Biomedical subjects
John S Yudkin
Publications and source records attributed to John S Yudkin.
Diabetes care in sub-Saharan Africa.
The increasing numbers of people with type 2 diabetes is a worldwide concern. It presents an added challenge in sub-Saharan Africa, where diabetes must compete for resources with communicable diseases. A scarcity of financial resources and appropriate staff mean that many people with type 2 diabetes have complications and that those with type 1 diabetes have an extremely short life-expectancy, whether or not they have been diagnosed with the disorder. We review the current evidence on diabetes care in sub-Saharan Africa and propose an 11-point action plan to address this problem in the region.
Visceral and truncal subcutaneous adipose tissue are associated with impaired capillary recruitment in healthy individuals.
CONTEXT: Central adiposity is associated with cardiovascular risk independently of total adiposity. Microvascular dysfunction is thought to contribute to obesity-associated insulin resistance and hypertension and may thus link central adiposity with cardiovascular risk. OBJECTIVE: Our objective was to investigate how body fat distribution relates to microvascular function and the role of adipocytokines in these relationships. DESIGN, SETTING, AND PARTICIPANTS: We cross-sectionally studied 51 healthy adults and 29 of their prepubertal children born at the VU University Medical Center in Amsterdam. MAIN OUTCOME MEASURES: We measured visceral and abdominal sc adiposity with magnetic resonance imaging and truncal and peripheral sc adiposity with skinfold thickness. Postocclusive skin capillary recruitment was assessed with videomicroscopy. Concentrations of C-reactive protein, IL-6, and TNF-alpha were combined in an inflammation score. RESULTS: In adults, visceral adipose tissue and trunk/extremity skinfold ratio were inversely associated with capillary recruitment (partial correlation coefficients, -0.32, P = 0.03, and -0.37, P < 0.01, respectively). The inflammation score was inversely associated with capillary recruitment (r = -0.50; P < 0.01) and statistically explained 41% of the association between visceral adipose tissue and capillary recruitment. In children, trunk/extremity skinfold ratio was inversely associated with capillary recruitment (r = -0.49; P = 0.01), but other measures of adiposity were not. CONCLUSION: Our data in adults suggest a role for visceral adiposity and its associated proinflammatory state in capillary dysfunction and its possible sequelae such as hypertension and insulin resistance. Also, our findings in children and adults suggest that truncal sc adiposity is detrimental for capillary perfusion and that this process may start before puberty.
Confounders in chronic stress at work and metabolic syndrome.
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Insight into the nature of the CRP-coronary event association using Mendelian randomization.
BACKGROUND: It is unclear wheather the association between C-reactive protein (CRP) and incident coronary events is free from bias and confounding. Individuals homozygous for a +1444C>T polymorphism in the CRP gene have higher circulating concentrations of CRP. Since the distribution of this polymorphism occurs at random during gamete formation, its association with coronary events should not be biased or confounded. METHODS: We calculated the weighted mean difference in CRP between individuals with variants of the +1444C>T polymorphism in the CRP gene among 4,659 European men from six studies (genotype-intermediate phenotype studies). We used this difference together with data from previous observational studies to compute an expected odds ratio (OR) for non-fatal myocardial infarction (MI) among individuals homozygous for the T allele. We then performed four new genetic association studies (6,201 European men) to obtain a summary OR for the association between the +1444C>T polymorphism and non-fatal MI (genotype-disease studies). RESULTS: CRP was 0.68 mg/l [95% confidence interval (95% CI) 0.31-1.10; P = 0.0001] higher among subjects homozygous for the +1444-T allele, with no confounding by a range of covariates. The expected ORs among TT subjects for non-fatal MI corresponding to this difference in CRP was 1.20 (95% CI 1.07-1.38) using the Reykjavik Heart study data and 1.25 (1.09-1.43) for all observational studies to 2004. The estimate for the observed adjusted-OR for non-fatal MI among TT subjects was 1.01 (95% CI 0.74-1.38), lower than both expected ORs. CONCLUSIONS: A common CRP gene polymorphism is associated with important differences in CRP concentrations, free from confounding. The null association of this variant with coronary events suggests possible residual confounding (or reverse causation) in the CRP-coronary event association in observational studies, though the confidence limits are still compatible with a modest causal effect. Additional studies of genotype (or haplotype) and coronary events would help clarify whether or not the link between CRP and coronary events in observational studies is causal.
