A diet based on fruit and vegetables and “the odd glass of wine” cuts the risk of heart attack by more than half, reported the Daily Mail on October 24 2007. Women “who ate lots of fruit and vegetables in conjunction with wholegrain foods, fish, beans and small amounts of alcohol were 57 per cent less likely to have a heart attack”, the newspaper said.
The story is based on a six-year study in postmenopausal women which looked to see whether a pattern of several healthy lifestyle behaviours had any impact on the incidence of coronary heart disease and mortality. The study is well-conducted and offers more evidence that a healthy diet, particularly when combined with a healthy lifestyle, can reduce the risk of heart attack.
Where did the story come from?
Dr Agneta Åkesson and colleagues from the Institute of Environmental Medicine at the Karolinska Institute in Stockholm, Sweden and from the Department of Pediatrics at Boston University School of Medicine in Massachusetts carried out this research. The study was funded by research grants from the Karolinska Institute, the Swedish Research Council and the Swedish Council for Working Life and Social Research. It was published in the peer-reviewed medical journal Archives of Internal Medicine .
What kind of scientific study was this?
The study is a prospective cohort study in women who were originally included in a larger study in the 1980s called the Swedish Mammography Cohort. In 1997, women from the original study who were still alive were sent a questionnaire asking about their diet and lifestyle. The 24,444 women who responded were then included in this study. The researchers did not include women who had ischaemic heart disease, cardiovascular disease or cancer (who they identified by looking at their records in hospital and cancer registers). Nor did they include women who said that they had diabetes mellitus. Others were excluded if they did not answer enough questions on the questionnaire.
The researchers monitored these women for six years using various records, including the Swedish Hospital Discharge Registry and the Cause of Death Registry, to see if any of them experienced non-fatal or fatal myocardial infarction (heart attack). They identified five different dietary patterns “healthy” (vegetables, fruit and legumes), “alcohol”, “sweets”, and “Western/Swedish” (red meat, processed meat, poultry, rice, pasta, eggs, fried potatoes, fish). They analysed what effect being in these particular dietary categories had on women’s risk of a heart attack during the six years of follow up. They also assessed what effects a low-risk lifestyle (non-smoking, low levels of abdominal fat, high levels of physical activity) had on the risk of heart attack within these dietary categories.
What were the results of the study?
The researchers found that during follow up there were 308 heart attacks of which 51 were fatal. They found that a combination of "low-risk diet” (i.e. people who a good diet high in vegetables, fruits, legumes, fibre, vitamins, polyunsaturated fats etc.) and moderate alcohol intake (at least 500ml of alcohol per day) was associated with a 57% reduction in risk of heart attack compared with those women who have a less healthy diet and low alcohol intake. They found that other factors, including having a low waist-to-hip ratio (i.e. less than 0.85) and not being a current smoker also reduced the risk of heart attack by about 30% and 60% respectively.
When the low-risk diet and moderate alcohol intake was also combined with low-risk lifestyle factors including not smoking, avoiding being overweight and taking physical exercise, the risk of heart attack was reduced by 92% compared to women who had a high-risk diet and high-risk lifestyle.
What interpretations did the researchers draw from these results?
The researchers conclude that consuming a lot of vegetables, fruits, whole grains, fish, and legumes and taking in a moderate amount of alcohol reduces the risk of heart attack in women. They say that combining all the benefits from a good diet, high activity levels and healthy body weight could prevent three out of four heart attacks in their current population.
What does the NHS Knowledge Service make of this study?
This is a well-conducted study in a large number of women. The prospective design – asking healthy women about their diet and then monitoring them until there was an outcome (i.e. they had a heart attack) – is a strength of the study. This means there are no concerns that women who had a heart attack may have reported their eating differently to those who didn’t or that if asked about past events, the women could have forgotten what they ate. The limitations of the study are few and the researchers highlight them:
- They say that it is inevitable that there are some errors in the way women reported their diets. However, due to the prospective design, this would have affected all women equally so would not have a differential effect on the results.
- As the researchers point out, there were only very few heart attacks in the low risk group (they don’t report how many) and that this may mean that some of their estimates are “imprecise”.
- There weren’t many cases of fatal heart attacks (51 women died from a heart attack during follow up), so they were unable to determine whether a healthy diet or low risk lifestyle has any effect on mortality.
- Because quite a few women were excluded from the analysis for not providing enough information about their food consumption, the results may not apply to all populations.
- Similarly, as the study was only conducted in postmenopausal women, the findings may not apply in preventing heart attacks in younger women and in men. It seems sensible to extrapolate the results to them, but further research is needed to confirm this.
The findings from this study contradict those from some previous studies and confirm the results of others, indicating what a complex area of research this is. Although well conducted randomised controlled trials would be the best way to answer the remaining questions once and for all, as the researchers point out, ”long-term [studies of this kind] are difficult to perform for multiple risk factors”.
For now, behaviours that are known to reduce heart disease, such as healthy eating, moderate exercise and stopping smoking, should be recommended.
Sir Muir Gray adds...
I would not call this news; the headline should have been “Yet more good news about six a day – five fruit and veg and a glass of wine, and by the way, don’t forget to take an extra 3000 steps a day”, but I suppose that would be too long for the editor to accept!