Cardiovascular diseases and the search for more evidence
Daniel Day Lewis won an Oscar this year for his depiction of Abraham Lincoln’s role in the abolition of slavery in the USA. As I watched Lincoln on the plane crossing the Atlantic, I wondered how many inequalities still exist in health and whether laws are the best way to reduce or abolish these inequalities.
Looking at just cardiovascular diseases, inequalities have been highlighted at local, regional, national and international levels, whether on the basis of gender, age, socioeconomic status or race. We have known about the major risk factors which cause cardiovascular disease for over 50 years, and yet some of these inequalities still pose significant challenges in many parts of the globe. An example from the UK is the recent study showing regional variations in mortality from cardiovascular disease in each electoral ward.
So do we not have enough evidence to act? Do we need to keep producing more research to show that inequalities and variations still exist? Of course, the answer is that we need to keep producing evidence, not just to understand the causes, “the causes of the causes” and in order to plan the best strategies to tackle these inequalities. Moreover, the evidence needs to be presented in new ways to reach the hearts and minds of policymakers in order to enact change.
In Circulation this week, Ezatti and colleagues consider the effect of macroeconomic changes on cardiovascular risk factors over time at the global level for hypertension, diabetes, hypercholesterolaemia and obesity. At the country level, systolic blood pressure, total cholesterol and body-mass index were positively associated with gross domestic product (GDP) and Western diet in 1980, whereas only total cholesterol remained positively associated with GDP in 2008. In an accompanying editorial, I make the point that existing surveillance systems for cardiovascular disease and its risk factors at global level are inadequate. This week, I am at the American Heart Association Cardiovascular Epidemiology and Prevention Meeting in New Orleans, learning about new data and new ways of presenting the data regarding cardiovascular diseases. Relating changes in cardiovascular disease to economic and macroeconomic change seems a promising strategy to get the attention of policymakers.
South Asians, ethnicity and cardiovascular disease:no easier to unravel than genetics
South Asians (people from India, Pakistan, Bangladesh, Nepal, Maldives and Sri Lanka) seem to have high rates of heart attacks and stroke (collectively known as cardiovascular disease) that is not explained by widely-known risk factors such as high blood pressure or smoking. When you consider that the Indian subcontinent accounts for over 1.4 billion people and carries the greatest global burden of cardiovascular disease, it is important to understand what puts these people at increased risk, even when they migrate to other countries.
I have spent this week at Northwestern University in Chicago, learning about their great programme of clinical research into the causes of cardiovascular disease. I heard of my favourite ever acronym for a study, “MASALA” (The Mediators of Atherosclerosis in South Asians Living in America) which is recruiting 1000 South Asians in Chicago and San Francisco and will compare risk factors and development of heart disease. Interestingly, whereas study of South Asians has been at the forefront of research regarding ethnicity and cardiovascular disease in the UK, study of ethnic disparities in health has tended to focus on African American populations.
It is well-known that risk of stroke and risk of heart disease are linked to socio-economic status. In a London-based study of 1400 South Asian men, deaths from heart attacks and stroke were more likely in men whose fathers had “manual” occupations, or in men who had completed less than 11 years of formal education. This effect was more marked in men who themselves were engaged in manual work, and the authors concluded that “childhood socioeconomic position”, together with adult socioeconomic position cumulatively influenced the risk of dying of from cardiovascular disease. Studies in Scotland have shown similar results. There is definitely a relationship with socioeconomic deprivation and heart disease in Indians living in India How do we best measure “social disadvantage”? Do we need a “social disadvantage index”, as has been proposed by Canadian researchers led by Salim Yusuf? They found that social disadvantage was higher among older people, women, and non-white ethnic groups. The jury is still out regarding the best way to measure socioeconomic status, but it does appear that ethnic minorities, including South Asians, tend to suffer from a greater degree of social deprivation, which may contribute to cardiovascular disease. However, results of the 2010 US census show that Indians living in America have higher income than other ethnic groups and are the fastest growing ethnic minority, so socioeconomic status is not telling the whole story about the high rates of cardiovascular disease in America.
