Nish is the Principal investigator and leads the SABRE Study. She is Professor of Clinical Epidemiology based in the Institute of Cardiovascular Science at University College London and, together with Paul McKeigue, was responsible for the Brent part of the baseline studies. Nish has extensively researched and published on ethnic group differences in cardiovascular disease and diabetes.
The Southall and Brent baseline studies were cross-sectional studies conducted between 1989 and 1991, at a time when the majority of first generation South Asian and African Caribbean migrants to the UK were entering middle age. The studies have generated a number of hypotheses regarding the causes of ethnic group differences in cardiovascular risk factors and the pathogenesis of cardiovascular disease.
The baseline studies were the first to report the high prevalence of the insulin resistance or cardiometabolic syndrome in association with a striking tendency to central obesity in British South Asian migrants- these findings were common to Hindus, Sikhs and Muslims. These results suggested that insulin resistance is the underlying cause of their increased susceptibility to coronary heart disease and stroke (1,2).
African Caribbeans, on the other hand, were as dysglycaemic but less hyperinsulinaemic than South Asians. They were not centrally obese suggesting that the causes of diabetes in African Caribbeans may be different from those in South Asians and this might also explain why coronary heart disease mortality in African Caribbeans is low, despite the high prevalence of diabetes and hypertension (1,2). Their more favourable lipid profiles were thought to be related to body fat distribution (5).
Resting and ambulatory blood pressure recordings in a subgroup of Europeans and African Caribbeans, demonstrated that resting blood pressures were substantially higher in the African Caribbeans and that this may be enough to explain excess stroke mortality in African Caribbean women, but not in men. Smaller declines in nocturnal blood pressure may contribute to the excess of hypertensive target organ damage in African Caribbeans (3).
A presentation about some of these findings:Baseline findings presentation
SABRE was first started in order to understand why some people are more likely than others to suffer from diabetes, coronary heart disease and strokes. At the time very little was known about whether people of different ethnicities might be more or less likely to suffer these disorders.
We now know, partly as a result of the first SABRE study, that there are large differences in risk of coronary heart disease and strokes between different ethnic groups in the UK, as well differences in risk factors such as diabetes, blood pressure and levels of ‘good’ and ‘bad’ blood fats. But we still don’t know why these ethnic differences happen.
From the first study we had collected lots of very valuable information about health in mid-life (participants were aged between 40 and 69 at the time). From that time, we have blood measurements (such as glucose, insulin and fats), blood pressure, information that participants gave us by filling in a questionnaire about their health and lifestyle as well as many measurements of where body fat was stored.
This recent follow-up of health means that we can use the information from 20 years ago to see
- which measurements predict good health in older age
- which measurements predict diabetes, heart disease or strokes or any serious disabilities or other health problems
- who has pre-diabetes or early signs of disorders of the heart and circulation that they are not aware of
- whether we can explain why some people developed these disorders and others didn’t
The heart is a pump which makes sure that all the tissues of the body receive a blood supply containing oxygen and nutrients. Like all pumps, the heart may become less efficient as it gets older and eventually it may not be able to keep up with the demands of the body- this is called heart failure, and although there are treatments available for heart failure, it is a serious and unpleasant disorder . Heart failure is more likely to happen when people have already had a heart attack and it may also be related to high blood pressure and diabetes.
The 3 dimensional echo scans that participants underwent at the SABRE follow-up are new and tell us about early signs of heart failure. We found that African Caribbeans and Europeans were very similar with regard to the size of the left ventricle (this is the part of the heart which pumps blood around the whole body and if it becomes enlarged it may be an early sign that the heart is under strain (picture of heart here)). On the other hand, in Indian Asians the left ventricle was on average a little smaller in relation to body size than in Europeans, but at the same time their heart muscles needed more oxygen to work efficiently.
Very few SABRE participants had actual heart failure at the 2008-2011 follow-up. However, as participants are moving towards older age, they are more at risk of this disorder. the next follow-up study (2014-17) will focus on heart failure, using these measurements and some measurement made 20 years ago to understand why some people are at particular risk of heart failure in later life.
For more information about heart failure, visit the British Heart Foundation.