Assessing health systems for type 1 diabetes in sub-Saharan Africa: developing a 'Rapid Assessment Protocol for Insulin Access'.
BACKGROUND: In order to improve the health of people with Type 1 diabetes in developing countries, a clear analysis of the constraints to insulin access and diabetes care is needed. We developed a Rapid Assessment Protocol for Insulin Access, comprising a series of questionnaires as well as a protocol for the gathering of other data through site visits, discussions, and document reviews. METHODS: The Rapid Assessment Protocol for Insulin Access draws on the principles of Rapid Assessment Protocols which have been developed and implemented in several different areas. This protocol was adapted through a thorough literature review on diabetes, chronic condition management and medicine supply in developing countries. A visit to three countries in sub-Saharan Africa and meetings with different experts in the field of diabetes helped refine the questionnaires. Following the development of the questionnaires these were tested with various people familiar with diabetes and/or healthcare in developing countries. The Protocol was piloted in Mozambique then refined and had two further iterations in Zambia and Mali. Translations of questionnaires were made into local languages when necessary, with back translation to ensure precision. RESULTS: In each country the protocol was implemented in 3 areas--the capital city, a large urban centre and a predominantly rural area and their respective surroundings. Interviews were carried out by local teams trained on how to use the tool. Data was then collected and entered into a database for analysis. CONCLUSION: The Rapid Assessment Protocol for Insulin Access was developed to provide a situational analysis of Type 1 diabetes, in order to make recommendations to the national Ministries of Health and Diabetes Associations. It provided valuable information on patients' access to insulin, syringes, monitoring and care. It was thus able to sketch a picture of the health care system with regards to its ability to care for people with diabetes. In all countries where this tool was used the involvement of local stakeholders resulted in the process acting as a catalyst in bringing diabetes to the attention of the health authorities.
To: Gerstein HC, Pogue J, Mann JFE, Lonn E, Dagenais GR, McQueen M, Yusuf S, for the HOPE investigators (2005) The relationship between dysglycaemia and cardiovascular and renal risk in diabetic and non-diabetic participants in the HOPE study: a prospective epidemiological analysis. Diabetologia 48:1749-1755.
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PROactive study.
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TNF-alpha levels are associated with skin capillary recruitment in humans: a potential explanation for the relationship between TNF-alpha and insulin resistance.
The mechanism by which TNF-alpha (tumour necrosis factor-alpha) may cause insulin resistance is not clear. On the basis of experiments in rats, TNF-alpha has been suggested to cause defects in capillary function, with a decreased access of insulin and glucose to tissues. To test this hypothesis in humans, we assessed serum TNF-alpha concentrations, skin capillary recruitment and insulin sensitivity in a group of 37 healthy adults. In addition, we measured these variables in 21 of their prepubertal children. Serum TNF-alpha levels were measured by sandwich enzyme immunoassay, and insulin sensitivity was assessed with the hyperinsulinaemic euglycaemic clamp technique. Capillary recruitment during post-occlusive reactive hyperaemia was evaluated by videomicroscopy. In the adults, serum TNF-alpha levels were associated with both capillary recruitment (r=-0.40, P=0.02) and insulin sensitivity (r=-0.33, P=0.05). In addition, capillary recruitment was associated with insulin sensitivity (r=0.34, P=0.04). Regression analysis showed that the association between TNF-alpha and insulin sensitivity [-0.527 mg.kg(-1) of body weight.min(-1) per pmol/l per pg/ml TNF-alpha (95% confidence interval, -1.066 to 0.011); P=0.05] decreased by 30% after adjustment for capillary recruitment. In the children, neither capillary recruitment (r=0.33, P=0.2) nor insulin sensitivity (r=-0.24, P=0.4) was significantly associated with TNF-alpha. In conclusion, in adults, but not in children, serum TNF-alpha levels are associated with capillary recruitment during post-occlusive hyperaemia, which, in part, can explain the relationship between TNF-alpha and insulin resistance. Our data suggest that these relationships are initiated during growth from childhood to adulthood.
