Tuesday August 26 2008
The study did not say how much aspirin is needed
“Medical experts have prescribed a daily dose of aspirin for millions of Britons to beat heart disease and strokes”, the Daily Express reported. Extensive media coverage was given to a study in which researchers calculated the ideal age for healthy people to take aspirin to aid circulation and help them live longer. The ages, 48 years for healthy men and 57 years for healthy women, were chosen as these age groups have a one in 10 chance of having cardiovascular disease in the next decade.
This study determined the ages at which risk of developing coronary heart disease (CHD) changes from being low to moderate or high and suggests that these ages could be used as a threshold beyond which aspirin is routinely given to healthy adults to prevent a first CHD event. The British Heart Foundation suggests that more research is needed to justify a ‘blanket prescription’. This study proposes a pragmatic alternative to complex calculations of individual risk that are currently used. In future, controlled studies may be used to test its application at a population level. Anyone considering taking regular doses of aspirin should speak to their GP first.
Where did the story come from?
Dr Uditha Bulugahapitiya and colleagues from the University of Sheffield and the University of Nottingham carried out this study. Sources of funding were not mentioned. The study was published in the peer-reviewed medical journal: Heart.
What kind of scientific study was this?
In this cross sectional study, the researchers set out to establish the appropriate age to prescribe aspirin for the purpose of preventing cardiovascular disease in men and women without diabetes. The American Heart Association recommends that people with an annual CHD risk of greater than 1% should be given aspirin (because this level of risk offsets the potential increase in risk of gastrointestinal bleeding). The researchers say that there may be a large number of eligible patients not receiving treatment and several groups are advocating a more ‘pragmatic approach to aspirin prophylaxis based on age threshold alone’. In light of this, the researchers determined an age cut-off for aspirin prophylaxis in patients without diabetes which took into account their CHD risk.
The researchers used anonymous data on people from 304 general practices in England and Wales. The dataset was obtained from The Health Improvement Network [THIN], which is known to be a robust and valid dataset. From this, the researchers identified 989,434 patients aged between 30 and 74 years without diabetes who had not been taking any lipid lowering drug therapy and had no history of arterial disease. A random sample of 12,000 patients was selected, and of these, 11,232 patients had complete datasets. The records (biochemical and demographic details) that were used were those available on December 31 2005. All patients had to have been registered at their practices for the entire preceding 12 months.
Researchers used the JBS risk calculator (derived from the Framingham risk algorithm) to calculate the CHD risk; this is based on factors such as age, sex, systolic and diastolic blood pressure, smoking status, diabetes status, and total and HDL cholesterol. They then used complex mathematical techniques to estimate the relationship between age and CHD risk. Using these methods they were able to establish at what age their sample (men and women without diabetes) moved from low risk (a 10 year CHD risk of <10%) to moderate or high risk (a 10 year CHD risk of >10%). These risk thresholds were selected on the basis of recommendations from the American Heart Association that benefit of aspirin therapy outweighs the risk of gastrointestinal bleeding.
What were the results of the study?
The researchers found that the average 10 year CHD risk in the population was 9.0% (11% for men and 7% for women). Risk increased with age and the transition from low to moderate or high risk occurred at 47.8 years for men and 57.3 years for women. When the researchers repeated their calculations using a different risk threshold between low and moderate or high risk (i.e. 15%), they found that the transition occurred in men at ages 55.8 years and in women at 68.1 years.
What interpretations did the researchers draw from these results?
The researchers suggest that based on these results, prophylactic aspirin should be considered routinely for all healthy (non-diabetic, no history of arterial disease) men above the ages of 48 years and for women over 57 years. They say that the risk of adverse events associated with aspirin (for example gastrointestinal bleeding) may outweigh benefits if given to patients below these age cut-offs. For patients below the ages of 30 years or over 75 years, the decision to initiate aspirin therapy should be based on an assessment of the individual’s risk.
What does the NHS Knowledge Service make of this study?
This cross-sectional study presents practitioners with an alternative aid in helping them to decide who to prescribe aspirin to in order to prevent cardiovascular disease. Its results suggest that an age threshold alone may be a practical way to guide aspirin prescription. Current international guidelines recommend that the decision is based on a calculation of the individual patient’s risk, but the researchers acknowledge that there is limited uptake of this practice.
Some of the results of this study – i.e. that women over 57 switch from being ‘low risk’ to ‘moderate/high risk’ are in contrast to results from other studies which suggest that aspirin has maximum benefit in women aged over 65 and not in the age groups below (45-54 years and 55-64 years).
The researchers highlight further limitations of their research, and say that:
- Their results are based on data collected when patients visited their GP. This population may not therefore represent all ‘healthy community subjects’.
- As they relied on records to determine whether a patient had diabetes or pre-existing CHD (to exclude them from the study), it is possible that some patients had undiagnosed diabetes or undiagnosed CHD.
- They had to assume that the JBS risk calculator that they used is an accurate tool.
The researchers acknowledge that simply using age as a threshold to guide aspirin prescription may mean that some low-risk individuals are treated and some high-risk ones are not. They also highlight that the ‘final decision about the use of aspirin must eventually be made after discussion with a health care provider, so that a balance between benefit and risk for an individual patient can be ascertained’. Given that the risks associated with the use of aspirin may outweigh the benefits in a young, healthy population, the thresholds for younger people are less clear. The same applies for older people (over 75 years) and people with diabetes.
More research will be needed to determine whether a ‘blanket prescription’ of aspirin could be recommended for particular ages at a population level. Given the potential risks associated with regularly taking aspirin, anyone, regardless of how healthy they think they are, should speak to their GP first.