What about migration? The Indian Migrant Study and other studies suggest that South Asians who migrate within their countries from rural to urban areas, as well as those who move to Western countries, seem to have increased risk of heart attack and stroke, and there seem to be roles for socioeconomic status, risk factors and migration itself.
In the UK, one study has shown higher reported “psychosocial adversity” in South Asians who had suffered heart attacks, compared with UK whites, in terms of greater chronic stress, in the form of financial strain, residential crowding, family conflict, social deprivation and discrimination, despite larger social networks. These effects were largely independent of socioeconomic status. Linguistic and cultural barriers have been previously cited as potential causes of higher rates of heart attacks in South Asians, but it is not as simple as that, as Hindus and Sikhs were more likely to seek help for chest pain than their white European counterparts in one study.
Lifestyle is also likely to be very important and many differences seem to manifest in early childhood, such as lower physical activity in South Asians and higher saturated fat intake in Indians.
Last year, I wrote about research looking at ethnicity and risk of stroke in the UK and the USA. As I said then, the research continues to describe differences in traditional and non-traditional risk factors, but not so much has been done to design and implement interventions to reduce the variations in health due to ethnicity. The interplay of environmental factors and ethnicity in cardiovascular disease is no less complex than the interplay of genes and environment. Encouragingly, the discourse about the best policies to tackle health disparities related to ethnicity is well underway on both sides of the pond.
Aspirin and prevention-who knows best?
As the UK descends into hysteria around petrol and pasties, I have been reflecting for the last week on Peter Rothwell’s recent Lancet papers about cancer prevention and the role of aspirin. Basically, daily low-dose aspirin not only prevents development of new cancer, but also the spread of cancer. Aspirin is one of the oldest drugs in the drug cabinet of hospital wards and GP surgeries, but we continue to discover more about its roles in medicine. As new evidence appears on the horizon, the information and guidelines for practising doctors and their patients still continues to change. There are inevitably time delays in how quickly new information filters through healthcare settings and broader society, and how it is interpreted by both the patient and the doctor.
Aspirin has several different uses which are proven by large bodies of evidence, including as a painkiller, prevention of cardiovascular disease in people at risk (primary prevention) and people with known cardiovascular disease (secondary prevention) and now for prevention of cancer. I always love to refer back to the Hippocratic Oath, and so we have to weigh aspirin’s harms with these many benefits. The main harm with aspirin is bleeding, particularly people who have a tendency towards bleeding anyway, e.g. individuals with history of gastric ulcers.
Interestingly, as the new data is emerging about the long-term preventive effects on cancer, the use of aspirin for two other indications is in decline due to evidence of not that much good when weighed against the risk of bleeding. First, most doctors do not recommend low-dose aspirin for primary prevention of cardiovascular disease, largely due to available data from meta-analyses showing that it does not change mortality in diabetics or non-diabetics. Second, in patients with atrial fibrillation, a heart rhythm problem which increases risk of stroke, aspirin is no longer recommended, yet most guidelinesaround the world still include it. So while we can recommend aspirin for long-term cancer prevention, we may not be able to recommend it in healthy individuals for long-term stroke prevention.
Evidence-based medicine is following a moving target of diseases and treatments and so the evidence is also always changing, even for drugs as old as aspirin. So for newer drugs, you can begin to imagine how little we know. The challenge is to keep all people, both doctors and patients up-to-date with all available evidence and guidelines. However, we know that this is difficult, given that both doctors do not always follow guidelines and people do not generally like to take tablets. Notably, most news reports covering the “aspirin and cancer” story advised people to go and see their doctor before starting the drug. Fergus Walsh, of the BBC, quoted a notable academic, “Doctors were good at treating disease, but when it came to preventing ill-health then people had to make their own judgements”. I agree. I wonder whether people have as much chance of making the “right decision” themselves. And before you ask, I do not take an aspirin a day yet, but I did start cycling to work again this week. One preventive step at a time.