A theme issue by, for, and about Africa: tackling the challenge of diabetes.
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Haematocrit, type 2 diabetes, and endothelium-dependent vasodilatation of resistance vessels.
AIMS: In conditions such as type 2 diabetes, hypertension, and smoking, in which haematocrit (Hct) tends to be higher, endothelial function is impaired. In vitro, haemoglobin neutralizes nitric oxide very effectively. Whether red blood cells participate in the regulation of endothelial function in vivo has not been established. METHODS AND RESULTS: Clinical and haematological parameters and forearm blood flow responses to acetylcholine (ACh) and sodium nitroprusside (SNP) were measured in 84 type 2 diabetic patients and 19 control subjects. Diabetics showed blunted dose-response curves to both SNP and ACh. In diabetics, across quartiles of Hct, ACh blood flow responses were progressively lower (881+/-96, 652+/-81, 513+/-54, 307+/-46%, P</0.0001), and maximal SNP responses tended to be lower (706+/-72, 578+/-61, 607+/-69, 499+/-53%, P=0.06) despite similar age, body mass index, glycated haemoglobin (HbA(1c)), blood pressure, serum total and HDL-cholesterol levels, indices of insulin sensitivity, and markers of inflammation. After normalizing the ACh response for the SNP response (ACh/SNP ratio), a progressive reduction across Hct quartiles (1.54+/-0.23, 1.22+/-0.15, 0.93+/-0.09, 0.66+/-0.09, P<0.0001) was still observed, with patients in the III and IV quartile showing a blunted response compared with controls (1.44+/-0.08). Both in diabetics and controls, the ACh/SNP ratio was reciprocally related to Hct (r=-0.46 and r=-0.66, respectively, P<0.002 for both). This association was independent of comorbidities, gender, metabolic control, plasma lipids, or concomitant treatments, was stronger in the subjects with preserved endothelium-dependent dilatation, and was unchanged when haemoglobin replaced Hct. CONCLUSION: Both in diabetics and non-diabetics, haematocrit is inversely related to small vessel endothelium-dependent dilatation. Thus, in addition to blood rheology, a direct negative effect on nitric oxide availability might explain the link between high Hct and cardiovascular disease.
Access to care for patients with insulin-requiring diabetes in developing countries: case studies of Mozambique and Zambia.
OBJECTIVE: The objective of this study was to assess the barriers to care for patients with insulin-requiring diabetes in Mozambique and Zambia. RESEARCH DESIGN AND METHODS: We used the Rapid Assessment Protocol for Insulin Access to collect information through interviews, discussions, site visits, and document reviews. Government organizations, health facilities, care givers, and patients were asked about care for people with insulin-requiring diabetes. Between 100 and 200 interviews/discussions per country were undertaken in and around the capital city and the regional capital and in a rural area. RESULTS: Insulin was present in both countries in sufficient quantities, although the financial burden for health services and patients meant that problems with supply exist. There are problems with quantification of needs and equitable distribution of insulin. Problems with availability of syringes and testing equipment were noted, particularly in Mozambique. This lack of tools and infrastructure for diagnosis and follow-up coupled with low levels of health care worker training and lack of diagnostic reagents resulted in a substantial risk of misdiagnosis or failure to detect diabetes. The estimated prevalence of insulin-requiring diabetes differs more than 10-fold between urban and rural areas in Mozambique and 4-fold between Mozambique and Zambia, suggesting that problems in diagnosis and care result in substantial worsening of prognosis for such patients. CONCLUSIONS: Insulin is necessary but not sufficient to improve prognosis for diabetic patients. A Rapid Assessment Protocol methodology can be used to define problems in health care delivery for diabetes. Proper care for insulin-requiring diabetes necessitates health systems able to provide trained personnel, medicines in sufficient quantity, and diagnostic and monitoring facilities.
