A few days ago, I read this article on Medpage: Berries Ward Off MI in Women.
At first glance I thought, “Score! I have blueberries almost every day- I am going to be heart-attack free!”
Then I realized this is a great article to share on the blog- not only does it fit in with my mission of helping others learn about health (and helping myself learn about health too) but it’s a great article to demonstrate some things to look for when reading scientific literature. We have classes in medical school aimed at teaching us how to skeptically read articles, how to look for mis-representation of data, and how to ask questions about the research. I have to admit that I am the queen of skepticism. I don’t think there is ever one good answer to a question- generally I believe that lots of different factors go into something that is discovered scientifically.
Take for instance the ‘Paleo’ trend. I’ve read tons of articles (some citing good quality scientific research) about the benefit of reducing grains in one’s diet. On the complete opposite side of the diet spectrum, I’ve read the China study and the papers detailing the reduction of cancer markers when animal protein is removed from the diet. These two ‘diets’ are advocating completely different things. They both have scientific studies backing them. Who is to say which one is right? A better question… who cares??
I have accepted that there will probably be no be-all-end-all method when it comes to healthy living. I continue to subscribe to the belief that everything in moderation is the way to go. If you’re eating a perfectly vegan diet but you’re miserable, who’s to say that misery won’t cause health problems? If you have a cupcake every once and a while and you’re joyful and fulfilled, who’s to say that joy won’t override the inflammation and chemical-evilness of the cupcake?
Anyway, I digress. My point is that if you’re going to read an article, I personally believe you should be a skeptic. You should take the points that will inspire you to make healthy choices and stay happy.
I’m going to go through the following article and point out some good quality research markers and point out some bad stuff too. I hope this helps you learn a few things to look out for the next time someone tells you about their product that is backed by scientific research and proves you will lose 35lbs in 2 weeks and live 10 years longer!
Here we go! (My additions will be in pink )
Berries Ward Off MI in Women
MI stands for myocardial infarction which is the fancy-schmancy term for heart attack.
Young and middle-age women whose diet included high levels of anthocyanins — the flavonoids present in red and blue fruits such as strawberries and blueberries — had a significantly reduced risk for myocardial infarction (MI), a large prospective study found.
‘Significantly’ is a HUGE buzz-word. It means that the research was statistically significant (more on that later). If you read an article that says something is significant, but the p value is greater than 0.05, it’s NOT significant.
Women whose anthocyanin intake was in the highest quintile had a 32% decrease in risk of MI during 18 years of follow-up (HR 0.68, 95% CI 0.49 to 0.96, P=0.03), according to Eric B. Rimm, ScD, of Harvard University, and colleagues.
All those numbers in parenthesis are important. The HR is the hazard ratio. It means the likelihood that something increases your risk of something else. For example, the hazard ratio of smoking cigarettes in association with lung cancer is something around 2 or 3; that means if you smoke, you are 2 or 3 times more likely to get lung cancer. A Hazard Ratio less than 1 means that something decreases your risk of something else. So in this case, the Hazard Ratio of 0.68 or 68% means you are only 68% as likely to have a heart attack (aka a 32% decrease in risk).
CI means confidence interval. All you need to know about this is that the interval should never cross the number 1. In this study, the interval is between 0.49 and 0.96 which doesn’t cross 1 so that’s good. If it was 0.49-1.11 that would cross 1 and mean that the data isn’t as good. If it was 20.15-25.6 that doesn’t cross the number 1 and is still okay. Make sense?
Lastly, the p value is the percentage that something could have happened by chance. Say you flipped a quarter and 8 out of 10 times it landed heads. What is the likelihood that that simply happened by chance vs. the likelihood there is something weird going on with your quarter? A p value of 0.05 (or 5%) means that there is a 95% chance your result wasn’t from chance alone. In a study, you want your P value to be below 0.05 because you want there to be more than a 95% chance that there is something going on other than dumb luck.
And in a food-based analysis, women who consumed more than three servings of strawberries or blueberries each week showed a trend towards a lower MI risk, with a 34% decrease (HR 0.66, 95% CI 0.40 to 1.08, P=0.09) compared with women who rarely included these fruits in their diet, the researchers reported online in Circulation.
In this part of the study the CI crosses 1 and the p value is greater than 0.05. That means that this part of the study is NOT statistically significant.
“Growing evidence supports the beneficial effects of dietary flavonoids on endothelial function and blood pressure, suggesting that flavonoids might be more likely than other dietary factors to lower the risk of [coronary heart disease] in predominantly young women,” they observed.
They mention ‘endothelial function’. Endothelial cells are the cells that line your blood vessels. They can be damaged by high blood pressure, high cholesterol or triglycerides, plaque formation, inflammation, etc. Things that help these cells repair and function properly help to prevent plaque build-up and clogged arteries. If plaque builds up on your arteries and stops blood flow, or if a plaque rips off like a scab and new clots form, you can have a heart attack. That’s why we care about endothelial cells.
