Phenylalanine comes in several forms as a supplement:
L-phenylalanine is an essential amino acid. It's also found in protein in the foods we eat.
DL-phenylalanine, which contains both the D- and L-forms
Early quercetin research on heart and vessel disease is mixed. Some study results are positive but some are open to debate. For example, researchers link eating lots of foods high in quercetin to a lower risk of heart-related death in older men. But other studies are less convincing.
Some research suggests that oral doses of quercetin may decrease pain from prostate infections.
Some athletes try to increase endurance and improve athletic performance by using quercetin. Although animal studies are promising, the effects in humans, if any, are likely small.
Some studies link a diet high in quercetin with a lowered risk of cancer. But more research is needed.
In general, much of the research on quercetin has been in animals or in cell cultures. More study is needed to prove quercetin's benefits and safety in humans, especially when taken as a supplement instead of in food.
Common oral dosages are 500 milligrams twice a day. People have also used lower dosages as well. However, optimal doses of quercetin have not been established for any condition. Quality and active ingredients in supplements may vary widely from maker to maker. This makes it hard to establish a standard dose.
Can you get quercetin naturally from foods?
Quercetin is abundant in nature and foods. People typically get between 5 and 40 milligrams a day from food. But if you eat lots of fruits and vegetables, you can get as much as 500 milligrams daily.
For example, think "quercetin" the next time you pour a glass of red wine, bite into a crunchy apple, treat yourself to some berries, flip a buckwheat pancake, slice an onion, or sip a cup of green tea. Other vegetables that have high amounts of quercetin include: