In 1936, Albert Szent-Györgyi, who won the Nobel Prize for discovering vitamin C, described a vitamin “P,” which we now know encompasses a class of thousands of phytonutrients called flavonoids. Some, like quercitin, are widespread in plant-based foods. You can tell something is widespread in the plant kingdom when you can even find it in iceberg lettuce.
Others, however, are only found in specific plant families. For example, hesperidin is found primarily in citrus fruits. This may be one of the reasons that, out of all the different types of fruit that have been looked at, citrus may cut our risk of stroke the most.
The citrus phytonutrient hesperidin increases blood flow. Using a machine called a Doppler fluximeter (sounds like something from Back to the Future) you can measure blood flow through the skin using a laser beam. And if you give people the amount of hesperidin found in two cups of orange juice, blood flow goes up. It works even better if you give them the orange juice itself, so there’s other beneficial stuff besides just the hesperidin in citrus.
For example, if you measure the changes in genetic expression, orange juice consumption induces changes in the expression of 3000 of our genes, whereas hesperidin alone only modulated the expression of about 2000. Still, nearly 2000 stretches of our DNA expressed differently because we consumed just one of the thousands of phytonutrients in plants is pretty mind-blowing.
These changes in blood flow are not just in “theory.” Researchers took volunteers with cold sensitivity (cold hands and feet), put them in an air-conditioned room and measured the temperature of their fingertips after drinking a placebo drink (like orange Kool-Aid) versus drinks with two doses of actual citrus phytonutrients. In the Kool-Aid group their fingers got colder and colder, dropping nearly 9 degrees Fahrenheit. The fingers of those consuming low or high doses of citrus didn’t get nearly as cold because their blood flow remained steady. If you click on the above video, you can see the laser test of their blood flow. When you’re exposed to cold temperatures your body starts to clamp off peripheral blood flow to keep your core warm, but if you eat a bunch of oranges before you go skiing your risk of frostbite may go down since you’re keeping up your blood flow to your fingers and toes.
They even took these poor women and plunged their hands into some chilly water, and their finger temperature rebounded faster towards normal in the citrus group, demonstrating that citrus phytonutrients not only keep your extremities warmer but also warm you back up faster.
Just don’t brush your teeth immediately after consuming citrus. Make sure to rinse your mouth with water and wait 30 minutes before brushing to protect your tooth enamel (see Plant-Based Diets: Dental Health).
Because different families of fruits and vegetables can have entirely different phytonutrient profiles, variety is important. See, for example:
- Constructing a Cognitive Portfolio
- Garden Variety Anti-Inflammation
- Apples and Oranges: Dietary Diversity
- Fighting Inflammation with Food Synergy
Michael Greger, M.D.