Nutrition: Bug off!

Can broccoli and green tea help fight those winter coughs and colds?

Yum… green tea and broccoli both contain quercetin, which seems to have immune-boosting properties

It’s well established that serious cyclists, and anyone else who undertakes intense, regular exercise, is at an increased risk of illness and infection.


The relationship is curved: people who do no exercise have a medium infection risk, which decreases as you build up to a moderate level of exercise. But if you go beyond moderate exercise, your infection risk goes up again – sharply.

Fortunately, the helpful folk at Appalachian State University in the US have uncovered a naturally occurring substance that may help. It’s called quercetin and though you may never have heard of it, you’ve probably been happily munching it for most of your life, albeit not in the quantities needed to stave off illness.

It belongs to a class of compounds called flavonoids and has strong anti-oxidant properties. It’s found in broccoli, green tea, red apples and red grapes. A normal diet will involve consumption of about 25-50mg of quercetin per day. Dr David Nieman and his research team gave trained cyclists 1000mg per day during an intense training period to see if it would reduce the infection risk.

Every day for five weeks, 20 cyclists were given the high dose of quercetin combined with vitamin C and niacin to help the body absorb the substance. A placebo was given to 20 other cyclists pursuing the same training regime. The study was double blind, meaning neither the cyclists nor the doctors involved knew who had been given what. 

Three weeks in, the researchers pushed the cyclists hard by having them do daily three-hour rides to exhaustion to weaken the immune system and increase the risk of picking up an infection. Nine of the 20 placebo cyclists promptly did, but only one of the athletes from the quercetin group fell sick following the extreme training.

If you’re planning on a few weeks of intense training, quercetin could be an incredibly effective tool for cutting your infection risk

“That’s a highly significant difference,” said Dr Nieman. “When you have a double-blind, placebo-controlled study and you have those kinds of differences, it can’t be due to chance.”

The researchers found that the immune-boosting properties of quercetin did not take effect until after the three-day intense exercise period.

They concluded that quercetin only acts when the going gets really tough, when stress hormones are incredibly high and the cyclist is suffering from high oxidative stress and muscle damage. 

So, if you’re planning on a few weeks of intense training, quercetin could be an incredibly effective tool for cutting your infection risk during that period, particularly as none of the subjects in the study reported any adverse side effects.

Nieman is doing a much larger study including non-elite athletes to see if quercetin may have benefits for the general public in coping with everyday stresses and strains. Part of this may come from a mental benefit which the scientists identified in the first study. 

They found that quercetin performed a similar function to caffeine, helping mental alertness and improving reaction time following the bout of intense exercise.

“The athletes taking the quercetin supplement maintained their ability to react to an alertness test when exhausted, whereas those who took the placebo became measurably slower,” said Dr Nieman.


Dr Nieman’s research was funded to the tune of $1.1 million by DARPA, the US Department of Defense’s high-risk R&D organisation. They hope the supplement will help maintain the immune systems of troops undergoing the extreme physical and mental stresses of combat. Good enough for a long cycle ride then!