Sep. 16, 2012 at 11:11 AM ET
By Cassie Shortsleeve
Is there danger boiling in your blood? If you're buying into recent headlines, that's probably what you're thinking. According to a recent Harvard University study, having a particular blood type increases your risk of coronary heart disease.
The gist: After analyzing results from two large observational studies--the Nurses' Health Study and the Health Professionals Study, including almost 90,000 people--researchers concluded that people with the blood type AB had a 23 percent increased risk for heart disease when compared to people with type O. People with type B also had an 11 percent increased risk, while those with type A saw their risk shoot up by 5 percent.
But don't bang down your doctor's door just yet. The research is flawed, says Eric Topol, M.D., Men's Health cardiology advisor and genetics professor at the Scripps Research Institute in San Diego.
Basically, that 23 percent you've seen in headlines isn't exact because of the small amount of people with type AB blood--statistically, it could be much lower or even higher, Dr. Topol says.
"Making statistical adjustments can lead to wrong conclusions." Blood type AB is extremely rare, and there is inadequate statistical power when you're talking about such a small amount of people, Dr. Topol says.
Researchers pooled numbers from data that wasn't specifically about blood type and heart disease risk. And while people were asked to report blood type in some of the studies used in the meta-analysis, the original studies were not intended for this purpose. "It's a weak way to look at the question," says Dr. Topol. (Which leads us to wonder: Should You Believe All Medical Studies?).
The better way to look at the results would be type O (a more common blood type) versus the rest of the blood types--this way, you have enough people to look at. Then there's just under a 10 percent increased risk in almost 90,000 people. Not to mention that there are hundreds of other factors--drugs people were taking, genetics, education, and class, to name a few--that could account for the increased risk, says Dr. Topol.
More importantly: Your blood type matters almost as little as a preseason NFL game. You never really need to know it--and the only thing it's truly important for is a blood transfusion (in which case you would be tested anyway to find out your type).
But here's when you should worry: if you're overweight and have a sedentary lifestyle, high blood pressure, or high cholesterol. Those factors, Dr. Topol says, have a whopping effect on heart disease. Not your blood type.
And while previous research has suggested that carrying type A or B blood may affect circulating levels of the "bad" LDL cholesterol and could be a risk factor for inflammation and heart disease, Dr. Topol says those connections are weak, too. "Linking a blood type with LDL cholesterol levels would be really important if it were established to be real--but that research is speculative, not accepted," he says.
In the meantime, forget your blood type and focus on what you can change: your lifestyle. Start smiling more, for starters. Optimists were 50 percent less likely to suffer a heart attack or stroke when compared to pessimists, according to a recent review of research in Psychological Bulletin. Here are 4 More Small Ways to Help Your Heart.