A number of preclinical experiments have demonstrated cardioprotective effects of anthocyanins, including anti-inflammatory effects, plaque stabilization, and inhibition of the expression of growth factors.
While studies have suggested that MI risk is increased in young and middle-age women who smoke or use oral contraceptives (both of which affect your endothelial cells), little is known about the influence of diet in this population, whose risk may differ from that in older women.
The younger women may have a greater likelihood of endothelial dysfunction and coronary vasospasm and less obstructive disease.
Because dietary flavonoids — found in vegetables, fruits, wine, and tea — are recognized as benefiting endothelial function, the researchers looked at outcomes for 93,600 women enrolled in the Nurses’ Health Study II who reported their consumption of various foods and their lifestyle factors every 4 years.
At the time of enrollment, beginning in 1991, participants were ages 25 to 42.
During almost 2 decades of follow-up, there were 405 cases of MI, occurring at a median age of 48.9 years.
Review of the food frequency and lifestyle questionnaires revealed that women who consumed high levels of anthocyanins were less likely to smoke, were more physically active, and had lower fat and higher fiber intake.
****THIS IS SUPER IMPORTANT. When you’re reading an article and trying to be skeptical, try to think of other associated things that could influence the results they found. In this case, the article flat out tells you- people who eat blueberries work out more, smoke less, and eat healthier diets. Maybe they have higher incomes on average. Maybe they were younger in general… these are all things to think about. If you realize that the people who eat berries also make lots of other good health choices, the results of the study aren’t that astounding. Of course these people have less heart attacks! They smoke less and work out more! Duh!
The 32% reduction in MI risk was seen after adjustment for multiple factors including body mass index, physical activity, saturated fat intake, use of caffeine and alcohol, and family history of MI.
Boom! Now you can give the study some credit- they adjusted for the other factors that could have influenced the results including working out, weight, drinking, etc.
“This inverse association was independent of established dietary and nondietary [cardiovascular disease] risk,” the researchers noted.
Even adding conditions such as hypertension, dyslipidemia, and diabetes to the analytical model did not significantly change the risk estimate (HR 0.70, 95% CI 0.50 to 0.97).
Even when they took all the other factors into consideration, eating berries STILL made a difference. Good to know!
Comparison of risk among women in the highest and lowest 10% of anthocyanin intake showed a relative risk of 0.53 (95% CI 0.33 to 0.86) for the high-intake group, which suggested the presence of a dose-response relationship.
Check out the data with what you just learned: The confidence interval doesn’t cross 1 so we’re good to go. The relative risk of 0.53 means that when you compare the people who eat the least amount of berries and the people who eat the most, the ones who eat more have almost 50% less risk of heart attack.
Intake of other types of flavonoids did not significantly lower the risk of MI. The researchers had hypothesized that high intake of flavan-3-ol also would be important, because they had previously identified cardiovascular benefits for one type of flavan-3-ol compound in a meta-analysis.
The lack of effect in the current analysis may have reflected the fact that in the early 1990s, when the study began, most food frequency questionnaires did not include dark chocolate, which is a primary source for flavan-3-ol, they noted.
Adjustment for additional dietary factors such as total fruit and vegetable consumption also did not alter the risk, which suggests “that the benefits are specific to a food constituent in anthocyanin-rich foods (including blueberries, strawberries, eggplants, blackberries, blackcurrants) and not necessarily to nonspecific benefits among participants who consume high intakes of fruits and vegetables.”
However, the results of this study do not support the use of flavonoid dietary supplements, according to Michael Rinaldi, MD, of the Carolinas HealthCare System’s Sanger Heart and Vascular Institute in Charlotte, N.C.
Another super important point because no doubt, some vitamin company will cite this article as a reason why you should buy their concentrated mulberry pills.
The study does suggest that a healthy diet that includes fruits and vegetables can be healthy, said Rinaldi, who was not involved in the study.
“A healthy diet that includes fruits and vegetables can be healthy”… that makes sense….?
“On the other hand, if you’re going to say that these flavonoid substances in the berries should be taken as supplements, that’s not what the study has the power to say,” he told MedPage Today in an interview.
Limitations of the study included a lack of information about the results of cardiac catheterization and the possibility of additional unmeasured confounding factors.
Quality studies should always list problems with the study.
In addition, while the model adjusted for intake of a number of other potentially beneficial food components, there may have been other unidentified compounds in fruits that contribute to cardioprotection.
“In a population-based study like ours, it is impossible to disentangle the relative influence of all the constituents of fruits and vegetables,” the researchers wrote.
Further research will be needed to identify cardiac biomarkers that could help explain mechanisms of action, to explore dose responses, and to evaluate longer-term clinical endpoints.