Scientists have helped unravel the link between higher levels of education and reduced risk of heart attack and stroke.
Previous research showed every 3.6 years spent in education can reduce a person's risk of heart disease by a third.
However, scientists did not know exactly why spending more time in education reduced a person's risk of cardiovascular disease (a general term for any condition affecting the heart or blood vessels, including heart disease, heart attack and strokes).
In the latest study, led by Imperial College London, University of Bristol, University of Cambridge and University of Oxford, scientists used statistical and genetic analyses to show only 40 per cent of the effect of education on cardiovascular disease risk is explained through body mass index (a measure of body fat based on height and weight), blood pressure or how much a person has smoked.
Analysis in the study also suggested each 3.6 additional years in education was linked to a reduction in BMI of 1kg/m2, and a reduction in systolic blood pressure of 3mm/Hg. A BMI between 18.5 and 24.9 is generally considered healthy, while systolic blood pressure should be between 90 and 120.
Dr Dipender Gill, co-first author of the work from Imperial's School of Public Health, said: "Although we know from previous research that someone who spends more time in education has a lower risk of heart disease and stroke, we didn't know why. Surprisingly, our research suggests only half of this protective effect comes from lower weight, blood pressure and less time smoking. We now need to investigate what other reasons may link education and lower cardiovascular disease risk. One possibility is that people who spend more time in education tend to engage more with healthcare services, and see their doctor sooner with any health complaints."
Alice Carter, co-first author from the University of Bristol explained: "Past policies that increase the duration of compulsory education have improved health and such endeavours must continue. However, intervening on education is difficult to achieve and requires large amounts of both societal and political change. Our work shows that there are opportunities to intervene, after education is completed, to reduce the potential risk of heart disease. By lowering BMI, blood pressure or rates of smoking in individuals who left school at an earlier age, we could reduce their overall risk of heart disease. However, it is important to note this work looks at the effect of education on a population level risk of heart disease - and leaving school earlier does not necessarily mean an individual will go on to develop heart disease."
In the research, published in The BMJ, the scientists used two types of analysis to investigate the link between education and cardiovascular risk.
In the first approach, they analysed data from over 200,000 people in the UK, and compared the number of years individuals spent in education with their body mass index (BMI), blood pressure, the lifetime amount they have smoked, and consequent cardiovascular disease events such as heart attack or stroke.
In the second approach, the research team used a type of analysis called Mendelian randomisation. Using genetic data from public databases, the team searched through data from more than one million people to investigate the link between education and cardiovascular disease risk. They focused on points in the genome where a single 'letter' difference in the DNA - called a single nucleotide polymorphism (SNP) - has been linked to years in schooling.
The research team, who were funded by the Medical Research Council and Wellcome Trust, then assessed the link between these genetic markers for years in schooling with genetic markers for BMI, blood pressure and lifetime smoking (the researchers only assessed years in education and did not analyse intelligence in any way).
Using these two methods, they found that body mass index, blood pressure and smoking contribute to the effect of education, explaining up to 18 per cent, 27 per cent and 34 per cent respectively. Combined, these factors accounted for 40 per cent of the effect of education on cardiovascular risk.
Dr Gill said this total is less than would be expected by simply adding the individual percentages for BMI, blood pressure and smoking. This suggests the effect of the three factors have some overlap.
He added that most of the data analysed was from individuals of European heritage, and more work is now needed to investigate the link between education and cardiovascular risk in other ethnic groups.