The Y-Y paradox.
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Regional body composition as a determinant of arterial stiffness in the elderly: The Hoorn Study.
OBJECTIVE: To estimate the relation of precisely measured regional body composition with peripheral and central arterial stiffness in the elderly. METHODS: We investigated 648 participants (mean age 69.0 +/- 6.0 years) of the Hoorn Study, a population-based cohort study. Trunk fat, leg fat, trunk lean and leg lean mass were distinguished by dual-energy X-ray absorptiometry. We used ultrasound to measure the distensibility and compliance of the carotid, femoral and brachial arteries, and carotid Young's elastic modulus, as estimates of peripheral stiffness. As estimates of central stiffness we measured carotid-femoral transit time, aortic augmentation index and systemic arterial compliance. RESULTS: After adjustment for sex, age, height, mean arterial pressure, leg lean and leg fat mass, a larger trunk fat mass was consistently associated with higher peripheral arterial stiffness (standardized beta (beta) of mean Z-scores of all three large arteries -0.24, P < 0.001). In contrast, larger leg fat mass (beta = 0.15, P = 0.009) and leg lean mass (beta = 0.09, P = 0.20) were associated with lower peripheral arterial stiffness. Trunk or leg fat mass were not associated with central arterial stiffness. Leg lean mass, however, was consistently associated with lower central arterial stiffness (beta = 0.29, P < 0.001). CONCLUSIONS: Trunk fat mass may have adverse effects on peripheral, but not on central arterial stiffness, while leg fat was not harmful and may have a slight protective effect. Larger leg lean mass was the most important determinant of lower central arterial stiffness. These results provide a pathophysiological framework to explain not only the higher cardiovascular risk in individuals with larger trunk fat mass, but also the reduced cardiovascular risk in individuals with larger leg lean and fat mass.
Effect of Interleukin-6 promoter polymorphisms in survivors of myocardial infarction and matched controls in the North and South of Europe. The HIFMECH Study.
Elevated plasma IL-6 levels have been implicated in the pathogenesis of coronary heart disease. We have investigated the association of two polymorphisms in the promoter of IL-6 (-572G>C and -174G>C) with levels of inflammatory markers and risk of myocardial infarction (MI) in a European study of MI survivors and age-matched controls from two high-risk centres in the North of Europe, and two low risk centres in the South. IL-6 and CRP levels were similar in controls in both regions, but were higher in cases. For the -174G>C polymorphism the rare -174C allele showed a regional difference in allele frequency, being more common in the North European group (0.43 vs 0.28; p < 0.0005), where -174C allele carriers showed an apparent reduced risk of MI compared to -174GG homozygotes (OR 0.53, 95%CI 0.32, 0.86). No such effect was observed in the South or with the -572G>C in either group. Neither genotype was associated with a significant effect on plasma IL-6 levels in either cases or controls. Furthermore, no regional difference was observed in the frequency of the -572G>C SNP, suggesting that these polymorphisms are unlikely to be contributing to the observed increased risk of cardiovascular disease in Northern Europe.
Trunk fat and leg fat have independent and opposite associations with fasting and postload glucose levels: the Hoorn study.
