A team of ASU researchers found that nitrate-rich foods mitigated postmenopausal women’s risk for heart disease.
Spinach, romaine lettuce and celery are easily accessible, nitrate-rich foods.
Though much has been done over the past few decades to raise awareness about the threat of heart disease, it continues to be the leading killer of women in the United States, accounting for roughly 1 in 5 female deaths each year, with postmenopausal women at the highest risk.
Inspired by existing research that found dietary nitrate supplementation in the form of beetroot juice improved the vascular fitness of athletes, a team of ASU researchers set out to see what high-nitrate foods might do for postmenopausal women.
In their recently published study, College of Health Solutions doctoral student Selicia Mayra, College of Health Solutions professor Carol Johnston and School of Life Sciences associate professor Karen Sweazea found that postmenopausal women’s increased risk for heart disease was mitigated by eating high-nitrate, leafy greens.
The message was clear, Mayra said: “Eat more salads!”
Study participants were asked to consume a salad of either spinach, romaine lettuce or celery twice daily before their normal meals, for 10 consecutive days.
After a three-week washout period, they were asked to consume a low-nitrate, canned vegetable control of either beans, corn or peas before their normal meals, for 10 consecutive days.
Women’s nitrate concentration significantly increased following the salad treatment compared to the canned vegetable control, suggesting that daily ingestion of nitrate-rich, leafy green salads may prove a useful strategy for improving cardiovascular health in postmenopausal women.
ASU Now turned to Mayra and Johnston to find out what’s so great about leafy greens compared to beetroot juice and why, if you want the cardiovascular benefits of leafy greens, you should nix mouthwash altogether.
Question: Why do women have an increased risk for heart disease after menopause?
Johnston: When you look at the lifespan of an individual, men have a higher risk for heart disease early on, like in their 50s, than women.
But then it flips when women go through menopause.
Men have sort of a constant risk for heart disease. Women start with a lower risk and then it goes up once they hit menopause.
And what happens at menopause is estrogen falls. Estrogen is a trigger of nitric oxide, which is a basal dilator, meaning it widens blood vessels, which decreases blood pressure.
So women are sort of protected from heart disease for most of their lives because they have a natural way to trigger nitric oxide. But once they hit menopause, it decreases dramatically.
Q: How can eating leafy greens help?
Johnston: What’s interesting about nitric oxide is you can produce it endogenously, which means your body will make it, with estrogen triggering it.
But you can also provide your body with dietary nitrates that convert to nitric oxide, and leafy greens are full of nitrates.
Q: Your study notes that beetroot juice is also high in nitrates. Why didn’t you ask women to consume that instead of leafy greens?
Mayra: We wanted something that was sustainable.
We wanted foods that were not only high in nitrates but also antioxidants, as well as good sources of fiber; foods that are just good for you overall. So we really wanted to move away from the bottled, prepackaged foods to real foods that people can sustainably consume over time.
Johnston: Beetroot juice is typically sold as a concentrate, and it’s processed. It’s not like people are eating beets. So there’s a lot of processing and it’s expensive.
The beetroot juice craze is definitely a manufactured, novel supplement and companies are making pretty decent profits on it.
Mayra: And there’s so many brands of beetroot juice and sometimes it’s not regulated, so it tells you you’re getting this many nitrates in there but you don’t necessarily know for sure.
Q: Can everyone benefit from eating leafy greens?
Johnston: Of course. I think it’s important that people eat leafy salads all the time because they have fiber and phytochemicals and all these wonderful things.
They’re a good source of vitamin C, a good source of folate.
There’s a lot of antioxidants in lettuce. Epidemiological data suggest that people eat fruits and vegetables to lower their risk of cancer. But for postmenopausal women, eating leafy greens would be a strategy for avoiding high blood pressure.
Q: Is there a difference in nitrate levels between types of leafy greens?
Mayra: There is, but only slight differences. The three that we chose — spinach, romaine lettuce and celery — are some of the highest sources of nitrates.
Q: What are some other high-nitrate foods?
Johnston: Fresh beets are still at the top but we felt that these were the most easily accessible.
Mayra: Another leafy green that’s very high in nitrates is arugula.
Q: What is the major takeaway of this study?
Mayra: Eat more fresh, leafy salads.
Johnston: What’s interesting is that hypertension has a genetic component.
So if you have a history of hypertension or if you have a history of heart attacks in your family, you need to do something about it.
And it’s nice that if you start early, you might be able to delay having to go onto pharmaceutical meds.
You may need to go on meds eventually anyway; you don’t play around with hypertension.
But if you can keep your blood pressure under control by a simple strategy that doesn’t really disrupt what you eat, that’s great. We’re just saying start your meal with a salad.
Q: Was there anything people might find surprising about this study?
Mayra: Yes. We restricted mouthwash use for study participants because research has shown that antiseptic and antibacterial mouthwash sort of kill the bacteria in your mouth that’s required to turn nitrates into nitrites.
And nitrite is what we need because it turns into nitric oxide, which is what leads to the basal dilation.
So you can eat as much nitrates and salads as you want but it won’t get reduced to nitrite, and therefore, it won’t get reduced to nitric oxide if you’re using mouthwash.
DOI: 10.1016/j.nutres.2019.02.001.