As expected, numbers of strokes increase as people get older in all ethnic groups. Interestingly, in study participants who were free of diabetes in 1988-91, there were no ethnic differences in the proportions of people who developed strokes during follow-up. However, when we looked at people who had diabetes at the time of the baseline studies in 1988-91, we found that both Indian Asians and African Caribbeans with diabetes were twice as likely to develop strokes as Europeans with diabetes.
We also found that the MRI brain scans showed that African Caribbeans had more early signs of blood vessel problems in the brain than Europeans and that this was particularly related to having diabetes. These findings suggests that diabetes is especially harmful to people in our ethnic minorities, and although we don’t yet know why this is, it may be because the blood vessels in the brain are more affected by diabetes and pre-diabetes making them less able to cope with day to day changes in blood pressure – more research is needed to confirm this.
(MRI scans from the Indian Asians haven’t yet been fully analysed… coming soon)
For more information about stroke, visit The Stroke Association.
An astonishing number of people have developed diabetes over the last 20 years. By the age of 70, almost 1 in 3 Indian Asians and African Caribbeans and 1 in 6 Europeans will have diabetes. There is a steady rise in the numbers of people with diabetes even into older age. This is hugely important. We know that diabetes affects every system in the body and that it can shorten people’s lives, particularly because it can cause heart disease and stroke. Not only does diabetes shorten peoples’ lives, it can harm the quality of their lives too.
Our findings leads us to ask why Indian Asians and African Caribbeans have more diabetes than Europeans?
Type 2 diabetes is usually thought to be a disorder caused by overweight, particularly when fat accumulates around the waist. When we set out on the 20 year follow-up study we had proposed that it would be the patterns of where fat is deposited that would explain the ethnic differences in the amount of diabetes. Was this true? Yes and no!
As we expected, extra fat around the waist measured 20 years ago (both inside the abdomen and under the skin) is an important predictor of later development of diabetes in everyone and it mostly explains why Indian Asian and African Caribbean women are more at risk than European women. However, extra fat and extra resistance to the effects of insulin in middle age are only part of the reason why Indian Asian and African Caribbean men are more at risk and none of the risk factors that we measured 20 years ago was able to explain all of the extra risk of diabetes in these ethnic groups.
We hope that the next SABRE follow-up(2014-17) will give us some more answers to this question
For more information about diabetes, visit Diabetes UK
Since the baseline data collection, deaths have been flagged by the Office for National Statistics and we have collected data regarding non-fatal coronary and stroke events during 20 years of follow-up to 2011.
Coronary heart disease events occurred in 1256(30%) participants, of these 86% were first-ever events. Fatal Coronary heart disease was the first recorded follow-up event in 159 participants. Indian Asians were most (Hazard ratio(HR): 1.7), and African Caribbeans least(HR:0.64), at risk of coronary events.
Stroke events occurred in 401 participants during follow-up, of which 371(93%) were first ever strokes. Fatal stroke was the first recorded follow-up event in 48 participants. African Caribbeans had the highest(HR:1.5) and Europeans(HR:1) the lowest rates of stroke.
Analyses of baseline characteristics as predictors of these events have indicated that diabetes and dysglycaemia are particularly toxic in South Asians and African Caribbeans in whom stroke was 2.5-3 times more likely to occur in association with diabetes compared with Europeans (References 17, 18, 24). This extra diabetes-related ‘toxicity’ was also present, but to a lesser extent for South Asians in association with incident coronary heart disease, in whom diabetes was associated with a 40% excess risk. Other measured baseline risk factors did not explain the ethnic differentials in stroke and coronary disease.
Further study of factors acting across the life course, together with genetic and epigenetic studies could elucidate mechanisms underlying ethnic differences and define key time points for preventive interventions. These findings suggest that early glycaemic control plus intervention to control blood pressure in these high risk populations may be paramount in the prevention of stroke and coronary heart disease.
Further information on diabetes can be found through the following links:
Diabetes UK: www.diabetes.org.uk/
Juvenile Diabetes Research Foundation: www.jdrf.org.uk/
Diabetes Research Network: www.ukdrn.org/
Diabetes – NHS Choices: http://www.nhs.uk/Conditions/Diabetes/Pages/Diabetes.aspx
British Heart Foundation: www.bhf.org.uk/