Wednesday October 12 2011
Lifestyle factors such as diet influence a person’s risk of developing CVD
The Daily Express reports that a “wonder diet cures heart disease” and goes on to say that “a simple diet packed with fruit and raw vegetables is the key to beating heart disease.”
The news report is based on a large study that looked at how certain genetic variations known to increase a person’s risk of heart attack and cardiovascular disease (CVD) are influenced by lifestyle factors, such as diet, physical activity levels and smoking.
The study found that some of the effects of these genetic variations could be countered by a diet high in raw vegetables, fruits and berries. Raw vegetables seemed to have particularly important effects. The researchers found similar effects when looking at the risk of CVD and diet in a different group.
This well conducted study's findings indicate that people with specific genetic risk factors for heart attack can reduce their risk through a diet high in fresh fruit and vegetables. It does have some limitations in that it relied on people accurately recalling their food intake and assessed only one area of genetic variation. Despite these however, the findings appear to be robust. As about 50% of the ethnic groups tested in this study carried one of the four risk variants, the application of these findings to the general population is likely to be high.
Where did the story come from?
The research was led by researchers from McGill University in Canada in collaboration with a number of researchers from other universities around the world. It was funded by a grant from the Heart and Stroke Foundation of Ontario and other grants associated with the collaborating researchers.
The study was published in the peer-reviewed medical journal Public Library of Science (PLoS) Medicine.
Generally, this study was reported accurately in the media although some headlines may have exaggerated the significance of these findings. For instance, the Daily Express’ headline says, ‘Wonder diet cures heart disease’. However, although the study found this diet to be of benefit for heart disease, the findings do not signify a cure.
What kind of research was this?
This study investigated how diet could influence a person’s risk of heart attack and CVD when they possessed particular genetic variations that increased their risk.
This was a gene-environment association study using participants enrolled in the INTERHEART study, a global retrospective case-control study that investigated potential risk factors for heart attack.
Cardiovascular diseases (CVDs) affect the heart and blood vessels and are a leading cause of illness and death in most developed countries. Lifestyle factors such as diet, exercise and smoking, as well as genetic factors, influence a person’s risk of developing CVD. Recent studies have identified several genetic variations that are associated with an increased risk of CVD. One of these areas is in a region of the chromosome (the structure DNA is packed into in each cell) called 9p21.
This study looked at how environmental factors were linked to variations in the 9p21 region and how the interaction of these influenced a person’s risk of heart attack and CVD.
What did the research involve?
The researchers assessed four different genetic variations (called single nucleotide polymorphisms SNPs) within the 9p21 chromosome region of DNA. They compared the genetic information of 3,820 participants who had had a non-fatal heart attack, with that of 4,294 healthy controls. All the participants were enrolled in the INTERHEART study and were from five ethnicities: Europeans, South Asians, Chinese, Latin Americans and Arabs. This made up 27% of the total people enrolled in the INTERHEART study.
The main analysis of the INTERHEART data was in two parts. In the first part, the researchers looked at the effect of the four SNPs on the risk of heart attack. In the second, they looked at how this risk was influenced by environmental factors such as smoking, activity level and diet.
Diet was assessed by a short food frequency questionnaire of 19 food items. These were then grouped into three dietary categories the researchers called oriental (soy sauce, tofu, pickled foods, green leafy vegetables, eggs and low sugar), western (eggs, meats, fried and salty foods, sugar, nuts and desserts), and prudent (raw vegetables, fruits, green leafy vegetables, nuts, desserts and dairy products). For the prudent diet, fresh vegetables, fruits and berries made up the largest components of the score.
The researchers aimed to validate their findings from the INTERHEART study in a large group of people that were enrolled in a different study that looked at CVD. This second group were enrolled in a prospective study, called the FINRISK study, containing information on 19,129 Finnish individuals, in which there were 1,014 cases of CVD. The analysis of the FINRISK participants used different methods to assess participants diet than the INTERHEART study.
The statistical analysis was appropriate for this type of study.
What were the basic results?
- All four specific variations of the SNPs that were tested increased the risk of heart attack by about a fifth compared to other variations of the SNP (odds ratios ranged from 1.18 to 1.20 for all individuals from all ethnicities combined).The amount that the risk increased for each of the SNPs was affected by ethnicity with South Asians at the highest risk.
- An individual’s risk of heart attack was affected by whether or not they had a prudent diet pattern and which variant of the SNP they had. For example, those that carried a specific SNP variant called rs2383206, and who ate a diet poor in fruit and vegetables, had a higher risk of heart attack than those without the variant. However, carriers of rs2383206 who ate a prudent diet, had the same heart attack risk as those without the risk variant.
- The influence of the prudent diet diminished when the researchers removed the influence of raw vegetable intake. This did not occur when other elements of the prudent diet were removed. This suggested raw vegetable intake is a key component of the influence.
- The more key components of a prudent diet that SNP risk carriers ate, the lower their risk of heart attack compared to those who ate less of this diet.
- The effect of the SNPs on the risk of heart attack was not influenced by physical activity level or smoking.
- Similar dietary interactions were seen to influence the risk of CVD in the FINRISK study.
How did the researchers interpret the results?
The authors say they have demonstrated that different variants of 9p21 SNPs have a consistent effect on the risk of heart attack and CVD in people whose diet has only a low ‘prudent diet score’. The risk diminished the higher an individual’s prudent diet score was.
They say that although it is now known exactly how this association works, they believe that their ‘results support the public health recommendation to consume more than five servings of fruits or vegetables as a way to promote good health.’
This large gene-environment association study provides new insight into the influence of diet on mitigating the increased risk of heart attack associated with specific variations in the 9p21 chromosome region.
The study has some limitations, the main being that the data from the two populations studied (INTERHEART and FINRISK) was collected and analysed in different ways. INTERHEART looked at the effect on the risk of heart attack, while FINRISK looked at the risk of CVD.
The SNPs were analysed differently. The cardiovascular outcomes were made using different criteria (heart attack versus CVD) and there were differences in how the diets were measured. As such, it is not possible to be sure a prudent diet has the same effect on the risk of heart attack as it does on the risk of CVD. Further studies focusing on the specific elements of diet and their influence of CVD would be needed to confirm this.
In addition, the results were dependent on the participants completing the food frequency questionnaires themselves. All dietary studies that use questionnaires are limited by the participants’ ability to recall the food they have eaten accurately. Although these researchers used careful methods to try and eliminate this bias, it is still possible that some inaccuracy was introduced.
There are likely to be many genetic variations and environmental factors that determine an individual’s risk of having a heart attack or developing other CVDs. This study looked at just one area of genetic variation and, while this is an important finding, there will be many others that also contribute to an individual’s overall risk. It is not known whether diet would affect these other areas of genetic variation in the same way as demonstrated in this study.
While these findings have some limitations, and ideally would be confirmed in further studies, they do correspond with what is already known about eating a healthy, balanced diet containing fruit and vegetables in order to promote good health.
Overall, this was a good study that showed people with specific genetic risk factors for heart attack may reduce their risk through a diet high in fresh fruit and vegetables to that similar to someone without the genetic risk factors. In this study, about 50% of the ethnic groups tested carried one of the four risk variants, and so the application of this study to the general population is likely to be high.
This research supports the well-established recommendations to consume more than five servings of fruits or vegetables as a way to promote good health.