini as well as at intrachromosomal locations. We show that intrachromosomal or interstitial telomeric sites in this cell line and in another CHO cell line, HA-I, are radiosensitive in that they are more prone to breakage than would be expected based on the percentage of the genome composed of telomeric sequences. The frequency of breakage at interstitial telomeric sites is 4.3 to 8.3 times higher than that in the CHO genome overall. These conclusions are reached by both conventional cytogenetic analysis of two CHO cell lines which have the same survival rates after exposure to ionizing radiation, and by use of double fluorescence in situ hybridization (FISH) with a pan-telomere-specific probe and a CHO chromosome-specific library in the same metaphase cells after irradiation.

Animals↗
PubMed1991

Detection of early human T-cell lymphotropic virus type I antibody patterns during seroconversion among transfusion recipients.

From a cohort of human T-cell lymphotropic virus type I (HTLV-I) exposed transfusion recipients (N = 71) enrolled in the Jamaican Transfusion Study, 11 were selected for detailed laboratory evaluation. All recipients were followed at monthly intervals for 6 months and then bimonthly up to 1 year for evidence of HTLV-I seroconversion. Without regard to results on screening assays, pretransfusion and posttransfusion samples were tested with two licensed HTLV-1 whole-virus screening enzyme immunoassays (EIAs), recombinant EIAs for antibody against tax (p40x) and p21e envelope, standard whole virus Western blot (WB), WB enhanced with recombinant p21e, and radioimmunoprecipitation assay (RIPA). In the early period posttransfusion, antibody to gag core protein was predominant with anti-p24 generally appearing before anti-p19. Recombinant anti-p21e envelope protein, in EIA and WB format, was frequently the earliest envelope reactivity detected, while anti-gp46 in WB and anti-gp61/68 in RIPA system appeared later. Anti-tax antibodies appeared later in the time course of seroconversion. The whole-virus EIAs were less sensitive than the confirmatory assays. The combination of WB and RIPA or WB enhanced with recombinant p21e appeared equally effective in confirming samples as positive by the Public Health Service two gene group confirmatory algorithm. However, specificity of this assay approach could not be addressed in this study.

Adolescent↗
PubMed1989

Amoebiasis in Jamaica. A forgotten cause of hepato-intestinal disease.

Amoebiasis still occurs in Jamaica. This paper describes the unexpected occurrence of the disease in three adult males, two with colitis and the other with an hepatic abscess. This, to our knowledge, is the first report of amoebiasis in Jamaica for over two decades and serves to underscore the continued need for the inclusion of amoebiasis in the differential diagnosis of unexplained hepato-intestinal disease.

Adult↗