What does quercetin do in your body?
Quercetin has interesting properties in the lab and in small human studies, but whether supplements actually make a difference in practice remains unclear. Through ordinary foods such as onions and berries, you obtain the most bioavailable form without safety risks.
Quercetin is a plant compound found naturally in onions, berries, apples and broccoli. Eating 100 grams of berries per day can raise quercetin levels in the blood by around 50%. A diet rich in vegetables and fruit can nearly double that concentration, while a poor diet can lower it by 30%.
How much quercetin actually reaches the bloodstream after eating or taking a supplement varies enormously from person to person and from product to product: studies measure absorption rates ranging from 0 to more than 50%. The form matters a great deal. Quercetin from onions, where it is bound to glucose sugars, is absorbed most effectively. Standalone supplements are generally absorbed less well. Once absorbed, the body rapidly converts quercetin into breakdown products that circulate through the blood and are excreted in the urine. Interestingly, it appears to be precisely those breakdown products, formed by the liver and gut bacteria, that are responsible for much of the biological activity, sometimes even more so than quercetin itself.
In test-tube research (using isolated cells), quercetin shows strong antioxidant and anti-inflammatory properties. Whether this also holds true in the living human body is uncertain, partly because of that variable absorption. Population studies suggest that people with a higher quercetin intake have a slightly lower risk of cardiovascular disease, and a dose of 500 mg has, in some small studies, lowered blood pressure and certain inflammation markers. However, in other experimental studies in humans those effects did not appear, so a causal relationship has not yet been established. The same applies to cancer prevention: in the lab quercetin inhibits cell growth, but evidence from clinical studies in humans is lacking.
On safety: with short-term use of up to 1000 mg per day, side effects are rare and mild. Use lasting longer than twelve weeks at high doses has not been studied enough to draw conclusions. Animal research raises two points of concern: possible kidney damage in people who already have impaired kidney function, and possibly promoted tumour growth in oestrogen-sensitive cancers. Quercetin can also affect the absorption of certain medications, which is relevant if you are taking multiple drugs.
All claims are based on reviews (no randomised trials or meta-analyses). The mechanistic and animal data are promising, but robust clinical evidence in humans is largely lacking.
How healthy are yoghurt and dairy for your heart and bones?
Yoghurt and dairy are a perfectly good choice for bone health for most people, and are likely neutral to mildly beneficial for the heart. Opt preferably for fermented products such as yoghurt, and keep an eye on your total saturated fat intake if you have an elevated cardiac risk.
How much fibre do I need and why?
Aiming for 25 to 29 grams of fibre per day is well supported and delivers the greatest health benefit. Most people in Western countries fall well short of that, so eating more vegetables, legumes and wholegrain products is a smart step for almost everyone.
How much taurine do you need per day?
There is no established daily figure for taurine alone. Anyone who regularly eats fish, meat or dairy is probably getting enough. A supplement is unnecessary for healthy people and is not recommended.
How many fruits and vegetables do I actually need per day?
Five portions of fruit and vegetables per day (two pieces of fruit, three serving-spoon scoops of vegetables) is the number with the strongest evidence base; eating more does not provide additional benefit, but most people do not even reach this minimum.
Does eating fish help your heart and your brain?
Two portions of oily fish per week, as part of a varied and plant-rich diet, is a smart choice for most people when it comes to both heart and brain health. However, fish does not work as a standalone protective food.
Does eating a high-fibre diet help against constipation as you get older?
Eating more fibre helps with constipation in older adults, but the overall dietary pattern matters at least as much as fibre grams alone. Always drink enough water when taking fibre supplements, and consult your doctor if you use medications or are unable to drink sufficient fluids.