OBJECTIVE: Waist and hip circumferences have been shown to have independent and opposite associations with glucose levels. Waist circumference is positively associated with glucose levels, whereas hip circumference is negatively associated. It is unclear which tissues are involved in the pathophysiological mechanism causing these associations. The main goal was to determine which tissue in the trunk and legs, fat or lean tissue, is associated with measures of glucose metabolism. RESEARCH DESIGN AND METHODS: In 623 participants of the third examination of the Hoorn Study, whole-body dual-energy X-ray absorptiometry was performed to determine fat and lean soft-tissue mass in the trunk and legs. Fasting and 2-h postload glucose levels after 75-g oral glucose tolerance test (OGTT) were determined. After exclusion of known diabetic patients, cross-sectional analyses were performed in 275 men aged 60-87 years (140 with normal glucose metabolism, 92 with impaired glucose metabolism; and 43 with diabetes) and in 281 women (148 with normal glucose metabolism, 90 with impaired glucose metabolism, and 43 with diabetes). RESULTS: Greater trunk fat mass was associated with higher glucose levels after adjustment for age, trunk lean mass, leg lean mass, and leg fat mass. Standardized beta (95% CI) in men were 0.44 (0.25-0.64) for fasting and 0.41 (0.22-0.60) for postload glucose. For women, these values were 0.49 (0.35-0.63) and 0.47 (0.33-0.61), respectively. In contrast, in the same regression models, a larger leg fat mass was associated with lower glucose levels. Standardized beta in men were -0.24 (-0.43 to -0.05) and -0.12 (-0.31 to 0.07) and in women -0.24 (-0.37 to -0.10) and -0.27 (-0.40 to -0.13) for fasting and postload glucose, respectively. In these models, larger leg lean mass was also associated with lower glucose levels but was only statistically significant in men. CONCLUSIONS: If trunk fat is taken into account, accumulation of fat in the legs seems to be protective against a disturbed glucose metabolism, particularly in women. Further research is needed to unravel underlying pathophysiological mechanisms.
Vascular effects of improving metabolic control with metformin or rosiglitazone in type 2 diabetes.
OBJECTIVE: The aim of this study was to test whether vascular reactivity is modified by improving metabolic control and peripheral insulin resistance in type 2 diabetes. RESEARCH DESIGN AND METHODS: In a randomized, double-blind design, we assigned 74 type 2 diabetic patients to rosiglitazone (8 mg/day), metformin (1,500 mg/day), or placebo treatment for 16 weeks and measured insulin sensitivity (euglycemic insulin clamp), ambulatory blood pressure, and forearm blood flow response to 1) intra-arterial acetylcholine (ACh), 2) intra-arterial nitroprusside, 3) the clamp, and 4) blockade of nitric oxide (NO) synthase. RESULTS: Compared with 25 nondiabetic subjects, patients had reduced insulin sensitivity (30 +/- 1 vs. 41 +/- 3 micromol. min(-1). kg fat-free mass(-1); P < 0.001) and reduced maximal response to ACh (586 +/- 42 vs. 883 +/- 81%; P < 0.001). Relative to placebo, 16 weeks of rosiglitazone and metformin similarly reduced fasting glucose (-2.3 +/- 0.5 and -2.3 +/- 0.5 mmol/l) and HbA(1c) (-1.2 +/- 0.3 and -1.6 +/- 0.3%). Insulin sensitivity increased with rosiglitazone (+6 +/- 3 micromol. min(-1). kg fat-free mass(-1); P < 0.01) but not with metformin or placebo. Ambulatory diastolic blood pressure fell consistently (-2 +/- 1 mmHg; P < 0.05) only in the rosiglitazone group. Nitroprusside dose response, clamp-induced vasodilatation, and NO blockade were not affected by either treatment. In contrast, the slope of the ACh dose response improved with rosiglitazone (+40% versus baseline, P < 0.05, +70% versus placebo, P < 0.005) but did not change with either metformin or placebo. This improvement in endothelium-dependent vasodilatation was accompanied by decrements in circulating levels of free fatty acids and tumor necrosis factor-alpha. CONCLUSIONS: At equivalent glycemic control, rosiglitazone, but not metformin, improves endothelium dependent vasodilatation and insulin sensitivity in type 2 diabetes.
Common variants in the thrombomodulin gene as a risk for myocardial infarction in the north of Europe (HIFMECH Study).
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