Thursday April 7 2016
Fresh fruit is a rich source of antioxidants
"Daily fresh fruit lowers heart death risk as much as statins," The Daily Telegraph reports.
A study of over a half a million Chinese people found that a diet rich in fresh fruit was linked to a reduced risk of cardiovascular diseases.
But don't ditch the statins in favour of an "apple a day", if they have been recommended for you.
The study looked at people without cardiovascular disease, and did not compare fruit to statins.
Statins are prescribed for people with cardiovascular disease, or a raised chance of getting it, and fruit is not a suitable alternative to medication. The study was also carried out in a country with different lifestyles to the UK. Finally, the study did not prove that fruit caused the lower death rate in people who ate it regularly.
The effect of fresh fruit that the study found was much bigger than the effects found in previous research in Western countries. People who ate fruit every day were likely to be richer and better educated, which itself could have affected their chances of dying of cardiovascular disease (although the researchers did try to account for this).
The study adds to evidence that people who eat fruit daily tend to be healthier, but it does not mean that fruit can be used instead of medication for people with cardiovascular disease.
Fresh fruit should be seen as an addition to statin treatment, not an alternative.
Where did the story come from?
The study was carried out by researchers from the University of Oxford, Peking University, the Chinese Academy of Medical Sciences, the Chinese National Center for Food Safety Risk Assessment, and three regional Chinese centres for disease control.
It was funded by the Wellcome Trust, the Kadoorie Charitable Foundation and the Chinese National Natural Science Foundation. The study was published in the peer-reviewed New England Journal of Medicine.
The Telegraph's reporting unhelpfully mixed information about the effect of statins in with the report of the Chinese study. It is unclear why the newspaper did this, as the Chinese study did not look at statins at all.
Although the report admitted that the researchers "do not recommend swapping statins for fruit", it may give some people the impression that statins and fruit are equally effective.
The Mail Online's reporting was clearer, as its headline mentioned that the study was in China, and results may be specific to that country.
The Daily Express' reporting was also accurate and contained an interesting quote from one of the lead researchers, who said: "We still don't know exactly what it is about fruit that appears to reduce heart attack and stroke risk."
What kind of research was this?
This was a large prospective cohort study, which recruited half a million volunteers in China to measure diet, health and deaths from disease. Researchers wanted to see whether the link between fruit consumption and cardiovascular disease seen in previous Western studies also applied in China. Cohort studies are good at picking out patterns of associations, but they can't prove that one thing (in this case, fruit consumption) is a cause of another (death from cardiovascular disease).
What did the research involve?
Researchers questioned around half a million Chinese adults about their health and diet, and took measurements including their body mass index (BMI) and blood pressure. They followed them up for seven years. After adjusting their figures to take account of confounding factors, they looked to see whether people who regularly ate fruit were less likely to have died from cardiovascular disease, or had a heart attack or stroke.
The study recruited 512,891 adults aged 35 to 74, living in different locations across China from 2004 to 2008. People underwent a battery of tests and questions; researchers recorded information about their weight, height, blood pressure, glucose level, whether they smoked or drank alcohol, their income and education level, and their diet. They filled in a food questionnaire asking how frequently they consumed food from 12 major groups, including fresh fruit and vegetables.
The researchers followed up on 451,665 people who didn't have cardiovascular disease at the start of the study, and who weren't taking any medicine to lower blood pressure. They checked whether they were still alive, and whether they'd been treated for a major coronary event such as a heart attack, and whether they'd had either an ischaemic or haemorrhagic stroke. An ischaemic stroke is when a blood clot blocks a blood vessel in the brain. A haemorrhagic stroke is when a blood vessel ruptures, causing bleeding in the brain. The latter type of stroke is more common in China than in Western countries.
Researchers ran a number of analyses on the data to try to account for factors that are known to affect the risk of heart attack and stroke (confounders) such as age, sex and smoking. They calculated the chances of having any of the major outcomes for people who ate fruit never or rarely, compared to people who ate it at least daily. They used that to estimate how many deaths might be attributed to people not eating fruit, assuming that fruit was the cause of the lower risk of death.
What were the basic results?
Only 18% of people in the study ate fresh fruit daily. Compared to people who rarely or never ate fresh fruit, daily fruit eaters were 40% less likely to have died of cardiovascular disease (hazard ratio [HR] 0.60, 95% confidence interval [CI] 0.54 to 0.67). They were also 34% less likely to have had a heart attack (HR 0.66, 95% CI 0.58 to 0.75), 25% less likely to have had an ischaemic stroke (HR 0.75, 95% CI 0.72 to 0.79) and 36% less likely to have had a haemorrhagic stroke (HR 0.64, 95% CI 0.56 to 0.74).
The study also showed that people who ate fresh fruit daily had lower blood pressure and blood glucose levels at the beginning of the study, although interestingly these did not explain the differences in deaths, heart attacks and strokes. Fruit eaters were also likely to be younger, female, from urban areas, better educated, with a higher income and less likely to smoke or drink alcohol.
Assuming that fruit is the reason for the lower risk of cardiovascular death among daily fruit eaters, the researchers say, 16% of deaths from cardiovascular disease could be avoided – a whopping 560,000 deaths a year in China – if everyone ate fresh fruit daily.
How did the researchers interpret the results?
The researchers said: "it is difficult to establish causality reliably in observational studies of dietary factors that have such moderate relative risks and potential for confounding." In other words, they can't be sure the "moderate" differences in risk they found were down to fruit alone, and not to other factors. They say that, in particular, "residual confounding by socioeconomic status is still possible," despite their attempts to adjust figures to take account of this.
However, they say, given the healthy properties of fruit, it is plausible that it could be the cause of the lower death and disease rates seen among Chinese people who eat fruit daily.
They suggest that the weaker association between fruit consumption and cardiovascular death seen in previous studies, which have mainly been carried out in Western countries, can be explained partly because daily fruit eating is rare in China. They say this could mean that only a little fruit is needed, whereas previous studies have looked at the effect of each additional piece of fruit, in a population where daily fruit consumption is common.
The study adds to evidence that fresh fruit is likely to be good for our cardiovascular health, although we can't be sure from this study that it definitely prevents deaths, heart attacks or strokes. Observational studies cannot prove that one factor causes another, even when they are as big as this study, because other unmeasured factors could be responsible for the results. In this case, a major potential confounder that the researchers failed to take into account was whether the participants were taking any medication – they only excluded people taking blood pressure tablets.
The link with statins, made by the Telegraph, is unhelpful, confusing and unnecessary. While statins have been shown to reduce the risk of heart attacks and strokes by about the same figure – approximately one third, depending on the study – the statin studies were randomised controlled trials, which can show a causal relationship. In addition, they were carried out in Western populations with cardiovascular disease, or at risk of cardiovascular disease. These studies had little in common with this mass observational study of diet in healthy Chinese people.
However, we do know that fruit is likely to be a healthy part of a balanced diet. It's important to note that people in the study were asked about whether they ate fruit, not whether they drank fruit juice. Fruit juice often contains a lot of sugar, and misses out on the fibre found in fresh fruit. Whole fruit is likely to be healthier.
It’s also worth noting that the researchers couldn’t check for an effect of eating fresh vegetables daily, because almost everyone in China eats vegetables every day. The UK dietary recommendations are to eat five portions of fruit and vegetables a day. This research backs the idea that eating fruit regularly as part of a balanced diet is good for your heart and circulation health.
If you have been prescribed statins, then you should not stop taking them without first consulting your doctor. Adding a daily portion of fresh fruit to your diet could help to increase their effectiveness, but should not be regarded as a suitable alternative to statin treatment.