How to Get Enough “Lifespan Essential” Polyphenols

Polyphenols are among the front runners in developing dietary approaches to fight age-associated disease. There is such a critical mass of data in favor of the protective benefits of these “lifespan essentials” that recommended daily intakes of polyphenols have been proposed. More than 8,000 different polyphenols have been identified, though only a small proportion have had their health effects cataloged. Shared structural features make them among the most powerful dietary antioxidants in vitro, but in our bodies, mechanistic effects have been attributed to their ability to modulate cellular signal transduction pathways.

In the PREDIMED trial, those in the top fifth of polyphenol intake had a 37 percent reduction in all-cause mortality compared to those in the lower fifth of consumption, which over an adult lifetime could translate into about four more years of life. However, the high polyphenol group was eating nine servings of fruits and vegetables a day compared to the five a day eaten by the low polyphenol group; so, it’s possible there were other phytonutrients at play. Coffee and tea are major sources, but in terms of foods, polyphenols come primarily from vegetables, fruits, then beans.

There are about a half dozen different types of polyphenols, including phenolic acids like the curcumin in turmeric or the lignans concentrated in flaxseeds, but the largest class are the flavonoids. Plant eaters may consume more than 4,000 different types of flavonoids on a daily basis. Flavonoids include the anthocyanin pigments in berries, the isoflavones in soy foods, the catechins in tea like EGCG, the flavonones in citrus, and the flavonols, like quercetin and fisetin, which people get from foods like apples, onions, and strawberries.

Like polyphenols generally, those who consume the most flavonoids tend to live significantly longer, according to a meta-analysis of 16 cohort studies following nearly a half million people for 5 to 28 years. However, those who get more are also more likely to be college-educated, non-Hispanic white with a higher income. The sharpest socioeconomic gradient was found for berry flavonoids. If you look at individual foods, though, as Harvard researchers did in the Nurses’ Health Study II, it wasn’t just blueberries and strawberries that were correlated with a lower risk of premature death, but also more affordable produce, such as apples and bell peppers.

To prove cause and effect, researchers randomized middle-aged men and women to eat higher- or lower-polyphenol diets in the Polyphenol Intervention Trial. Eight weeks later, the higher-polyphenol diet group enjoyed significant improvements in quality of life—both physically and mentally—compared to the lower-polyphenol diet group. But what did the two diets consist of? The lower-polyphenol diet group was told to restrict fruits and vegetables to no more than 2 servings a day, whereas the higher-polyphenol group was to eat six servings (including a portion of berries), plus two ounces (60 g) of dark chocolate a day. So, it could have been any number of fruit and vegetable components besides polyphenols responsible for the benefit. Just the enforced chocolate consumption might have boosted well-being! A more rigorous study design might be to randomize both groups to the same number of high-versus-low-polyphenol fruit and vegetable servings.

In the Nurses’ Health Study, you may have noticed that one food source of flavonoids was associated with an increased risk of all-cause mortality: grapefruit. Frequent grapefruit consumers were more likely to die prematurely than their non-grapefruit-eating compatriots matched for a large number of demographic and lifestyle factors. This was partly chalked up to grapefruit’s suppression of a set of detoxification enzymes in our intestines that may metabolize half the common drugs on the market. Broccoli has the opposite effect, boosting detox enzymes such that some drugs can be cleared faster, whereas even a single cup (240 ml) of grapefruit juice can reduce the rate of drug clearance for days, increasing the risk of potentially life-threatening drug side effects. That’s why grapefruit has been called a “pharmacologist’s nightmare.” If you’re on medications (including many common heart and blood pressure pills) make sure to talk to your prescriber about your grapefruit habits.