Phytonutrients in citrus such as hesperidin may increase blood flow sufficient to warm the hands and feet of those with cold sensitivity.
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 you can measure blood flow through the skin using a laser beam, a laser Doppler fluximeter; sounds like something from Back to the Future. And if you give people the amount of hesperidin found in 2 cups of orange juice, blood flow goes up, though if you instead just give them the orange juice itself, that works even better, 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 in 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.
And these changes in blood flow are not just “in theory.” Researchers have taken volunteers with cold sensitivity, cold hands, cold feet, put them in an air-conditioned room and measured the temperature of their finger tips 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, but the fingers of those consuming low, or high doses of citrus didn't as much. That's because their blood flow remained steady—here's that laser test again. 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 as you can see their finger temperature rebounded faster towards normal in the citrus group. Having warm hands is nice, but maintaining blood flow to your fingers is not as important as maintaining blood flow to your brain.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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Because different families of fruits and vegetables can have entirely different phytonutrient profiles, variety is important. See, for example:
Eating oranges is always better than drinking juice. I'll discuss the difference more in the next video Reducing Muscle Fatigue with Citrus.
Please make sure to rinse your mouth with water after consuming sour fruits to protect your tooth enamel (see Plant-Based Diets: Dental Health).
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